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thesis entitled

CRUSTAL THICKNESS OF NORTHEAST

RUSSIA
presented by

KEVIN G. MACKEY

has been accepted towards fulﬁllment
of the requirements for

M.S. GEOLOGICAL SCIENCES
degree in

 

 

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CRUSTAL THICKNESS OF NORTHEAST RUSSIA
By

Kevin George Mackey

A THESIS

Submitted to
Michigan State University
in partial fulﬁllment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Geological sciences

1996

ABSTRACT
CRUSTAL THICKNESS OF NORTHEAST RUSSIA
By

Kevin G. Mackey

The ﬁrst order crustal structure of the Magadan region and northeast Sakha
Republic (Y akutia), northeast Russia, is obtained by Simultaneously inverting for origin
times and travel time curves. As an average, a 37 km thick, 5992:0007 km/Sw crust
overlying an 7.961i0.015 km/sec mantle provides an excellent ﬁt to phase data listed in
the Maten'aly p0 Seismichnosti Sibiri bulletin. Travel-time curves for individual stations
are very close to this average, though there are some variations in both crustal thickness
and velocities; upper mantle velocities and crustal thickness appear to increase along the
southern edge of the OkhotSk-Chukotka volcanic belt and decrease in the upper Kolyma
River basin and along the trace of the proposed Moma Rift. Crustal thickness is greatest
at Khandyga, on the Siberian platform, and lowest at Yubileniya, which may lie within

the currently active Laptev Sea rift system.

ACKNOWLEDGEMENTS

First, I would like to thank Kaz Fujita for all the support and guidance over the
past two years, without which this project would not have seen completion. Secondly,
I would like to thank my parents for their love, support, and understanding during the past
several years. A million thanks to Trent Faust who slaved for weeks typing and checking
phase data used in this study (I’m glad I did not have to do all of it). Dr. Larry Ruff
deserves credit and thanks for the use of, and assistance with ’SQUINT’, his traveltime
inversion program. The University of Michigan Seismological Observatory provided the
computer resources for running ’SQUINT’. I thank Boris Koz’min and Dima Gunbin for
station infomtation and discussions of data processing methods used in the former Soviet
Union. I also thank the Yakut Science Center and World Data Center B for providing
seismological bulletins. Thanks to Boris Koz’min from Yakutsk, and Valentin Kovalev
from Magadan, who provided earthquake data and helpful comments on their respective
regions. Thanks to David Stone, Pavel Minyuk, Valentin Kovalev, the Gunbin family,
and the Koz’min family who made my stay in Russia educational, eventful, and fun.
Larun Izmailov was especially helpful in Magadan with Russian Customs, and in getting
me the nicest hotel room in the city (sorry Kaz). I thank Bill Cambray and Hugh Bennett
for Stimulating discussions and serving on my guidance committee. I also thank Tom
Vogel for discussion on some of my ideas. Diane Baclawski, the librarian has been most
helpful in ﬁnding sources for research. I thank Steve Riegel and all those before me for

building the foundation for this study. Many thanks to Diane and Cliff Gray, who

iii

 

 

provided transportation and a different perspective of Fairbanks. Thanks to Michelle, who
has done a great job of keeping me sane. This work is part of an ongoing cooperative
research program between the University of Alaska Fairbanks, Michigan State University,
the Yakut Institute of Geological Sciences, and the Magadan Experimental
Methodological Seismological Division to Study the tectonics and seismicity of northeast
Russia. This project was funded by the Incorporated Research Institutions for Seismology
Joint Seismic Program (IRIS-JSP), and by National Science Foundation (NSF) grants OPP
#92-24193 and OPP #94-24139. Additional funding and support for this project and
myself was provided by a Michigan State University teaching assistantship, the Michigan
State University College of Natural Sciences, the University of Alaska Geophysical

Institute, and the Scottish Rite Masons.

iv

TABLE OF CONTENTS

LIST OF TABLES

LIST OF FIGURES

INTRODUCTION

PREVIOUS STUDIES

METHODOLOGY AND REGIONAL CRUSTAL MODEL
INDIVIDUAL STATIONS

DISCUSSION

CONCLUSIONS

APPENDIX A

APPENDD( B

BIBLIOGRAPHY

vi

vii

14

41

79

85

87

95

98

LIST OF TABLES

Table 1. New origin times and time shifts from inversion for best
75 events 36
Table 2. Comparison of crustal thicknesses determined in this and other
studies 42
Table 3. Comparison of seismic velocities determined in this and Other

studies 43

vi

LIST OF TABLES

Table 1. New origin times and time shifts from inversion for best
75 events 36
Table 2. Comparison of crustal thicknesses determined in this and other
studies 42
Table 3. Comparison of seismic velocities determined in this and other

studies 43

vi

LIST OF FIGURES

Figure 1. Tectonic setting of northeast Russia and boundaries of
Study area
Figure 2. Seismic activity of northeast Russia

Figure 3. Moma rift system map
Figure 4. Laptev Sea rift system map
Figure 5. Magadan-Kolyma DSS proﬁle

Figure 6. Crustal structure map from study by Suvorov and

Komilova (1986)

11

15

17

19

Figure 7. Seismic stations and epicenters of earthquakes used in the
study

Figure 8. Change in relocated epicenters vs. year

Figure 9. Change in Pg phase relocated epicenters vs. azimuth

Figure 10. Change in Pn phase relocated epicenters vs. azimuth

Figure 11 Simpliﬁed fault map of the central and southern portions of the
study area.

Figure 12. Distribution of selected 75 events used in the study

Figure 13. Pg, and Pn data plotted using Materialy reported epicenters
Figure 14. Pg, and Pn data plotted using relocated epicenters

Figure 15. Sg, and Sn data plotted using Materialy reported epicenters
Figure 16. Sg, and Sn data plotted using relocated epicenters

Figure 17. Change in Pg phase relocated epicenters vs. azimuth for best
75 events

vii

LIST OF FIGURES

Figure 1. Tectonic setting of northeast Russia and boundaries of
study area
Figure 2. Seismic activity of northeast Russia

Figure 3. Moma rift system map
Figure 4. Laptev Sea rift system map
Figure 5. Magadan-Kolyma DSS proﬁle

Figure 6. Crustal Structure map from study by Suvorov and
Kornilova (1986)

Figure 7. Seismic stations and epicenters of earthquakes used in the
study

Figure 8. Change in relocated epicenters vs. year

Figure 9. Change in Pg phase relocated epicenters vs. azimuth

Figure 10. Change in Pn phase relocated epicenters vs. azimuth

Figure 11 Simpliﬁed fault map of the central and southern portions of the
study area.

Figure 12. Distribution of selected 75 events used in the study

Figure 13. Pg, and Pn data plotted using Materialy reported epicenters
Figure 14. Pg, and Pn data plotted using relocated epicenters

Figure 15. S g, and Sn data plotted using Materialy reported epicenters
Figure 16. Sg, and Sn data plotted using relocated epicenters

Figure 17. Change in Pg phase relocated epicenters vs. azimuth for best
75 events

vii

Figure 18.

Figure 19.
Figure 20.
Figure 21.
Figure 22.
Figure 23.
Figure 24.
Figure 25.
Figure 26.
Figure 27.
Figure 28.
Figure 29.
Figure 30.
Figure 31.
Figure 32.
Figure 33.
Figure 34.
Figure 35.
Figure 36.

Figure 37.

LIST OF FIGURES (continued)
Movement of relocated epicenters away from bulk of receiving
stations
Pg, and Pn data after initial inversion
PG, and Pn data inverted after removal of erroneous arrivals
Regional travel time curve
Station Magadan data
Station Takhtoyarnsk data
Station Stekolnyi data
Station Debin data
Station Myakit data
Station Omsukchan data
Station Seimchan data
Station Sinegor’e data
Station Talaya data
Station Kulu data
Station Susuman data
Station Nelkoba data
Station Ust’ Omchug data
Station Ust’ Nera data
Station Moma data

Station Sasyr data

viii

31

33

34

39

45

48

49

50

51

52

53

55

56

57

58

59

61

61

64

 

Figure 38.
Figure 39.
Figure 40.
Figure 41.
Figure 42.
Figure 43.
Figure 44.
Figure 45.
Figure 46.
Figure 47.
Figure 48.
Figure 49.
Figure 50.

Figure 51.

Figure 52.

LIST OF FIGURES (continued)

Station Zyryanka data
Station Tabalakh data
Station Batagai data
Station Saidy data

Station Naiba data

Station Yubileniya data
Station Tenkeli data
Station Yakutsk data
Station Khandyga data
Station Nezhdaninskoe data
Station Evensk data

Station Omolon data
Distribution of crustal thickness
Gravity anomaly map

Heat flow level map

ix

65

66

67

68

69

71

72

73

74

75

77

78

80

83

84

Introduction

In this study the ﬁrst order variations in crustal structure in northeast Russia are
investigated using seismic wave travel time data from regional seismic events published
in Russian seismic bulletins. Northeastem Russia is a region presently under compression
and uplift as a result of the convergence of the North American and Eurasian plates (e.g.,
Naimark, 1976; Cook et al., 1986; Riegel et al., 1993). This region is composed of a
series of exotic terranes which accreted in the Mesozoic (e.g., Parfenov, 1991) and then
participated in an apparently extensional episode in the Pliocene which resulted in the
formation of the Moma rift system (Grachev, 1973; Fujita et al., 1990a). This study is
conﬁned to the areas best covered by the Magadan and northern Yakut regional seismic
networks from the late 1970s to early 19905. This region lies approximately between 57-
70°N and 125-163°E and includes the Chersky seismic belt (CSB), the eastern portion of
the Siberian Platform, the Kolyma gold mining belt and the region around Magadan (Fig.
1; q.v., Koz’min, 1984; Parfenov et al., 1988; Fujita et al., 1990b). The study area is
centered approximately at the junction between the North American plate, the Eurasian
plate, and Okhotsk microplate or block. In the southern region, the Okhotsk microplate
is undergoing deformation as it is compressed and extruded as a result of the convergence
of the North American and Eurasian plates (Riegel et al., 1993; Riegel, 1994). The
deformation within the Okhotsk block results in a geographically large area of seismic
activity. Figure 2 shows the trends of microseismic activity within the study area.

Microseismicity within the CSB is heaviest in the vicinity of Susuman; but levels may

120 140 160 180

 

 

 

 

 

 

 

Figure 1. Plate conﬁguration of northeast Russia, showing boundaries between the
Eurasian (EU), North American (NA), Okhotsk (OK), Paciﬁc (PA), and Amur (AM)
plates. Solid lines denote established boundaries, while dashed represent diffuse or
inferred. Large arrows represent relative motions between plates, and small show relative
motion along individual boundaries. Stippled area covers the region considered in this
study. 1 = Yakutsk, 2 = Magadan, 3 = Kamchatka Peninsula, 4 = Chukotka 5 = Lena
River, 6 = Yana River. Adapted from Riegel (1994).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 2. All known locatable seismicity within the study area. Seismicity shown
ranges from approximately Mb = 2.0 to greater than 6.0. Seismicity is due to interaction
between the North American (NA), Eurasian (EU), and Okhotsk (OK) plates. Highly
seismic area represents the Cherskii Seismic Belt (CSB). 1 = Yakutsk, 2 = Magadan, 3
= Susuman, 4 = Zyryanka. Data from Materialy Po Seismichnosti Sibiri, years 1976-
1991, and Zemletryaseniya V SSSR, years 1962-1989. Additional data supplied by B.
Koz’min for Sakha Republic (Yakutia; personal communication, 1994), and L. Gunbina
for Magadan (personal communication, 1995).

4

be inﬂated due to mining. Since the mid 19605, when seismic networks were ﬁrst opened
in the area, approximately 5,000 CSB earthquakes have been catalogued and located.
North of the CSB, microseismicity declines rapidly. This may be partially due to station
distribution, but Riegel (1994) notes that the installation of a Station at Zyryanka (Fig. 2)
has not altered the microseismicity distribution.

The central portion of the study area is currently under transpression along the
North American and Eurasian plate boundaries. However, in the Pliocene this region
apparently underwent extension, forming the Moma rift system (Fig. 3). Within the past
0.5 m.y., the pole of rotation for the NA-EU plate is suggested to have moved north and
extensional activity along the Moma rift cease (Cook et al., 1986). The northern portion
of the study area includes the Laptev Sea rift system. The Laptev Sea rift system is the
extension of the Arctic Mid-Ocean Ridge onto the Siberian continental shelf, expressed
as a system of grabens (Fig. 4; Kim, 1986; Fujita et al., 1990a). Within the Laptev Sea
rift system, Kim (1986) suggests the Omoloi graben is the presently active zone of
extension. Drachev (1994) indicates extensional features throughout the southern portions
of the Laptev Sea. Microseismicity levels are highest along the southern edge of the
South Laptev basin (Fig. 4), although larger events are located both here and along the
Omoloi graben. Fewer microseismic locations in the Omoloi graben is likely a result of
seismic station distribution. The western portion of the Study area contains the eastern
portions of the Siberian platform. The Siberian platform generally consists of a ﬂat lying
Precambrian basement overlain by a few kilometers of Riphean, Cambrian, and Jurassic

sedimentary materials (Parfenov, 1991). Topographically, the Siberian platform is

 

 

     
  

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Figure 3. Map of the Moma rift system. Dashed lines Show faults bounding grabens
and half grabens, dotted where based on geophysical data. Cenozoic basins are Stippled.
AT denotes the Andrei Tas Range; UK the Uraga-Khaya dome and Dd the D’akhtardaakh
volcano. Other letter pairs label grabens: Ad=Adycha; Ch=Chondon; De=Derbeke;
Do=Dogdo (Darpir); EB=E1’ gen (Seimchan) - Buyunda; Ku=Khudzakh; Mo=Moma;
Ne=Nenneli; Om=Oimyakon; Or=Orotuk; Se=Selennyakh; Sy=Sellyakh Gulf; Ta=Talon;
Te=Tenkeli; Tg=Tagyn’ya; Tm=Tommot; To=Toustakh; Ts=Taskan; UN =Upper Nera;
Uy=Uyandina; Vy=Verkhoyansk (Upper Yana). Dots denote teleseismic earthquakes.
Triangles represent heat ﬂow measurements in mW/m’. Stars indicate volcanoes: white
for Late Cenozoic, black for Quaternary. From Fujita et al. (1990a).

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Figure 3. Map of the Moma rift system. Dashed lines Show faults bounding grabens
and half grabens, dotted where based on geophysical data. Cenozoic basins are Stippled.
AT denotes the Andrei Tas Range; UK the Uraga-Khaya dome and Dd the D’akhtardaakh
volcano. Other letter pairs label grabens: Ad=Adycha; Ch=Chondon; De=Derbeke;
Do=Dogdo (Darpir); EB=El’ gen (Seimchan) - Buyunda; Ku=Khudzakh; Mo=Moma;
Ne=Nenneli; Om=Oimyakon; Or=Orotuk; Se=Selennyakh; Sy=Sellyakh Gulf; Ta=Talon;
Te=Tenkeli; Tg=Tagyn’ya; Tm=Tommot; To=Toustakh; Ts=Taskan; UN=Upper Nera;
Uy=Uyandina; Vy=Verkhoyansk (Upper Yana). Dots denote teleseismic earthquakes.
Triangles represent heat ﬂow measurements in mW/m’. Stars indicate volcanoes: white
for Late Cenozoic, black for Quaternary. From Fujita et al. (1990a).

 

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Figure 4. Map of the Laptev Sea rift system. Dashed lines indicate faults, primarily
geophysically determined, and contours are for sediment thickness in km. Two letter
abbreviations denote Cenozoic grabens: Ke=Kengdei; Kh=Khopto; Ku=Keranak;
Se=Selennyakh; Te=Tenkeli; Uy=Uyandina; Yg=Yglan. Omb identiﬁes the Omoloi basin.
From Fujita et al. (1990a).

relatively flat.

Considering the regional tectonics, the crustal structure of the study area is
expected to be very complex. Due to its general inaccessibility, however, few seismic
studies have been conducted in northeast Russia; the few available studies are based on
isolated seismic refraction proﬁles, converted phases, and differential travel-times. None
of the long-distance refraction lines conducted throughout the Siberian platform reached
(Razinkova, 1987) this area. Thus, the crustal structure is poorly known and some of the
studies have resulted in contradictory results. The resolution of crustal thickness in this
area contributes to the understanding of the present-day tectonics of the area, the extent
of rifting during the development of the Pliocene Mama rift, and on the nature of the
North America-Eurasia plate boundary.

In addition to the resolution of crustal thickness in northeast Russia, this study was
also used to test the ’SQUINT’ traveltime inversion program with application to a wide
network. The ’SQUINT’ program was originally developed for use with a small local
network, and has never been applied to a large area with a regional network (Ruff et al.,
1994).

The Chersky seismic belt region was selected for study because of the relatively
dense network of seismic stations, which should result in better focal parameters, the great
nummr of earthquakes, and the presence of a 350 km long, deep-seismic sounding (DSS;
refraction) line conducted in 1959 between Magadan and Ust’ Srednikan on the Kolyma
River (Magadan-Kolyma DSS proﬁle; Davydova et al., 1968; Ansirnov et al., 1967). This

line can be used to calibrate crustal studies.

PREVIOUS STUDIES

Several previous studies have considered this region. The earliest study Of large
scale crustal structure in this region was the Magadan-Kolyma Deep Seismic Sounding
(DSS) proﬁle conducted in 1959. This proﬁle was conducted along the Magadan - Ust’
Srednikan highway for a total distance of 350 km between end shot points with
observations covering 156 km (Fig. 5). The proﬁle indicates a crustal thickness of 31 km
near Stekolnyi increasing to 38 km in the north (Davydova et al., 1968; Ansimov et al.,
1967). According to Ansimov et al. (1967), the proﬁle shows a 15 km thick granitic
layer with velocities ranging from 6.0 km/sec to 6.5 km/sec. Beneath the granitic layer
lies a 15-16 km thick basaltic layer where velocities are between 6.5 krn/sec and 7.0
kin/sec (Ansimov et al., 1967). The Moho, with a velocity of 8.1 km/sec underlies the
basaltic layer (Ansimov et al., 1967). Velocities shown on ﬁgure 5, also from Ansimov
et al. (1967) are not consistent with his text. Unfortunately, no direct data is available
beneath Magadan; however, by extrapolation with an offshore refraction line, a depth of
29-30 km is inferred (Fig. 5: Ansimov et al., 1967).

The most comprehensive crustal structure study in the area was by Suvorov and
Kornilova (1986). This Study used Russian bulletin data and travel time differences
between seismic Stations for common events to study crustal thickness and crustal and
mantle velocities. Their method initially assumes a homogeneous crustal strata and that
the refracted phase for individual events travels along a ﬂat underlying boundary

(Suvorov and Kornilova, 1985). Consistent changes in travel times for certain regions

PREVIOUS STUDIES

Several previous studies have considered this region. The earliest study Of large
scale crustal structure in this region was the Magadan-Kolyma Deep Seismic Sounding
(DSS) proﬁle conducted in 1959. This proﬁle was conducted along the Magadan - Ust’
Srednikan highway for a total distance of 350 km between end shot points with
observations covering 156 km (Fig. 5). The proﬁle indicates a crustal thickness of 31 km
near Stekolnyi increasing to 38 km in the north (Davydova et al., 1968; Ansimov et al.,
1967). According to Ansimov et al. (1967), the proﬁle shows a 15 km thick granitic
layer with velocities ranging from 6.0 km/sec to 6.5 km/sec. Beneath the granitic layer
lies a 15-16 km thick basaltic layer where velocities are between 6.5 kin/sec and 7.0
km/sec (Ansimov et al., 1967). The Moho, with a velocity of 8.1 kin/sec underlies the
basaltic layer (Ansimov et al., 1967). Velocities shown on ﬁgure 5, also from Ansimov
et al. (1967) are not consistent with his text. Unfortunately, no direct data is available
beneath Magadan; however, by extrapolation with an offshore refraction line, a depth of
29-30 km is inferred (Fig. 5: Ansimov et al., 1967).

The most comprehensive crustal structure study in the area was by Suvorov and
Kornilova (1986). This Study used Russian bulletin data and travel time differences
between seismic stations for common events to study crustal thickness and crustal and
mantle velocities. Their method initially assumes a homogeneous crustal Strata and that
the refracted phase for individual events travels along a ﬂat underlying boundary

(Suvorov and Kornilova, 1985). Consistent changes in travel times for certain regions

140 150 160

 

 
   

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Figure 5. The Magadan-Kolyma Deep Seismic Sounding (DSS) proﬁle and location
map. Left portion of ﬁgure shows a portion of a DSS proﬁle from the sea of Okhotsk.
Magadan is located at the 0 km point. 1 - sediments with velocities up to 2.5 km/sec; 2 -
sediments with velocities from 2.5 krn/sec to 6.0 km/sec; 3 - granitic layer with velocities
from 6.0 km/sec to 6.5 km/sec; basaltic layer with velocities from 6.5 krn/sec to 7.0
kin/sec; 5 - subcrustal layer with veldcities above 8.0 km/sec; 6 - deep boundaries
according to DSS data; 7 - deep boundaries in region of interpolation. From Ansimov

et a1. (1967).

dc

10

indicate variations in crustal thickness and seismic velocities. Their results suggest crustal
thicknesses increasing toward the east and west edges of this study area (24 km at Ust’
Nera to 38 km at Omsukchan in the east, and 44 km at Khandyga in the west), and upper
mantle velocities of 7.9 to 8.1 km/sec, with the higher values predominantly in the east
and west (Fig. 6). Their results are consistent with a signiﬁcant Pliocene rifting episode
resulting in an elevated and lower velocity upper mantle; this result is supported by the
surface wave polarization study of Lander (1984) which concludes that there is anomalous
mantle under the Chersky Range. Suvorov and Kornilova (1986) also conclude that
crustal (Pg) velocities are between 5.8 and 6.2 km/sec.

Crustal studies using P to P5 conversions were ﬁrst utilized for this area by Mishin
and Dareshkina (1966). For the study, the crustal velocity structure used was that
determined by the Magadan-Kolyma DSS proﬁle. For consistency, only earthquakes at
teleseismic distances were utilized (Mishin and Dareshkina, 1966). The original Mishin
and Dareshkina (1966) study calculated depths for only four of the stations used in this
study. It should be noted that only 6 earthquakes per station were used for the Mishin
and Dareshkina (1966) study. A later paper by Mishin et al. (1979) adds additional data
for stations Seimchan and Susuman. Their studies yield a generally thin crust in the
Kolyma gold belt, between 30 and 34 km, which increases in the north to 50 km at
Susuman. Belyaevsky (1974) attributes data identical to that of Mishin to Nikolaevsky.
Belyaevsky (1974) includes data beyond the Mishin and Dareshkina (1966) paper,
including a Moho depth of 43 km for Debin and 34 km for Garmanda (near Evensk; Fig.

5). A P-PS converted wave study by Belyaevsky and Borisov (1974) report generally

10

indicate variations in crustal thickness and seismic velocities. Their results suggest crustal
thicknesses increasing toward the east and west edges of this study area (24 km at Ust’
Nera to 38 km at Omsukchan in the east, and 44 km at Khandyga in the west), and upper
mantle velocities of 7.9 to 8.1 km/sec, with the higher values predominantly in the east
and west (Fig. 6). Their results are consistent with a signiﬁcant Pliocene rifting episode
resulting in an elevated and lower velocity upper mantle; this result is supported by the
surface wave polarization study of Lander (1984) which concludes that there is anomalous
mantle under the Chersky Range. Suvorov and Kornilova (1986) also conclude that
crustal (Pg) velocities are between 5.8 and 6.2 km/sec.

Crustal Studies using P to PS conversions were ﬁrst utilized for this area by Mishin
and Dareshkina (1966). For the study, the crustal velocity structure used was that
determined by the Magadan-Kolyma DSS proﬁle. For consistency, only earthquakes at
teleseismic distances were utilized (Mishin and Dareshkina, 1966). The original Mishin
and Dareshkina (1966) study calculated depths for only four of the stations used in this
study. It should be noted that only 6 earthquakes per station were used for the Mishin
and Dareshkina (1966) study. A later paper by Mishin et al. (1979) adds additional data
for stations Seimchan and Susuman. Their studies yield a generally thin crust in the
Kolyma gold belt, between 30 and 34 km, which increases in the north to 50 km at
Susuman. Belyaevsky (1974) attributes data identical to that of Mishin to Nikolaevsky.
Belyaevsky (1974) includes data beyond the Mishin and Dareshkina (1966) paper,
including a Moho depth of 43 km for Debin and 34 km for Garmanda (near Evensk; Fig.

5). A P-Ps converted wave study by Belyaevsky and Borisov (1974) report generally

 

11

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Figure 6. Results from Suvorov and Kornilova (1986) crustal structure study. Dots
represent seismic stations (1) and associated numbers are depths in kilometers (3).
Arrows indicate trends of Moho velocity, in km/sec (2). Numbers in brackets indicate
the number of events used in the determination of velocity (2). Contours show general

trend of crustal thickness (4). From Suvorov and Kornilova (1986).

 

 

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12
higher values of crustal thickness approaching 40 km. Vaschilov (1979) cites data from

Mishin and Dareshkina (1966), including a depth for Garmanda identical to that cited in
Belyaevsky (1974) (this station does not appear in Mishin and Dareshkina (1966)).
Vaschilov (1979) recalculates the crustal depths using a different formula. Crustal depths
generally increase about 2 km from the Mishin and Dareshkina (1966) values (Vaschilov,
1979).

The most recent study using P-Ps converted waves computes crustal thicknesses
at 43 permanent and temporary seismic stations throughout eastern Siberia (Bulin, 1989).
The velocity structure used in the Study was also from the Magadan - Kolyma DSS
proﬁle and other DSS proﬁles in adjacent areas. In addition, the regional near surface
geology was taken into account for individual Stations (Bulin, 1989). Values computed
by Bulin (1989) are consistently 1.5-3.0 km thinner than those computed by Mishin. This
is generally due to increasing the VW. ratio from 1.73 used by Mishin to greater than
or equal to 1.8 (Bulin, 1989), which seems a bit high. The justiﬁcation for this ratio
change is not clear. In direct contrast to Suvorov and Kornilova (1986), Bulin has
determined a thick crust reaching 40 km at Ust’ Nera, under the Chersky Range, and 40+
km in the Okhotsk-Chukotka volcanic belt (Bulin, 1989). Unfortunately, Bulin (1989)
does not list data for all the seismic stations used in his Study.

Sedov and Luchnina (1988) used mine blasts along a proﬁle between Tal-Yuryakh
and Susuman to detennine seismic velocities and layer thicknesses. The velocities
obtained are somewhat different from the other Studies cited above; a 5.5-5.6 km/sec

upper crust overlying a 6.5-7.3 km/sec lower crust and an apparent Moho refraCtion of

 

M

Ear
pro:

3110]

map
10 [h]-

and:

13
10.6 km/sec. The high Moho velocity is attributed by them to a thinning of the crust in

the direction of the proﬁle; this end of the proﬁle was not reversed. In a continuation of
this study, Sedov (1993) conducted DSS proﬁling along the central Kolyma Highway
including the Susuman - Maisky - Myaudzha and Susuman - Neksikan - Kadykchan
branches. This DSS proﬁle indicates a crustal thickness of 41.5 km at Susuman,
decreasing to 37.1 km at Yagodnoe in the east and increasing to 43 km in the northwest
at Tal-Yuryakh (Sedov, 1993; Fig. 5).

In the northern portion of the Study area, Avetisov and Guseva (1991) used the
Method of Reﬂected Wave Sounding (MRWS) to construct seismic proﬁles of the Earth’s
crust in the Omoloi graben. A crustal thickness of 29 - 31 km was established for the
southem portion of the graben, in the vicinity of station Naiba (Avetisov and Guseva,
1991). This thickness is supported by a DSS proﬁle in the southern Laptev sea (Kogan
1974) and a compilation of previous work (Avetisov, 1983) which indicate a crustal
thickness of 29 - 30 km overlying a mantle with a velocity of 7.5 km/sec.

Neustroev and Parfenov (1985) have found a correlation between thickness of the
Earth’s crust and thickness of platform cover deposits from deep seismic sounding
proﬁles. From this correlation, correction factors were introduced into the Bouger
anomalies to remove the effect of the platform cover. Using several DSS proﬁles,
gravimetric maps, and a l:2,500,000 map of topography of the crystalline basement, a
map of crustal thickness was produced for the eastern Siberian platform. Of relevance
to this study, the crustal thickness was determined to be 42 km at Yakutsk and Khandyga,

and 40 km at Nezhdaninskoe (Neustroev and Parfenov, 1985). Neustroev and Parfenov

14

(1985) indicate anomalies due to thick platform cover are sufﬁcient to mask any anomaly
resulting from variations in crustal thickness. This calls into question previous methods
which have determined crustal thicknesses in the Siberian platform using gravity.
Intracrustal structure, based on gravity variations, has been extensively studied
using the method of Vashchilov (1984) for the entire region. Bobrobnikov and Izmailov
(1989) use gravity data to suggest 30-35 km crustal thicknesses for the study area,
increasing to as high as 60 km southwest of the study area. Deep seismic sounding is
reported to have obtained a crustal thickness of 38 km in the upper Yama River valley

(Bobrobnikov and Izmailov, 1989; Fig. 5).

Methodology and Regional Crustal Model

For this study, a data base of travel time data from over 850 regional events
occurring in the Magadan region, Sakha Republic (Y akutia), and the Laptev Sea was
created. Data from 1976 to 1990 are taken from Materialy po Seismichnosti Sibiri and
covers both the Magadan region and Sakha Republic (Yakutia). From 1991 to 1994,
additional unpublished data was provided by B. M. Koz’min for the Yakut network
(Personal communication, 1994) and by L. Gunbina for the Magadan network (Personal
communication, 1995). These data were supplemented by phase data for approximately
50 events reported in the International Seismological Center Bulletin and the Obninsk
Seismological Bulletin for stations in northeast Russia. The study area was selected based

on the distribution of the regional seismicity and the location of seismic stations. Figure

15

130 140 150 160

 

70

 

CES

MO

M

 

  

.YAK > A

2]

v

x:

60

 

 

 

 

 

 

\
N

 

Figure 7. Study area Showing seismic stations and epicenters of earthquakes used in
the study. MAG = Magadan, TTY = Takhtoyamsk, MGD = Stekolnyi, EVE = Evensk,
OMS = Omsukchan, TL- : Talaya, MYA = Myakit, USO = Ust’ Omchug, NKB =
Nelkoba, SNE = Sinegor’e, DBI = Debin, SEY = Seimchan, OMO = Omolon, KU- =
Kulu, Suu = Susuman, CGD = Chagda, YAK = Yakutsk, NZD = Nezhdaninskoe, KHG
= Khandyga, AYK = Artyk, UNR = Ust’ Nera, SSY = Sasyr’, ZYR = Zyryanka, MKU
= Mama (Khonou), CES = Cherskii, TBK = Tabalakh, BTG = Batagai, SAY = Saidy,
TLI = Tenkeli, YUB = Yubileniya, KYU = Kyusyur, NAY = Naiba, TIK = Tiksi, SOT
= Stolb.

7 sh
even

thee

1&ch
Etcr
proc:

asal

Russia

ch~ .
«ills:

I6

7 shows the boundaries of the study area as well as seismic stations and epicenters of
events considered in the study. In total, 441 events from the original data set fall within
the study area.

All events were relocated using Pg arrivals only, assuming a 6.00 km/sec crustal
layer, as well as ﬁrst arrivals (Pg or Pn) using Jeffreys-Bullen travel-times (Appendix A).
Events with fewer than four arrivals were not possible to locate. In the relocation
process, many misidentiﬁed phase arrivals were discovered. A Pn arrival misidentiﬁed
as a Pg anival Stands out in a Pg location with a large negative residual. Likewise, a Pg
arrival misidentiﬁed as a Pn arrival Shows clearly in a Pn location with a large positive
residual. In such cases, the phase of the arrival was corrected, and the event relocated.
For events with large residual arrivals which did not correspond to any possible
misidentiﬁed phases, the anomalous arrival was removed from the relocation process.
During the 19805, most of the stations‘in this region used the "Mayak" timing system with
an accuracy of about 0.3 sec; combined with reading uncertainties, errors of 0.4-0.5 sec
are expected; no attempt was made to reduce statistical residuals below this level. The
most recent determinations of station coordinates and their elevations were used in the
relocations. For Yakutian stations, new coordinates and elevations were determined from
1:200,000 topographic maps with assistance from B. M. Koz’min (Appendix B; Personal
communication, 1994).

In the relocations. most epicenters moved only 1-20 km relative to those given in
Russian bulletins. For events in which ﬁve or more arrivals were used in the relocation,

change in epicenter vs. year was plotted (Fig. 8). There is no evidence that the Russian

17

 

 

 

 

 

I50 I T I I I l I I T I
140 — —
130 — —
120 - -
110 - ° —
O .
100 P o -
o
90 — ° —
o
80 — 4
7o 1— o 0 -
0 O
60 -— o _
o
50 - —
0
4O - O O o —
o O 0 O
30 ~ 0 0 o o —
o
O 0 g 8 8 o o 8 8 O o
20 _. 8 o 8 o 8 g o 8 ..
Q a 0 O 8 O O
10- go iggggiggsogg e
O (P 9 8 E g (P T a g I O r
76 78 80 82 84 86 88 90 92 94
Figure 8. Year vs. change in' kilometers of relocated epicenters for events shown in

Fig. 7. Relocations computed with Pg phase only, assuming a single layer crust of
velocity 6.00 km/sec. Lack of systematic trend through time indicates that the quality of
original locations has remained consistant. Original epicenters taken from Materialy Po
Seismichnosti Sibiri.

dc;
dc;
cor
det

rtlt

BIC}
011

tho:
[0 b
Sex-t
For
T610,

dete.

18

epicenters improve in later. years, even with better station distribution and presumably
more accurate timing. There is evidence for systematic mislocations in the Russian data
set. Relocations computed with Pg arrivals Show a strong tendency to move south, and
to a lesser extent north, relative to the Materialy reported epicenter (Fig. 9). This is
likely due to a difference in the crustal velocity used in the different locations, and is
discussed below. Relocations using ﬁrst arrivals show no systematic trend (Fig. 10).
Many events reported in the Russian bulletins report a calculated depth. In most cases,
I was unable to calculate depths in the relocation process. For events where a shallow
depth was determined, there is no consistent correlation with the Russian bulletin reported
depths. Thus, for this study, most depths were conﬁned to 10 or 15 km. Relocations
computed early in the study used a conﬁning depth of 15 km, while more recent
determinations use 10 km In general, this change seems to have little effect in the
relocation process.

The Pg relocated epicenters were plotted on a simpliﬁed fault map of the Study
area (Fig. 11). Fault locations are from Irnaev et al. (1994), as well as lineaments visible
on landsat images. Activity on many of these faults is restricted to smaller events than
those locatable with phase data in Materialy po Seismichnosti Sibiri, thus faults known
to be active may not Show activity on this map. Relocated epicenters correspond well to
several of the mapped faults, such as the left-lateral Ulakhan fault (Irnaev et al., 1994).
For events believed associated with the Ulakhan fault, the bulletin epicenters and
relocated epicenters were plotted on 1:500,000 scale topographic maps in an attempt to

detennine whether or not the relocated epicenters Show an improved correlation with the

an
Lu '-

 

(ZD v ,
O [_——T

 

4O 1

19

 

30-

 

20-

 

10—

 

 

I l l

 

 

 

 

 

 

I I l

 

l J

 

120 1

60 90

120 150

180 210 240 270 300 330 360

 

110 -°
100 -
90 -
80 —
7o - 0
so -
50 —
40
so —
20-

10%?)

0|

 

30 60 90

Figure 9.

ooo°°

0.9 0.58.. °

Azimuth from original to Pg data relocated epicenter vs distance of
epicenter change (in km). As shown in the upper portion of the ﬁgure, epicenters tend
to move south, indicating a systematic error in the original locations. Original epicenters

‘2) 00:0

5:89:98}?

taken from Materialy Po Seismichnosti Sibiri.

Oooo

Maia

120 150 180 210 240 270 300 330 360

C

‘

 

 

20

 

 

 

 

150 r I I T I I I I I I I o

140 e —

130 - _.

1 - i

20 D 0

110 F -

100 F i _ CI“

90 _ D D -

80 - —

:1

7O - 4

60 —- D -l

50 — D 0 u -

40 _. at: D D _
D D D

30 — D u a D a-

n I: D o D

20 -° 0 0 a c, m 0a on o o ..
n 0 ° 0 d” 0 ”CI?

lO-E'Do on 00d?) 00!? 00000-4
0 DO U D D B D U @U (ml

ODBID 1013401ch I) 10 P 1001 OLD
0 3O 60 90 120 150 180 210 240 270 300 330 360

Figure 10. Azimuth from original to Pn data relocated epicenter vs distance of
epicenter change (in km). Epicenters Show no systematic direction of change. Original
epicenters taken from Materialy Po Seismichnosti Sibiri.

150 I

20

 

140 -
130 e
120 -
110 —
100 L-
90 _
80 _
70 e
60 —
50 —
40 r 0°

0
30 - '3
20 — D
10

EDD
810

 

I—
U
0

0° cr

0 o

D 0 C1
C1 0 D
D U m D
D D D
at“? @D D
cr :1
DD 0
P r 1 10

u
a 0°
0 ED
rUQI Q 1

 

[DU 1 U

 

0

O 30 60 90

Figure 10.

£521
0
O

120 150 180 21 240 270 300 330 360

Azimuth from original to Pn data relocated epicenter vs distance of

epicenter change (in km). Epicenters show no systematic direction of change. Original
epicenters taken from Materialy Po Seismichnosti Sibiri.

20

150 I I I I I I I I I I I

 

MO— 5
130- 4
mo- 0 —
no» —
mo- ' g o—
90— 0 D —
80- -
7o- 4
60— D a
50L 1:: U-

40- on —

I
0
0

Q3

:1
1

30

D U 0
20+- 0 D g D m an 0

D
o

10
O

 

 

1:: u U D n D g
D 1

1:1
1:1
B 1001010? Cl

1
O 30 60 90 120 150 180 21

on a
P 1 1 10

 

Figure 10. Azimuth from original to Pn data relocated epicenter vs distance of
epicenter change (in km). Epicenters show no systematic direction of change. Original
epicenters taken from Materialy Po Seismichnosti Sibiri.

155

 

 

 

 

 

 

 

 

 

 

 

 

(,
'\/ j
k
\

 

 

 

 

 

 

 

k‘? *8 °
IAN . J/VK %
‘3‘

1 ‘ ‘ f
i 2:1

 

 

 

 

.1
. \
z \
‘\
..\.
is,
T11: ‘x
X
8

 

 

 

 

 

 

‘3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

/ Sea

 

Figure 11. Map of major faults in the southern portion of the study area and their
relations to relocated epicenters. Solid lines represent faults mapped in Imaev (1994), as
well as those visible as lineaments on satellite images. Dashed lines represent faults
inferred from linear trends in relocated epicenters. UL denotes the Ulakhan fault; A-T
the Arga-Tas; D the Darpir; I-D the In’yali-Debin; E the Elgin; O the Oimyakon; E0 the
Eastern Okhotsk; C-Y the Chia-Yureya; C-M the Chelomdzha-Yama; K the Ketanda;
Ad-T the Adycha-Taryn.

21

155

 

 

 

 

 

65

 

 

 

 

 

 

 

(I
,\/ .
42%

'\

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 11. Map of major faults in the southern portion of the study area and their
relations to relocated epicenters. Solid lines represent faults mapped in Imaev (1994), as
well as those visible as lineaments on satellite images. Dashed lines represent faults
inferred from linear trends in relocated epicenters. UL denotes the Ulakhan fault; A-T
the Arga-Tas; D the Darpir; I-D the In’yali-Debin; E the Elgin; O the Oimyakon; E0 the
Eastern Okhotsk; C-Y the Chia-Yureya; C-M the Chelomdzha-Yama; K the Ketanda;
Ad-T the Adycha-Taryn.

22

fault trace. There is no apparent improvement in the correlation between relocated
epicenters and the Ulakhan fault trace relative to the Russian detennined epicenters. This
may be a result of the lack of knowledge regarding the structure of the Ulakhan fault at
depth, and poor depth control for both the relocated and bulletin reported epicenters.
Some of the events plotted may actually occur on unrecognized faults in the vicinity of
the Ulakhan. For many of the events, the Ulakhan fault trace is within the location errors
as discussed below.

The best located 75 events were selected for the determination of crustal Structure.
Several criteria were established for selecting these events (Fig. 12). First, events were
required to contain seven or more arrivals used in the Pg relocation. Fewer arrivals than
seven causes individual stations to be weighted heavily, thus one mispicked arrival could
result in considerable error in the relocation. Secondly, the azimuthal coverage had to
exceed 130°. For events where the range of azimuths was less than 130°, the event could
Simply be moved towards or away from the recording stations, trading off only with
origin time, and having little effect on the residuals. Lastly, the difference in epicenters
between the Pg relocation and the ﬁrst arrival relocation should not exceed 15 km, and
the difference in origin times should be less than 2.0 sec. These criteria were intended
to select events where the ﬁrst arrival times were compatible with the Pg relocated
epicenter, thus increasing the likelihood of good data. Because of the poor distribution
of recording Stations, the ﬁrst two criteria were difﬁcult to meet for events near the edge
of the study area, or away from the network. This was particularly true for events in the

Laptev Sea. In an effort to use a widely distributed data base, these criteria were

23

130 140 150 160

 

 

70

ha

CES

MO

‘3: M

 

60

 

 

 

 

 

 

 

\
N

 

Figure 12. Relocated epicenters of the selected best 75 events in the study area. These
events used in the determination of crustal thicknesses. Seismic station codes as noted
in Fig. 7.

24

somewhat lesSened for outlying events.

For the best 75 events, relocated epicenter errors range from :1 to 1'8 km,
averaging 21:3 km. It was noted that for events occuning from 1991 to 1993, average
errors for the relocations increased slightly to 21:4 km. The calculated errors on the
relocated epicenters are less than the location errors reported in the Materialy bulletin.
Bulletin reported epicentral errors average about :10 km for these 75 events.

To assess the precision of the epicenters reported in Materialy and compare them
with the Pg relocations, the travel-time data for the 75 selected events was plotted.
Looking at the Pg data, there is a signiﬁcant reduction in scatter of the arrival times using
the Pg relocation epicenter and origin time compared to those reported in Materialy (Figs.
13 and 14). This suggests problems with the reported epicenters.

A signiﬁcant reduction in scatter of the Pn data is also observed when plotted with
the Pg relocation parameters and compared with the plot using the Materialy parameters
(Figs. 13 and 14). Sg and Sn data are also plotted using Pg location parameters, though
they show a lesser reduction in scatter when compared to the data plotted with the
Materialy epicenter and origin time (Figs. 15 and 16). For all phases, the use of the Pg
phase relocated epicenter and origin time in place of those from Materialy results in a
reduction of scatter in the plotted travel time curves. Therefore, my relocations using
only Pg data are most certainly an improvement on the Russian locations.

Comparing the Pg travel time curves, it is apparent that the Russian locations are
determined with a higher Pg velocity. A velocity of 6.10 km/sec ﬁts the Pg travel time

curve derived from the original Russian locations (Fig. 13). This is consistent with the

$01116

Looki
the Pg

13 an:

the Pg
(Figs.
they 5
Maren
Phase :
Itducrj

Only P1

24

somewhat lessened for outlying events.

For the best 75 events, relocated epicenter errors range from :1 to :8 km,
averaging :13 km It was noted that for events occuning from 1991 to 1993, average
errors for the relocations increased slightly to :4 km. The calculated errors on the
relocated epicenters are less than the location errors reported in the Materialy bulletin.
Bulletin reported epicentral errors average about :10 km for these 75 events.

To assess the precision of the epicenters reported in Materialy and compare them
with the Pg relocations, the travel-time data for the 75 selected events was plotted.
Looking at the Pg data, there is a signiﬁcant reduction in scatter of the arrival times using
the Pg relocation epicenter and origin time compared to those reported in Materialy (Figs.
13 and 14). This suggests problems with the reported epicenters.

A signiﬁcant reduction in scatter of the Pn data is also observed when plotted with
the Pg relocation parameters and compared with the plot using the Materialy parameters
(Figs. 13 and 14). Sg and Sn data are also plotted using Pg location parameters, though
they Show a lesser reduction in scatter when compared to the data plotted with the
Materialy epicenter and origin time (Figs. 15 and 16). For all phases, the use of the Pg
phase relocated epicenter and origin time in place of those from Materialy results in a
reduction of scatter in the plotted travel time curves. Therefore, my relocations using
only Pg data are most certainly an improvement on the Russian locations.

Comparing the Pg travel time curves, it is apparent that the Russian locations are
determined with a higher Pg velocity. A velocity of 6.10 km/sec ﬁts the Pg travel time

curve derived from the original Russian locations (Fig. 13). This is consistent with the

25

 

 

 

 

 

 

 

 

 

 

 

 

 

20
Vr= 6.00 km/s
A X
3 .9
I": Y 0 Y
0
x A
+ +
+ + +
—20 + o
0. X (km) 1000.0
20
3
,:
Y
-20
O. X (km) 1000.0
Figure 13.

Reduced traveltime curves for Pg (A) and Pn (B) data of selected best 75
events using epicenters and origin times reported in Materialy po Seismichnosti Sibiri.

Reduction velocities are noted on ﬁgures. For Pg data, the best ﬁt velocity is 6.10 km/sec
(optically determined). Individual events are represented by different symbols.

(S)

Ir

RA.

-5 ‘h
Lv

(

(S)

Tr

Figure
events
Rcduct
IOijC‘1

20

Tr (S)

—20

20

25

 

 

 

Vr= 6.00 km/s

 

 

 

1000.0

 

Vr= 8.00 km/s

 

Tr (s)

 

-20

 

 

 

Figure 13.

X (km)

1000.0

Reduced traveltime curves for Pg (A) and Pn (B) data of selected best 75

events using epicenters and origin times reported in Materialy po Seismichnosti Sibiri.
Reduction velocities are noted on ﬁgures. For Pg data, the best ﬁt velocity is 6.10 km/sec
(optically determined). Individual events are represented by different symbols.

20

 

Vr= 6.00 km/s

 

 

 

 

 

 

 

 

 

 

 

 

fa? -. Y
V o
I:
x
+ o
-20
O. X (km) 1000.0
20
x Vr=» 8.00 km/S
A o
’0? O
I: +
-20 Y
O. X (km) 1000.0

Figure 14. Reduced traveltime curves for Pg (A) and Pn (B) data of selected best 75
events using epicenters and origin times determined from relocations using Pg data.

Reduction velocities are noted on ﬁgures. Individual events are represented by different
symbols.

26

 

20

Ir (3)

 

 

Vr= 6.00 km/s

 

 

 

—20

x (km) 1000.0

 

20

 

x Vr= 8.00 km/s
o

 

Ir (5)

 

 

 

-20

Figure 14.

x (km) 1000.0

Reduced traveltime curves for Pg (A) and Pn (B) data of selected best 75

events using epicenters and origin times determined from relocations using Pg data.
Reduction velocities are noted on ﬁgures. Individual events are represented by different

symbols.

27

 

 

 

 

 

 

 

 

 

 

 

20
o Vr= 3.50 km/s
x
x
E °.
i a 0
Y Y,
to OY
o
-20
O. X (km) 1000.0
20 + o
O X
+4 Vr= 4.500km/s
x is; Y x
fi-e O i Y T 0 A + + o
0.. .gigs,. .0
GAY} 0* 003(0vo 0 x 0 xx
1; x x A o "
v Y 0" x Abg‘
,:
o
-20
O. X (km) 1000.0

Figure 15. Reduced traveltime curves for Sg (A) and Sn (B) data of selected best 75
events using epicenters and origin times reported in Materialy po Seismichnosti Sibiri.

Reduction velocities are noted on ﬁgures. Individual events are represented by different
symbols.

27

20

 

0 Vr= 3.50 km/s

 

Tr (s)

 

 

 

 

 

 

 

 

 

-20
O. X (km) 1000.0
20 o x + o
% +5 Vr= 4.500km/s
x
set-f O E Y 9 o x A + + o
o b 5 6+ 99x6 0 " 0 Y o
o A Y o 00* o o ‘o o x x x
I x Ym. x 0 x3 40 2 A
A x x O X
\U')’ Y O“ X 45%
I:
o
-20
0. X (km) 1000.0
Figure 15.

Reduced traveltime curves for S g (A) and Sn (B) data of selected best 75
events using epicenters and origin times reported in Materialy po Seismichnosti Sibiri.

Reduction velocities are noted on ﬁgures. Individual events are represented by different
symbols.

28

 

 

 

 

 

 

 

 

 

 

20
o Vr= 3.50 km/s
X
A X Y 4,
A
’ 0‘ X o Y XX“ 0 0 .,_.”,:a R 0 Y”)! O X
A AY ‘ﬁ‘a‘. ., .:° .‘I‘.".'§.r‘;.‘€£‘.-. 1r, ;i'¢ ,.'. £ a f M gag + x
U) . £2." ‘ "- "(JET-'5: "y" :.-'-:L:70 0.431? ° ° A y ‘H ’<
'5. 0“ g," Y
; 6) 4* X T 00. X0. & X0 0 X 8+ 9
0+ 9 9 O Y 0
*r 9 b 4‘ Y o
X
—20 e
o. x (km) 1000.0
20 r x
°x 0 o 9 Vr= 4.50°km/s
X
4X +x Y ’ +
A o + 0 Y + o
x $14: 802:0 if 0* o 0 °
00 9901!? wgqi9§ogmgo oxoo A x
Y 013 A0 A0 9 ’It X x
O
A
1;; 0"
V 0
g Y
I—
O
X
-20
o. x (km) 1000.0
Figure 16.

Reduced travel time curves for Sg (A) and Sn (B) data of selected best 75

events using epicenters and origin times determined from relocations using Pg data.
Reduction velocities are noted on ﬁgures. Individual events are represented by different

symbols. Note reduced scatter in data when compared Fig. 15.

29

travel time curve used in Magadan, which assumes a 6.1 km/sec crustal layer, according
to D. Gunbin (Personal communication, 1995), and Andreev, (1984). The different Pg
velocities used can account for the systematic change in epicenters that are apparent in
the relocations (Fig. 9). The tendency for epicenters to move south is also evident when
looking only at the selected events, although to a lesser degree (Fig. 17). In locating
earthquakes, if one uses too high a velocity for Pg, but a correct velocity for Sg, the Pg-
Sg time interval will be increased for any given distance. Thus, when using such a travel
time curve, the apparent distance between epicenter and station will be decreased, and the
origin time will be late. Note on ﬁgures 15 and 16 that a velocity of 3.50 km/sec ﬁts the
S g data equally well using the bulletin or relocated epicenters. If the station distribution
around the epicenter is not symmetric about 360° (which is the case for virtually all
events in the study area), the epicenter will move toward the majority of the recording
stations. Using a slower Pg velocity, the Pg-Sg time intervals will decrease for a given
distance. In this case, the epicenter will move away from the recording stations, and
origin time will be earlier. This occurs with the Pg arrival relocated epicenters. Figure
18 shows the azimuth from epicenter to station, relative to azimuthal change in epicenter
for the relocation, using 26 events randomly selected from the best 75. For these events,
there are a total of 230 Pg arrivals. I found that the epicenters moved away from the
recording station in 142 of the arrivals (61.7%) and moved towards the recording station
in 88 arrivals (38.3%). For the best 75 events, the origin times shifted an average of 1.16
sec earlier. In total, 56 events shifted to an earlier time, 19 shifted later, and one

remained constant. With the above evidence, and considering the reduction of scatter of

30

 

100 I I I I I I I I I I I

90*- —
80~— -—
70— —
60— —
50— -
40—. —
30— o o —
20- o ..

o
00 g (p (b O O @ 0% O“
O o 0 000 oo
00 o CDC 0 Goo oo 0
(pl OJ 100 I él) Iy Io rh %1 l l

O 30 60 90 120 150 180 210 240 270 300 330 360

CIU

10

 

 

0

 

Figure 17. .For selected best 75 events, azimuth from original to Pg data relocated
epicenter vs. distance of epicenter change (in km). Epicenters tend to move south,
indicating a systematic error in the original locations. Original epicenters taken from
Materialy Po Seismichnosti Sibiri.

31

 

I T I I
(II) 0
00 CID O
00 00000
(XI)
0 (I)
O
000 Oq
000 O
O
000
0 0C
0
O 00
000 O
O O
OOCDO
O O
000:1.
J 1 1 n

 

 

 

 

-180—150—120-90-60 -30 O 30 60 90 120150180

Figure 18. Angle between azimuth from relocated epicenter to station and azimuth
from original epicenter to relocated epicenter for 26 of the selected best 75 events. This
ﬁgure illustrates that the relocated epicenters tend to move away from the bulk of the
receiving stations. Relocation moved the epicenter away from the recording stations in
142 out of 230 arrivals, denoted by the shaded regions of the plot.

32
data for all phases when plotted with the Pg relocations, I conclude that the 6.1 km/sec

Pg velocity used to determine locations listed in the Materialy catalog is too high.
Research by D. Gunbin (Personal communication, 1995) also indicates improved locations
when a slower crustal velocity of 6.0 km/sec is used for the Magadan region.

The method of earthquake location used for most of the epicenters reported in
Materialy may also contribute to errors in the epicenters. Earthquakes in the Sakha
Republic (Yakutia) are still located by drawing arcs on large scale (approximately
1:8,000,000) paper maps. Considering the scale of the maps and thickness of the pencil
line being drawn, errors of several kilometers may be introduced into the location process.
These errors would probably be random with respect to azimuth.

In order to determine the ﬁrst-order crustal structure, the method of Ruff et al.,
(1994) ’SQUINT’ is used. This method assumes that regional travel time curves for
multiple earthquakes can be approximated with a regional average crustal model. Given
a set of earthquakes, the Pg travel time data are simultaneously inverted, solving for the
best ﬁt velocity for the set of events, and new origin times for individual events,
assuming ﬁxed hypocenters. For a given station, any systematic variation from the
regional average should be a result of local variations in crustal structure. The Pg data
was initially inverted with all spurious arrivals included (Fig. 19). Although this results
in an increase in data scatter compared with the non-inverted data, it allows easy
identiﬁcation of dubious arrivals, which are then removed. Following the removal of
spurious data, the data were again inverted for the determination of new origin times and

regional crustal velocity (Fig. 20). The origin times of most events were moved 0.2-0.3

32
data for all phases when plotted with the Pg relocations, I conclude that the 6.1 km/sec

Pg velocity used to determine locations listed in the Materialy catalog is too high.
Research by D. Gunbin (Personal communication, 1995) also indicates improved locations
when a slower crustal velocity of 6.0 km/5ec is used for the Magadan region.

The method of earthquake location used for most of the epicenters reported in
Materialy may also contribute to errors in the epicenters. Earthquakes in the Sakha
Republic (Y akutia) are still located by drawing arcs on large scale (approximately
1:8,000,000) paper maps. Considering the scale of the maps and thickness of the pencil
line being drawn, errors of several kilometers may be introduced into the location process.
These errors would probably be random with respect to azimuth.

In order to determine the ﬁrst-order crustal structure, the method of Ruff et al.,
(1994) ’SQUINT’ is used. This method assumes that regional travel time curves for
multiple earthquakes can be approximated with a regional average crustal model. Given
a set of earthquakes, the Pg travel time data are simultaneously inverted, solving for the
best ﬁt velocity for the set of events, and new origin times for individual events,
assuming ﬁxed hypocenters. For a given station, any systematic variation from the
regional average should be a result of local variations in crustal structure. The Pg data
was initially inverted with all spurious arrivals included (Fig. 19). Although this results
in an increase in data scatter compared with the non-inverted data, it allows easy
identiﬁcation of dubious anivals, which are then removed. Following the removal of
spurious data, the data were again inverted for the determination of new origin times and

regional crustal velocity (Fig. 20). The origin times of most events were moved 0.2-0.3

33

 

 

 

 

 

 

 

 

 

 

 

 

20
Vr= 6.00 km/s
A O X
3 'L .. ’8 Y
,:
A
X
+
0
-20 +
0. X (km) 1000.0
20
Vr= 8.00 km/s
X
L X
'— O
+
—20
0. X (km) 1000.0
Figure 19. Reduced traveltime curves for Pg (A) and Pn (B) data of selected best 75

events using relocated epicenters and origin times determined from the ’SQUINT’
inversion program. All data was included for this inversion trial. Individual events are
represented by different symbols.

20

34

 

 

 

Vr= 6.00 km/s

 

 

 

 

 

 

 

 

 

 

E Y
;
—20
0. X (km) 1000.0
20
Vr= 8.00 km/s
YX
A O Y X
(D J. >
v A x
,:
-;20
0. x (km) 15000
Figure 20. Reduced traveltime curves for Pg (A) and Pn (B) data of selected best 75

events. Epicenter relocations used are computed with Pg data, while origin times
determined from the ’SQUINT’ inversion program after high residual arrivals were
removed. These traveltime curves indicate a Pg velocity of 5.992 i 0.007 km/sec and a
Pn velocity of 7.961 1 0.015 km/sec. Reduction velocities are noted on ﬁgures.
Individual events are represented by different symbols.

35

seconds later from the origin time determined in the Pg relocation (Table l). The reason
for the consistent shifts in origin times is not clear, though may be related to incorrect
assumptions about source depth. Using the Pg relocation epicenter, the Pn data were also
inverted, ﬁrst for identiﬁcation of spurious arrivals (Fig. 19), which were subsequently
removed. The Pn data were again inverted to determine the regional Pn velocity.
Although inversion of the Pn data reveals nothing with respect to origin time, it does
allow the best determination of the regional Pn velocity. Knowledge of the regional Pn
velocity is necessary for the interpretation of the regional crustal structure.

As a result of this inversion the apparent velocities and crossover distance, and
thus approximate crustal thickness are obtained for the study area as a whole (Fig. 21).
Results for the Magadan region and Sakha Republic (Yakutia) indicate a Simple Structure
with a 5.992 1 0.007 kin/sec layer overlying a 7.961 i 0.015 km/Sec layer. Average
thickness is about 37 km Data at shorter epicentral distances (< 260 km) suggest a
slightly higher Pg velocity; the reason for this is likely related to rrrisidentiﬁcation of
phases at the crossover distance. This apparent slightly higher crustal velocity is visible
on the regional crustal travel time curve as a slight downwarp in the data (Fig. 20). I do
not believe this downwarp to be caused from a 6.7 km/sec intermediate layer as reported
by Ansimov et al. (1967). The existence of a 6.7 krn/sec refracting intermediate layer
should cause a signiﬁcant number of mispicked Pg and Pn phases at distances greater

than the crossover, which is not evident on any plotted traveltime curve.

35

seconds later from the origin time determined in the Pg relocation (Table 1). The reason
for the consistent shifts in origin times is not clear, though may be related to incorrect
assumptions about source depth. Using the Pg relocation epicenter, the Pn data were also
inverted, ﬁrst for identiﬁcation of spurious arrivals (Fig. 19), which were subsequently
removed. The Pn data were again inverted to determine the regional Pn velocity.
Although inversion of the Pn data reveals nothing with respect to origin time, it does
allow the best determination of the regional Pn velocity. Knowledge of the regional Pn
velocity is necessary for the interpretation of the regional crustal structure.

As a result of this inversion the apparent velocities and crossover distance, and
thus approximate crustal thickness are obtained for the study area as a whole (Fig. 21).
Results for the Magadan region and Sakha Republic (Yakutia) indicate a simple structure
with a 5.992 1: 0.007 kin/sec layer overlying a 7.961 i 0.015 km/sec layer. Average
thickness is about 37 km. Data at shorter epicentral distances (< 260 km) suggest a
slightly higher Pg velocity; the reason for this is likely related to rrrisidentiﬁcation of
phases at the crossover distance. This apparent slightly higher crustal velocity is visible
on the regional crustal travel time curve as a slight downwarp in the data (Fig. 20). I do
not believe this downwarp to be caused from a 6.7 km/sec intermediate layer as reported
by Ansimov et al. (1967). The existence of a 6.7 km/sec refracting intermediate layer
should cause a signiﬁcant number of mispicked Pg and Pn phases at distances greater

than the crossover, which is not evident on any plotted traveltime curve.

36

Table 1. New origin times for the selected best 75 events, computed by ’SQUINT’.
Relocation origin times from Pg phase relocations.

37

 

 

TABLE 1
DATE RELOCATION TIME NEW O.T.
O.T. SHIT-'1‘ (S)

81-02-02 19:15:15.5 +0.19 19:15:15.69
81-05-10 18:08:25.8 +0.28 18:08:26.08
81-11-08 21:56:08.9 +0.28 21:56:09.19
81-11-10 10:54: 15.5 +0.20 10:54: 15.70
81-11-11 14:22: 18.5 +0.22 14:22: 18.72
81-12-08 10:57:20.6 +0.26 10:57:20.86
82-04-06 14:41:13.9 -0.38 14:41: 13.52
82-08-04 20: 17:03.5 +0.27 20: 17:03.77
82-12-22 15:47:03.6 +0.22 15:47:03.82
83-03-12 11:55:11.7 +0.09 11:55: 1 1.79
83-03-25 10:36:55.1 +0.19 10:36:55.29
83-05-09 16:48:05.3 +0.29 16:48:05.59
83-10-25 19:44:59.9 +0.17 19:45:00.07
84-08-21 17:41:02.7 023 17:41:02.47
84-12-02 08:35:45.1 +0.35 08:35:45.45
84-12-02 18:17:54.9 +0.23 l8: 17:55.13
85-01-21 18:03:50.4 +0.25 18:03:50.65
85-01-24 20:26:33.2 +0.28 20:26:33.48
85-01-29 00:36:06.2 +0.02 00:36:06.22
85-03-08 22:24:37.8 +0.32 22:24:38. 12
85-06-02 04:08:08.8 +0.31 04:08:09.1 1
85-1 1-28 08:38:20.5 +0.20 08:38:20.70
86-01-18 13:13:22.0 +0.28 13:13:22.28
86-02- 15 20:30:26.3 +0.20 20:30:26.50
86-03-07 23:28:08.2 +0.23 23:28:08.43
86-04-06 01:27:20.5 +0.22 01:27:20.72
86-12-18 18:04:11.2 +0.27 18:04:11.47
86-12-26 03:21:04.5 +0.31 03:21:04.81
87-02-1 1 00:58: 19.8 +0.26 00:58:20.06
87-02-11 01:03:08.0 +0. 19 01:03:08.19
87-02-11 01:09:50.8 +0.28 01:09:51.08
87-02-11 06:19: 16.3 +0.40 06:19: 16.70
87-02-11 07:28: 17.5 +0.17 07 :28: 17.67
87-02-11 11:36:16.1 +0.19 11:36:16.29
87-03-04 00:09:28.0 +0.39 00:09:28.39
87-04-13 21:20: 12.8 +0.18 21 :20: 12.98
87-09-09 04:43:22.8 +0.30 04:43:23.10
88-02-19 00:04:04.0 +0.23 00:04:04.23
88-02-19 23:50:24.9 +0.18 23:50:25.08
88-04-03 02:01:28.6 +0.16 02:01:28.76
88-05-25 16:55:43.7 +0.05 16:55:43.75
88-06-09 13:37:32.9 +0.17 13:37:33.07
88-06—14 14:44:44.1 +0.24 14:44:44.34
88-10-17 00:27:59.2 +0.26 00:27 :59.46
89-01-29 23:23:01.6 +0.23 23:23:01.83
89-03-21 10:53:05.1 +0.16 10:53:05.26

89-04-09
89-06-16
89-07-07
89-07-09
89-10-04
90-03-29
90-05-30
90-06-25
90-07- 12
90-08-24
90-1 1-01
90-1 1-02
90-1 1-22
90-12-13
91-02-10
91-03-01
91-07-02
91-07-31
91-08-04
91-08-04
91-08-26
92-01-22
92-02- 12
92-06-28
92-1 1-17
93-03-05
93-03-22
93-03-24
93-08-30

04:16:23.0
07:36:08.5
10:51:43.1
18:11:49.0
20:56:47.2
20:47:29.7
1 1:56:45.l
07:33:51.7
02:22:50.5
01:04:44.6
13:42:06.1
21:54:03.2
19:36:25.1
21:34:39.1
18:16:32.3
01:57:04.1
13:43:45.0
01:44:02.7
10:08:05.9
19:14:40.6
09:35:49.0
06:29: 16.1
17:14:51.2
23:53: 17.4
07:55: 13.8
04:21:05.1
18: 14:06.8
16:18:05.9
07:56:34.9

38

Table 1 (continued)

+0.43
+0.16
+0.14
+0.21
+0.52
+0.1 1
+0.27
+0.21
+0.18
+0.28
+0.27
+0.3 1
+0.28
+0.26
+0.13
+0.38
+0.27
+0.32
+0.25
+0.17
+0.40
+0.33
+0.28
+0.23
+0.22
+0.20
+0.21
+0.27
+0.37

04: 16:23.43
07:36:08.66
10:51:43.24
18:1 1:49.22
20:56:47.72
20:47:29.81
1 l:56:45.37
07:33:51.91
02:22:50.68
01:04:44.88
13:42:06.37
21:54:03.51
19:36:25.38
21:34:39.36
18: 16:32.43
01:57:04.48
13:43:45.27
01:44:03.02
10:08:06.15
19: 14:40.77
09:35:49.40
06:29: 16.43
17:14:51.48
23:53: 17.63
07 :55: 14.02
04:21:05.30
18: 14:07.01
16:18:06.17
07:56:35.27

39

Figure 21. Reduced traveltime curve for combined Pg and Pn data All data plotted
use the Pg data relocated epicenter and origin times from the ’SQUINT’ inversion
program after high residual arrivals were removed. The Pg-Pn crossover point is
consistant with a regional crustal thickness of 37 km (Optically determined). Pg velocity
plotted is 5.99 km/sec, and Pn velocity is 7.96 kin/sec. Reduction velocities are noted on
ﬁgures. Individual events are represented by different symbols.

 

 

 

 

 

40

(8) Jr

1000.0

X (km)

Individual Stations

I next examined the travel time data for individual stations. A best-ﬁt crustal
structure was estimated based on travel time curves derived from relocated epicenters and
inverted origin times. Best-ﬁt lines to the data were determined optically. The use of
seventy ﬁve events in the analysis results in a lack of data at some outlying stations, and
thus poorer detenninations of velocities and crustal thickness. This primarily affects the
stations in northern Yakutia. This problem is more serious for the mantle refraction, Pn.
Sufﬁcient data were available for 27 stations, and present data suggests that structural
variations between stations in the study area are resolvable with this method. Based on
final results, the errors in determining crustal thickness appear to be i4-5 km, Pg
velocities, $0.03 kin/sec, and Pn velocities, $0.1 km/sec. In general, Sg velocities appear
to be 3.5 $0.04 kin/sec, while Sn velocities are generally unobtainable. There is some
trade off between Pn velocity and crustal thickness; higher velocities usually result in
greater thicknesses. The use of a computer data-ﬁtting routine will improve these
determinations. The use of additional data, particularly from outlying regions would also
improve the crustal parameter determinations.

The results (Tables 2 and 3) suggest that velocities and thicknesses are very close
to those determined to be the regional average. Most stations are ﬁt well with a 6.00
km/sec Pg velocity, a 7.99 km/sec Pn velocity, and a 37 km depth. Magadan (Fig. 22)
and Takhtoyamsk (Fig. 23) appear to have greater thicknesses of 40 km, although both

are constrained by a small number of observations. Signiﬁcantly, both of these stations

41

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42

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43

Table 3

PN AND PG VELOCITIES

 

Station Pg Pn Pn

This Study This Study Suvorov and
Kornilova (1986)

Batagai 5.97 7.94 8.1

Debin 5.99 7.97

Evensk 6.01 8.07

Khandyga 6.00 8.10 8.1-8.2

Kulu 5.98 7.73

Magadan 6.01 8.00

Moma 6.03 7.98 8.1

Myakit 5.99 7.90

Naiba 5.96 7.70

Nelkoba 5.97 7.87

Nezhdaninskoe 5.98 7.98

Omolon 5.98 7.98

Omsukchanl 5.99 8.00

Saidy 6.01 8.04

Sasyr 5.98 8.00

Seimchan 5.98 8.00 7.9-8.1

Sinegore 6.00 8.00

Stekolnyi 5.98 8.04

Susuman 6.00 7.96 7.9-8.0

Tabalakh 6.01 7.94

Takhtoyamsk 6.02 8. 10

Talaya 5.96 8.10

Tenkeli 5.98

Ust’ Nera 5.99 7.95 8.0-8.1

Ust’ Omchug 6.05 7.90 7.9-8.1

Yakutsk 6.03 8.00

Yubileinaya 5.96 7.49

Zyryanka 5.98 8.22

REGIONAL 5.99 8.00

1 Mishin and Dareshkina (1966) calculated a Pg velocity for Omsukchan of 6.02 km/sec
by the method of Gaiskii.

 

 

 

 

 

 

 

 

 

 

 

 

4O Vr= 8.00 km/s
3’3
,:
Y
O
0. X (km) 750.0

40 .40 km/s
3
.:

+

45
O 0

Figure 22. Magadan station traveltime curves and crustal model. Upper plot shows
Pg and Pn data with velocities of 6.01 km/sec and 8.00 km/sec respectively. The Pg-Pn
crossover point is consistent with a crustal thickness of 40 km. Lower plot shows S g and
Sn data Sg data is best ﬁt with a velocity of 3.50 km/sec. No attempt was made to ﬁt
Sn data. All velocities and crustal thickness were ﬁt optically. Reduction velocities are
noted on ﬁgures. Individual events are represented by different symbols.

45

 

 

 

 

 

 

 

 

 

4O Vr= 8.00 km/S
3
,:
x J
+ o
0
0. x (km) ' 750.0
40 Vr= .40 km/s
X
33
F .
O )1
A
O
0. x (km) 7500

Figure 23. Takhtoyamsk station reduced traveltime curves and crustal model. Pg
velocity 6.02 km/sec, Pn velocity 8.10 km/sec, and crustal thickness 40 km. S g velocity
3.47 km/sec. Conventions as in Figure 22.

46
are located on the southern edge of the Okhotsk-Chukotka volcanic belt. In the region

of Magadan and Takhtoyamsk, the Okhotsk-Chukotka volcanic belt overlies the Kony-
Murgal terrane. The Kony-Murgal terrane is composed primarily of an accreted sequence
of island arc volcanic, plutonic, and related sedimentary rocks dating from Late Jurassic
to Early Cretaceous (Nokleberg et al., 1994; Watson and Fujita, 1985). Results are also
in good agreement with the deep seismic sounding results from the upper Yama River
valley, also near this suture, reported by Bobrobnikov and Izmailov (1989). By
extrapolation of the Magadan-Ust’ Srednikan DSS proﬁle, the crustal thickness at
Magadan is estimated to be approximately 30 km (Davydova et al., 1968; Ansimov et el.
1967; Suvorov and Kornilova, 1986). However, Magadan is located on a separate terrane
from the area actually covered by DSS proﬁles, and no data is available directly under
Magadan. Therefore, it may not be a valid assumption to extrapolate for crustal thickness
and velocities. It should be noted that for both Magadan and Takhtoyamsk, the Pn data
are sparse or scattered, with only one or two points controlling Pn velocity and crustal
thickness. Both crustal thickness and Pn velocity could be affected significantly by
alteration of only one data point in each plot The Pg data for Magadan and
Takhtoyamsk ﬁt well with velocities of 6.01 km/sec and 6.02 km/sec respectively. There
is no clear evidence in the data to support a 6.7 km/sec lower crust as observed along the
Magadan - Ust’ Srednikan proﬁle (Ansimov et al., 1967).

Stekolnyi is located approximately 70 km north of Magadan within the Viliga
terrane. This terrane consists primarily of a thick section of Carboniferous, Permian,

Triassic, and Jurassic marine elastic rocks with some intermixed volcanics (Nokleberg et

47
al., 1994). This study derives a crustal thickness of 37 km for Stekolnyi, with Pg and Pn

velocities of 5.98 km/sec, and 8.04 km/sec respectively (Fig 24). S wave data are ﬁt well
with Sg and Sn velocities of 3.48 km/sec and 4.6 km/sec, with a crustal thickness of 38
km The Sn data show considerable scatter, thus the Sn velocity and thickness are
unreliable. The crustal thickness here is in good agreement with the P-Ps conversion study
by Belyaevsky and Borisov (1974), which indicates a 37 km thick crust. The thickness
determined in this study is a bit higher than the 31-32 km indicated by the DSS line. The
data for Stekolnyi are considered good, as the velocities are constrained by many points.

To the north of Stekolnyi, within the Viliga terrane, are the stations Debin,
Myakit, Omsukchan, Seimchan, and Sinegor’e. These stations are all within a 200 km
radius, and are ﬁt well with a thickness of 37 km and Pg velocity of 5.98-6.00 km/sec
(Figs 25-29). Mishin and Dareshkina ( 1966) calculated a Pg velocity for Omsukchan of
6.02 km/sec using the "method of Gaiskii". Pn velocity is 8.00 km/sec for these stations,
with the exception of Myakit and Debin, where velocities are 7.90 km/sec and 7.97
km/sec respectively. Sg velocities are also well constrained at 3.52 km/sec for Seimchan
and Omsukchan and 3.50 km/sec for Debin. The scatter in the Debin Pn data are
considerable, while Myakit and Sinegor’e have Pn data over a short epicenn‘al distance,
thus Pn velocities have large error bars. For both Seimchan and Omsukchan, the
velocities and thickness are well constrained. There are no previous velocities or
thickness reported for Sinegor’e or Myakit, and only Belyaevsky (1974) reports a
thickness for Debin, at 43 km. Bobrobnikov and Izmailov (1979) believe the 43 km

ﬁgure for Debin to be in error. Previous determinations for crustal thickness at

48

 

 

 

 

 

 

 

 

 

 

750.0

4
O Vr= 8.00 km / s
E
;
0
0. X (km) 750.0
40 Vr= 240 km / s
X
A 0
Y
Xx 5
A +
i”.
L Y
1— o o 9
X X b;
X
Y )1
O 9
0
0. X (km)
Figure 24. Stekolnyi station reduced traveltime curves and crustal model. Pg velocity

5.98 km/sec, Pn velocity 8.04 km/sec, and crustal thickness'37 km. Sg velocity 3.48

km/sec. Conventions as in Figure 22.

49

 

 

 

 

 

750.0

 

 

 

 

750.0

40
Vr= 8.00 km/s
X
3
; O
A A Y a:
9 X 9 O
0
0. X (km)
40
Vr= K . O km/s
X
Y O
I“? 'X 9 x Y
V A.. ~30 A
2 «0 x
' DA ‘ o a
X 0 3‘ ﬂ
0
0. X (km)
Figure 25. Debin station reduced traveltime curves and crustal model. Pg velocity

5.99 km/sec, Pn velocity 7.97 km/sec, and crustal thickness 37 km. Sg velocity 3.50
km/sec. Conventions as in Figure 22.

50

 

40

Tr (s)

Vr= 8.00 km/s

 

 

 

 

X (km)

750.0

 

4O

Tr (s)

 

 

 

 

X (km)

750.0

Figure 26. Myakit station reduced traveltime curves and crustal model. Pg velocity
5.99 ansec, Pn velocity 7.90 km/sec, and crustal thickness 37 km. Sg velocity 3.50

km/sec. Conventions as in Figure 22.

51

 

 

 

 

 

 

 

 

 

 

 

4O Vr= 8.00 km/s
3
.2
0
0. X (km) 750.0
40 V5= 4. 5 km/s
)1
x 0
x
. o
3 OcY x
,t
0 ° 0 O x
—5
0. X (km) 750.0
Figure 27. Omsukchan station reduced traveltime curves and crustal model. Pg

velocity 5.99 km/sec, Pn velocity 8.00 km/sec, and crustal thickness 36.5 km. S g velocity
3.52 km/sec. Conventions as in Figure 22.

pm: tr

rU\ Lb

52

 

 

 

 

 

 

 

 

 

40 Vr= 8.00 km/s
Y
A P
."3
.2
x o
3 .
0 xx
0
0. X (km) 750.0
40
Vr= 4.’ m/s
0 W
x‘8 '
0
A X
£3 x ,g
.: A: °
0 "e.
+
A .
+
0
0. X (km) 750.0
Figure 28. Seimchan station reduced traveltime curves and crustal model. Pg velocity

5.98 km/sec, Pn velocity 8.00 km/sec, and crustal thickness 37 km. Sg velocity 3.52

km/sec. Conventions as in Figure 22.

 

4C

(*3)

T r

(S)

Ir

Figu
km/s

53

 

4O

Tr (s)

Vr= 8.00 km /s

 

 

 

 

 

 

750.0

 

4O

Tr (3)

0x
0

 

Vr= - .40 km/s

 

 

0. - X (km)

750.0

Figure 29. Sinegor’e station reduced traveltime curves and crustal model. Pg velocity
6.00 km/sec, Pn velocity 8.00 km/sec, and crustal thickness 37 km. Sg velocity 3.53

km/sec. Conventions as in Figure 22.

54
Omsukchan range from 30 km (Belyaevsky, 1974) to 38 km (Suvorov and Kornilova,

1986). The thickness determination for Omsukchan in this study falls in between at 36.5
km. For Seimchan, this study determines the thickness to be 2-3 km greater than
previous studies. For this study, I estimate crustal thickness errors for Seimchan and
Omsukchan to be 2 km. Bulin (1989) has also determined this region of the study area
to have a homogeneous crustal structure, which is consistent with my results.

Talaya may also ﬁt within this homogeneous region, although Pg and S g velocities
for Talaya are lower than the above discussed region at 5.96 km/sec and 3.48 km/sec,
respectively, both being fairly well constrained (Fig. 30). A crustal thickness of 38 km
is calculated for Talaya, although Pn data are sparse. This crustal thickness would be
consistent with a thickening of the crust toward the south, as indicated by Magadan and
Takhtoyamsk.

The area immediately east of the homogeneous region discussed above contains
Kulu, Susuman, Nelkoba, and Ust’ Omchug stations, all showing a slightly reduced
crustal thickness (Figs. 31-34). Crustal thicknesses range from 30 km at Susumam to 35
km at the other stations. In addition, all stations indicate reduced Pn velocities ranging
from 7.73 krn/sec at Kulu to 7.96 km/sec at Susuman. For these stations, there is no
consistent velocity change for either Pg or Sg phases. It should be noted that values for
Ust’ Omchug have large error bars due to limited data. The previous estimates of crustal
thickness for Ust’ Omchug are 29 km by Suvorov and Kornilova (1986), and an estimate
of 36 km from the Magadan-Ust’ Srednikan proﬁle. Previous estimates for Susuman are

inconsistent, with values ranging from 33 km (Suvorov and Kornilova, 1986) to 50 km

 

(J?

55

 

 

 

 

 

 

 

 

 

4O Vr= 8.00 km/s
3
p‘.‘
+ x a A
O
40
Vr= .40 km/s
x
”(n7
v X
,:
A .
O
O. X (km) 750.0

Figure 30. Talaya station reduced traveltime curves and crustal model. Pg velocity
5.96 km/sec, Pn velocity 8.10 km/sec, and crustal thickness 38 km. Sg velocity 3.48
km/sec. Conventions as in Figure 22.

$1!

56

 

40
Vr= 8.00 km/s

Tr (s)

 

 

 

 

 

 

 

 

0. X (km) 780.0

 

4O

Tr (s)

 

 

 

 

 

O. X (km) 750.0

Figure 31. Kulu station reduced traveltime curves and crustal model. Pg velocity
5.98 km/sec, Pn velocity 7.73 km/sec, and crustal thickness 30 km. Sg velocity 3.48
km/sec. Conventions as in Figure 22.

57

 

 

 

 

 

 

 

 

 

 

4O Vr= 8.00 km/s
3
f;
0
0. X (km) 750.0
40 Vr= .40 km/s
)1
)1 Y
6 0"
A
3 .
.9
5 O r 3
o ‘l‘ x
0“
0 )6“
A
0
O )1
0. X (km) 750.0
Figure 32. Susuman station reduced traveltime curves and crustal model. Pg velocity

6.00 kin/sec, Pn velocity 7.96 km/sec, and crustal thickness 35 km. Sg velocity 3.47
km/sec. Conventions as in Figure 22.

 

4C

(«3.)

lr

'5)

(

fr

Flgur

600

57

 

4O

Tr (s)

Vr= 8.00 km/s

 

 

 

 

 

 

 

 

 

750.0

0
4
O Vr= .40 km/s
x
6
.A ‘
. 9
.: ° «*3
x
s". . oA
. O o x+
A
o
O x
O. X (km)

Figure 32. Susuman station reduced traveltime curves and crustal model. Pg velocity
6.00 km/sec, Pn velocity 7.96 km/sec, and crustal thickness 35 km. Sg velocity 3.47

km/sec. Conventions as in Figure 22.

rﬁ

58

 

4o

Tr (s)

Vr= 8.00 km/s

 

 

 

 

 

750.0

 

4O

Tr (s)

 

 

 

 

750.0

Figure 33. Nelkoba station reduced traveltime curves and crustal model. Pg velocity
5.97 km/sec, Pn velocity 7.87 km/sec, and crustal thickness 35 km. Sg velocity 3.50

km/sec. Conventions as in Figure 22.

59

4O

 

Vr= 8.00 km/s

Tr (s)

 

 

 

 

 

 

 

 

 

 

 

 

 

o
O. . X (km) 750.0
40
$
.:
o
0- X (km) 750.0

Figure 34. Ust’ Omchug station reduced traveltime curves and crustal model. Pg
velocity 6.05 km/sec, Pn velocity 7.90 km/sec, and crustal thickness 35 km. Sg velocity
3.51 km/sec. Conventions as in Figure 22.

to in
igno

SU'UC

the I
36).
at 3.
6.03
Ncr.
set 1
of C
no ]
thic
und

The

blot
The

Nor

6O
(Belyaevsky, 1974). Given the 2 km difference between the Suvorov and Kornilova

estimate and my estimate, I believe the Belyaevsky (1974) estimate to be in error.
Previous studies on Nelkoba indicate a thickness of 39-40 km. It is not possible for me
to increase crustal thickness by the required 4-5 km to agree with previous studies without
ignoring a signiﬁcant portion of my data. No previous studies have considered the crustal
structure at Kulu.

Ust’ Nera and Moma (Khonu) are located to the northwest of Susuman, continuing
the trend of a slightly elevated Moho at 35 km and reduced Pn velocities (Figs. 35 and
36). For Ust’ Nera, Pn velocity is 7.95 km/sec, with Pg velocity at 5.99 km/sec and Sg
at 3.53 km/sec. For Moma, Pn velocity is 7.87 km/sec, while Pg and Sg velocities are
6.03 km/sec and 3.55 kin/sec respectively. Previous estimates of crustal thickness at Ust’
Nera range from 24 km (Suvorov and Kornilova, 1986) to 40 km (Bulin, 1989). The data
set for Ust’ Nera is one of the best in terms of epicentral distance coverage, and scatter
of data are acceptable, thus I feel the 35 km crustal thickness is reasonable. There are
no previous velocity or thickness determinations for Moma. The slightly reduced crustal
thickness and reduced Pn velocity are consistent ‘with a region which has recently
undergone an extensional event, and thus may represent a relic of the Moma rift system.
The station at Moma is within the Moma rift proper, as deﬁned by Fujita et al. (1990a).
Although this region is presently under compression, caused by extrusion of the Okhotsk
block (Riegel et al., 1993; Cook et al., 1986) the region was recently under extension.
The transition from extension to compression occurred as a result of the migration of the

North American-Eurasian pole to the north as recently as 0.5 Ma (Cook et al., 1986).

 

A

I

Nev

t...

A

JV

FlgL

5.99

61

 

4O

Vr= 8.00 km/S

 

 

 

 

 

 

 

 

 

 

 

:—
O

O. X (km) 750.0
45
3
,:
O.

o. x (km) 750.0

Figure 35. Ust’ Nera station reduced traveltime curves and crustal model. Pg velocity
5.99 km/sec, Pn velocity 7.95 km/sec, and crustal thickness 34 km. Sg velocity 34
km/sec. Conventions as in Figure 22. '

 

Tr (S)

Tr (S)

Figure
6.03 k
WC

62

 

4O Vr= 8.00 km/s

Tr (s)

 

 

 

 

 

 

750.0

 

4O

Tr (s)

 

 

 

 

 

o. x (km) 750.0

Figure 36. Moma station reduced traveltime curves and crustal model. Pg velocity
6.03 kin/sec, Pn velocity 7.87 km/sec, and crustal thickness 35 km. Sg velocity 3.55

km/sec. Conventions as in Figure 22.

Given

miles

an inc
38).

veloc
(1989

Zm'a

Baug
portit
ct al..
by T

Show

a [hit

Naib-

63

Given the recent transition to compression, the former extensional regions may still be
reﬂected in an elevated Moho and reduced Pn velocity.

Northeast from Ust’ Nera are stations Sasyr’ and Zyryanka. Both stations show
an increased crustal thickness, at 37 km for Sasyr’, and 47 km for Zyryanka (Figs. 37 and
38). Velocities are close to regional averages with the exception of an 8.22 km/sec Pn
velocity at Zyryanka Station Sasyr’ has been considered in previous studies. Bulin
( 1989) reports a thickness of 41 km for Ugol’naya (Zyryanka), and a thickness at
Zyryanka of 35-45 km is possible (Suvorov and Kornilova, 1986).

Continuing northwest along the trend of thinner crust, are the stations Tabalakh,
Batagai, and Saidy. Saidy is within the region encompassed by the Toustakh graben, a
portion of the Moma rift, while Batagai and Tabalakh lie immediately to the south (Fujita
et al., 1990a). Of the three stations, Batagai shows the thinnest crust at 32 km, followed
by Tabalakh at 34 km and Saidy at 35 km (Figs. 39-41). Both Batagai and Tabalakh
show reduced Pn velocities of 7.94 km/sec while Saidy has an elevated velocity of 8.04
km/sec. Compared to Batagai and Tabalakh, Saidy shows a higher Pn velocity and
slightly thicker crust.

Stations Naiba and Yubileniya are in the northern portion of the study area. Naiba
is located on Buor Khaya Bay, off the Laptev Sea, and Yubileniya is approximately 100
km south of the Laptev sea along the Yana river. The crustal thickness determinations
for these stations are among this study’s most interesting results. The Naiba data indicate
a thin crust at 29 km, with a reduced Pn velocity of 7.70 km/sec (Fig. 42). Geologically,

Naiba is located on the western edge of the Omoloi basin, the southern extension of the

 

 

 

 

 

 

 

 

 

 

750.0

40 Vr= 8.00 km/s
3

;

O

O. X (km) 750.0
40
Vr= 4. 2 m/s
3’}
t: o-
O
.0 Y

O

‘ O. X (km)

Figure 37. Sasyr’ station reduced traveltime curves and crustal model. Pg velocity

5.98 km/sec, Pn velocity 8.00 km/sec, and crustal thickness 37 km. Sg velocity 3.52

km/sec. Conventions as in Figure 22.

 

 

4O

Tr (s)

Vr= 8.00 km /s

 

 

 

 

 

 

 

 

 

750.0

0
O. X (km) 750.0
40
Vr= 4. 9 m/s

3

: o -

O
o. _ Y
O
O. X (krn)
Figure 37. Sasyr’ station reduced traveltime curves and crustal model. Pg velocity

5.98 km/sec, Pn velocity 8.00 km/sec, and crustal thickness 37 km. Sg velocity 3.52

km/sec. Conventions as in Figure 22.

 

 

40

(S)

Tr

L_)

40

(S)

Tr

FTOU
5.93

65

 

 

 

 

 

 

 

 

 

 

750.0

4
O Vr= 8.00 km/s
3
,:
O
O. X (km) 750.0
40 Vr= 4 km/s
Y
”a " +°"
I: +°
00"
0+ A
Y Y x
O
O. X (km)

Figure 38. Zyryznka station reduced traveltime curves and crustal model. Pg velocity
5.98 km/sec, Pn velocity 8.22 km/sec, and crustal thickness 47 km. Sg velocity 3.50

km/sec. Conventions as in Figure 22.

66

4O

 

Vr= 8.00 km/s

Tr (s)

 

 

 

 

 

 

 

 

 

O
o. x (km) 750.0
40
Vr= 4.40 m/s
0 0
v
0 o
X +
A x” Y
3; ..
L I!
*- o
o
x .
O
O
o. x (km) 750.0

Figure 39. Tabalakh station reduced traveltime curves and crustal model. Pg velocity
6.01 km/sec, Pn velocity 7.94 km/sec, and crustal thickness 34 km Sg velocity 3.53
km/sec. Conventions as in Figure 22.

 

4O

Amv up

Amv :

67

 

4O

Vr= 8.00 km/s

 

 

 

 

 

 

 

 

 

 

750.0

3
;
O
O. X (km) 750.0
40
Vr= 4.0. m/s
9
)9 0
° +
A O O
(D
v Y
t:
x
‘P o
+
O
i O. X (km)

Figure 40. Batagai station reduced traveltime curves and crustal model. Pg velocity
5.97 km/sec, Pn velocity 7.94 km/sec, and crustal thickness 32 km. Sg velocity 3.53

km/sec. Conventions as in Figure 22.

68

 

4O Vr= 8.00 km/s

 

 

 

 

 

 

 

 

 

3
,:
O
o. x (km) 750.0
40 Vr=+ 4.’ m/s
A
0 A Y
‘8
A A
3
p:
0X
9 o 0
q.
A o
O
o. x (km) 750.0

Figure 41. Saidy station reduced traveltime curves and crustal model. Pg velocity
6.01 km/sec, Pn velocity 8.04 km/sec, and crustal thickness 35 km. Sg velocity 3.52

km/sec. Conventions as in Figure 22.

69

 

 

 

 

 

 

 

 

 

 

 

 

 

 

750.0

40
Vr= 8.00 km/s
3
,:
O
o. x (km) 750.0
40 Vr= .40 km/s
33
,:
+
O
o. X (km)

Figure 42. Naiba station reduced traveltime curves and crustal model. Pg velocity
5.96 kin/sec, Pn velocity 7.70 km/sec, and crustal thickness 29 km. Sg velocity 3.47

km/sec. Conventions as in Figure 22.

7O
Omoloi graben (Fig. 4). This study shows Yubileniya to be located above a zone of

anomalously thin crust at 19 km (Fig. 43). For Yubileniya, Pn velocities are signiﬁcantly
reduced at 7.49 km/sec, while Pg velocities are near normal at 5.96 km/sec. Note that
the data supporting such a thin crust contains minimal scatter, and is not constrained by
any single point. Yubileniya is located in the southern end of the Ust’ Yana graben (Fig.
4). For both stations, local grabens from regional extension seem to be the controlling
factor in thinning of the crust. These stations indicate clear evidence of anomalously thin
continental crust in the southern portion of the Laptev rift system. Thin crust and low
Pn velocities are supported by DSS proﬁles in the south Laptev sea (Avetisov and
Guseva, 1991; Avetisov, 1983; Kogan, 1974). A reﬂection proﬁle 30 km east of Naiba
indicates a crustal thickness of approximately 28km (Avetisov and Guseva. 1991).

Located east of Yubileniya, station Tenkeli is located in the vicinity of Tenkeli
basin (Fig. 4), where an elevated Moho and reduced Pn velocity could be expected.
Unfortunately, Tenkeli results are inconclusive due to Pn data scatter and lack of close
in data. For Tenkeli, acceptance or rejection of a single datum can vary crustal thickness
from 24 km to 42 km (Fig. 44). Crustal velocity is constrained at 5.98 km/sec.

The southwest portion of the study area contains stations Yakutsk, Khandyga, and
Nezhdaninskoe. These stations are located within the eastern Siberian platform. These
stations evidence a generally thickened crust of 44 km at Khandyga, 39 km at
Nezhdaninskoe, and 38 at Yakutsk (Figs. 45-47). Pn velocities are near average, except
Khandyga where the Pn velocity is 8.10 km/sec. Pn velocity and crustal thickness are

poorly constrained for Yakutsk. Previous studies are in good agreement with these

 

(S)

 

Ir

('3

4S

Tr (S)

Cﬁ

Figur
ve10c.
3.54 J

71

 

40

Tr (s)

 

0

Vr= 8.00 km/s

 

 

o. . X (km)

820.0

 

45

Tr (s)

 

2" 4.40 km/s

 

 

 

 

X (km)

10000

Figure 43. Yubileniya station reduced traveltime curves and crustal model. Pg
velocity 5.96 km/sec, Pn velocity 7.49 km/sec, and crustal thickness 19 km. Sg velocity

3.54 kin/sec. Conventions as in Figure 22.

72

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

800.0

40
Vr= 8.00 km/s
3’3
,:
0
o. x (km) 800.0
4
O Vr= 4. m/s
9 X
0
o -
x
3
,:
+ X 4
+
o ‘1
-5
o. X (km)

Figure 44. Tenkeli station reduced traveltime curves and crustal model. Pg velocity
5.98 km/sec, Pn velocity 7.70 km/sec, and crustal thickness 24 km. Sg velocity 3.57

km/sec. Conventions as in Figure 22.

72

 

 

 

 

 

 

 

 

 

 

 

 

 

4O Vr= 8.00 km/s
E
t:
0
O. x (km) 800.0
40 Vr= 4- % [71/5
9 X
0
0
X
3
.:
+ X 9
+
o ‘-
—5
0. X (km) 800.0
Figure 44. Tenkeli station reduced traveltime curves and crustal model. Pg velocity

5.98 km/sec, Pn velocity 7.70 km/sec, and crustal thickness 24 km. Sg velocity 3.57
km/sec. Conventions as in Figure 22.

72

 

40

Vr= 8.00 km/s

 

 

 

 

 

 

 

 

 

 

 

3
,:
0
o. x (km) 800.0
40
Vr= 4 9 m/s
9 X
0
0
X
3
,:
+ X 9
+
o \u
-5
o. x (km) 800.0

Figure 44. Tenkeli station reduced traveltime curves and crustal model. Pg velocity
5.98 km/sec, Pn velocity 7.70 km/sec, and crustal thickness 24 km. Sg velocity 3.57
km/sec. Conventions as in Figure 22.

PE"

73

 

 

 

 

 

 

45 Vr= 8.00 km/S
37E
,:
A
0
0
0
0. X (km) 1500.0

 

75 .40 km/s

Tr (s)

 

 

 

 

 

X (km) 1500.0

Figure 45. Yakutsk station reduced traveltime curves and crustal model. Pg velocity 6.03
kin/sec, Pn velocity 8.00 km/sec, and crustal thickness 38 km. Sg velocity 3.52 km/sec.

Conventions as in Figure 22.

x

(Q)

Tr

73

 

45

Tr (s)

 

 

Vr= 8.00 km/s

 

 

 

 

 

 

 

 

0
0. x (km) 1500.0
75 .40 km/s
3
.:
\

—l

.5 1500.0

X (km)

Figure 45. Yakutsk station reduced traveltime curves and crustal model. Pg velocity 6.03
km/sec, Pn velocity 8.00 km/sec, and crustal thickness 38 km. Sg velocity 3.52 km/sec.

Conventions as in Figure 22.

Tr (s)

45

Tr (s)

Fig

74

 

40

Tr (s)

Vr= 8.00 km/s

 

 

 

 

 

750.0

 

45

Tr (s)

(b

Vr= 4.402km

 

 

 

 

750.0

Figure 46. Khandyga station reduced traveltime curves and crustal model. Pg velocity
6.00 km/sec, Pn velocity 8.10 km/sec, and crustal thickness 44 km. Sg velocity 3.51

km/sec. Conventions as in Figure 22.

(S)

Tr

 

 

 

 

C)

(S)

Tr

Fig
VCII

3.51

40

Tr (s)

50

Tr (s)

75

 

 

 

Vr= 8.00 km/s

 

 

 

X (km) . 750.0

 

 

 

 

 

 

 

 

 

 

 

 

x (km) 10000

Figure 47. Nezhdaninskoe station reduced traveltime curves and crustal model. Pg
velocity 5.98 km/sec, Pn velocity 7.98 km/sec, and crustal thickness 39 km. Sg velocity
3.50 km/sec. Conventions as in Figure 22.

(a)

Tr

C')

(.J_|

)

U.

(

Tr

Fig
VClt
3.5(

75

 

40

Tr (s)

 

Vr= 8.00 km/s

 

 

 

 

750.0

 

50

Tr (s)

 

 

 

 

 

 

 

 

 

 

0. X (km)

1000.0

Figure 47. Nezhdaninskoe station reduced traveltime curves and crustal model. Pg
velocity 5.98 km/sec, Pn velocity 7.98 km/sec, and crustal thickness 39 km. Sg velocity

3.50 km/sec. Conventions as in Figure 22.

SL

01

(N

“0]

V6]

76
results. Suvorov and Kornilova (1986) indicate a crustal thickness of 44 km at Khandyga,

40 km at Nezhdaninskoe, and 37 km at Yakutsk. However, data from their study indicate
somewhat higher Pn velocities. Neustroev and Parfenov (1985) have also calculated
crustal thicknesses for the eastern Siberian platform, indicating 42 km for Khandyga and
Yakutsk, and 40 km for Nezhdaninskoe. Bulin (1989) indicates a crustal thickness of 37
km for Nezhdaninskoe.

Evensk, on Shelikhov Bay, is located on the Avekova terrane. The Avekova
terrane is composed of Proterozoic gneiss, crystalline schist, and metamorphosed
carbonates. Younger units are primarily marine, with minor volcanics (Nokleberg et al.,
1994). Evensk data indicate a normal crustal thickness of 37 km, but slightly elevated
Pg and Pn velocities at 6.01 km/sec and 8.07 km/sec (Fig. 48). Sn velocities are slightly
below normal at 3.48 km/sec. Crustal thickness for Evensk is within 3 km of all other
determinations, falling near the center of the ﬁeld of previous values. There are no other
published velocities for Evensk, thus it is not possible to verify the slightly increased
velocities.

Omolon is located north of Evensk, near the center of the Kolyma-Omolon
superterrane (Nokleberg et al., 1994). Station Omolon lies on the Omolon block of the
Kolyma-Omolon superterrane. In this study, aside from stations on the Siberian Platform,
Omolon is probably the only station which lies on ancient Precambrian continental crust
(Nokleberg et al., 1994). Crustal data for Omolon are well constrained and indicated a
normal crustal thickness of 37 km, but slightly reduced P velocities (Fig. 49). A Pg

velocity of 5.98 km/sec and Pn velocity of 7.98 ﬁt the data well. A slightly reduced Sg

76
results. Suvorov and Kornilova (1986) indicate a crustal thickness of 44 km at Khandyga,

40 km at Nezhdaninskoe, and 37 km at Yakutsk. However, data from their study indicate
somewhat higher Pn velocities. Neustroev and Parfenov (1985) have also calculated
crustal thicknesses for the eastern Siberian platform, indicating 42 km for Khandyga and
Yakutsk, and 40 km for Nezhdaninskoe. Bulin ( 1989) indicates a crustal thickness of 37
km for Nezhdaninskoe.

Evensk, on Shelikhov Bay, is located on the Avekova terrane. The Avekova
terrane is composed of Proterozoic gneiss, crystalline schist, and metamorphosed
carbonates. Younger units are primarily marine, with minor volcanics (Nokleberg et al.,
1994). Evensk data indicate a normal crustal thickness of 37 km, but slightly elevated
Pg and Pn velocities at 6.01 km/sec and 8.07 km/sec (Fig. 48). Sn velocities are slightly
below normal at 3.48 km/sec. Crustal thickness for Evensk is within 3 km of all other
determinations, falling near the center of the ﬁeld of previous values. There are no other
published velocities for Evensk, thus it is not possible to verify the slightly increased
velocities.

Omolon is located north of Evensk, near the center of the Kolyma-Omolon
superterrane (Nokleberg et al., 1994). Station Omolon lies on the Omolon block of the
Kolyma-Omolon superterrane. In this study, aside from stations on the Siberian Platform,
Omolon is probably the only station which lies on ancient Precambrian continental crust
(Nokleberg et al., 1994). Crustal data for Omolon are well constrained and indicated a
normal crustal thickness of 37 km, but slightly reduced P velocities (Fig. 49). A Pg

velocity of 5.98 km/sec and Pn velocity of 7.98 ﬁt the data well. A slightly reduced Sg

77

 

40

Tr (s)

 

 

 

 

 

0
x (km) 1000.0

 

45

Tr (s)

 

 

 

 

 

0. x (km) 750.0

Figure 48. Evensk station reduced traveltime curves and crustal model. Pg velocity
6.01 km/sec, Pn velocity 8.07 km/sec, and crustal thickness 37 km. Sg velocity 3.48

km/sec. Conventions as in Figure 22.

78

 

 

 

 

 

 

 

 

 

 

 

4O
3
t:
0
O X (km) 1000.0
50 Y
+ = 4.40 km / s
9
0
0
° +

A )1 Y O

33

L +

.—

e
x Y
X
—5
0. X (km) 1000.0

Figure 49. Omolon station reduced traveltime curves and crustal model. Pg velocity

5.98 krn/sec, Pn velocity 7.98 km/sec, and crustal thickness 37 km. Sg velocity 3.47
km/sec. Conventions as in Figure 22.

79
velocity of 3.47 km/sec is also observed for Omolon. Crustal thickness for Omolon is

in agreement with previous studies, where values of 38-40 km have been determined.
All crustal thickness values determined in this study are plotted and contoured in
ﬁgure 50. As a consequence of these results, it is apparent that additional data is
necessary for some stations, while for other stations additional work to eliminate spurious
and misidentiﬁed phases would be beneﬁcial. For all stations, it will be necessary in the
future to obtain better quantitative ﬁts to the data. However, this method does appear to

be able to resolve variations in crustal and upper mantle velocities and crustal thicknesses.

Discussion

The Pn and Pg velocities obtained herein generally indicate a thicker crust and
lower velocity upper mantle than the results of the Magadan-Ust’ Srednikan refraction
line (Davydova et al., 1968; Ansimov et al., 1967; Belyaevsky, 1974). In comparison with
the analysis of Suvorov and Kornilova (1986; Fig. 6), an interesting pattern develops. For
individual stations, results are either in good agreement with Suvorov and Kornilova
(1986), within 2 km, or not, being 6 km to 10 km greater. All stations where crustal
thicknesses determined in this study are 6 km or greater than those of Suvorov and
Kornilova (1986) fall along a north-west-north trend from Magadan. Results for stations
to the northeast of this trend (Omsukchan, Seimchan, and Susuman) are in excellent
agreement with Suvorov and Kornilova (1986). To the southwest, stations Yakutsk,
Khandyga, and Nezhdaninskoe, are also in good agreement with values by Suvorov and

Kornilova (1986). In general, the trend follows the region where the crust is thinnest in

8O

 

 
  
  

 

 

 

 

 

 

 

130 140 150 160
SOT
La tev Sea . .
l? 1) East - Siberian Sea
3 TIK
?°
'AY
KYU '2 l9 YUB
. , / /
\ fr
‘9;
at
SAY 35 3%
BTG 3 _ .
32 AT-
\
\
\
KHG .4
YAK >
4%“) 3
. l
‘CGD
Sea of Okhotsy

 

 

 

Figure 50. Summary of crustal thickness determinations for the study area. Contour
interval = 5 km. Note the generally thinner crust extending northwest from station Ust’
Omchug (USO). This region of thinner crust corresponds to the seismically active region
and boundary between the North American and Eurasian plates. The thinned crust in this
region may have resulted from a Cenozoic rifting episode. Station codes as in ﬁgure 7.

81

both studies. This trend is likely the result of the systematically mislocated epicenters
used by Suvorov and Kornilova (1986). The associated errors appear to be about half that
of Suvorov and Kornilova (1986). In addition, Suvorov and Kornilova (1986) assumed
the thickness at Magadan using the refraction line, however as noted above, this result
should be applied at Stekolnyi. Upper mantle velocities are generally slightly less, but
are in agreement between this study and Suvorov and Kornilova (1986). Speciﬁcally, the
highest Pn velocity determined in both studies study was at Khandyga (Table 1). The
crustal thicknesses also agree fairly well with those reported by Belyaevsky and Borisov
(1974) for Stekolnyi, Magadan, Omolon, and Omsukchan. Their value for Magadan lends
some support for a thicker crust in the Okhotsk-Chukotka volcanic belt. Overall,
Khandyga, Nezhdaninsk, Yakutsk, and perhaps Omolon show the most consistent
agreement among multiple studies. Thus, the degree of conﬁdence for stations in older
platform regions is high.

The major differences between the various determinations are for Ust’ Nera,
Magadan, and Nelkoba. Nelkoba data indicates a thickness 4 km to 6 km thinner than
that determined by P-Ps conversions (Mishin and Dareshkina, 1966; Belyaevsky and
Borisov, 1974; Vaschilov, 1989). Nelkoba and Magadan both have a high degree of
scatter in the Pn data, thus it is possible to vary the crustal structure model to conform
with other studies and still maintain a reasonable ﬁt to the data. The situation at Ust’
Nera is more problematic. There is a great difference in the crustal thickness reported
at Ust’ Nera by Suvorov and Kornilova (1986), 24 km, and by Bulin (1989), 40 km. Our

results fall somewhat in between at 34 km. Although there is some scatter in the Pn data,

82
a crust signiﬁcantly thicker or thinner can not be supported. Thus, the author is inclined

to disagree with the results of Suvorov and Kornilova (1986), and Bulin (1989). Gravity
analysis by Norton et al. (1994) also suggest a crustal thickness near Ust’ Nera of 35-36
km, supporting a slightly thinned crust relative to the regional average.

The overall general trend for crustal thicknesses determined in this study support
a slightly thinner crust throughout the central Chersky seismic belt (Fig 50). Throughout
most of the Chersky seismic belt, the crustal thickness variations are generally less than
4 km. This may imply that the effects of the Moma rift are less than envisioned by
Parfenov et al. (1988) and Lander (1984). This study does indicates significant crustal
thinning in the southern portions of the Laptev Sea rift. The basic trend is identical to
that identiﬁed by Suvorov and Kornilova (1986), except lesser in degree. Converted wave
studies are not clearly supportive of this trend.

Gravimetric data are available for the central and northern portion of the study
area (Fig. 51; Parfenov et al., 1988; Crumley and Parfenov, 1994). The central portion
of the study area shows some correlation with the gravity data. The region of thinned
crust corresponds roughly with large negative anomalies, although crustal thickness
contours here are constrained by only a few data points. Large negative anomalies do not
correlate well with the thinned crust in the northern Laptev Sea rift portion on the study
area. The lack of good correlation between gravity anomalies and crustal thickness attests
to the difﬁculty of determining crustal thickness solely with gravity data as in studies by
Vaschilov (1984), and Bobrobnikov and Izmailov (1989).

The locations of elevated heat flow levels (Fig. 52) are generally consistent with

83

 

INCREASE OF GRAVITY ANOMALIES

 

 

l l l l\\\ ' 1312815.

 

Figure 51. Map of relative gravity anomalies for the nonhem and central portion of
the study area. From Parfenov et al.(1988).

84

155 160

 

Siberian Sea

 

70

 

 

«6’3”

’9 6S

 

 

 

 

 

 

 

 

 

 

 

 

 

 

\
\
m

 

Figure 52. Map of heat ﬂow levels in the study area. Triangles represent borehole
locations with values in mW/mz. Values in brackets were interpolated from contours on
other maps.

85
the region of thinned crust. Within the thinned crust region, heat flow reaches a

maximum of 84 mW/m2 at Ust’ Nera (Melnikov et al., 1976). At Zyryanka, to the
northeast of Ust’Nera, heat ﬂow drops to 56 mW/m2 (Duchkov et al., 1982; Duchkov and
Sokolova, 1985). To the southwest, there is a slight increase in heat ﬂow to 100 mW/m2
at Nezhdaninskoe (Parfenov, 1988), and then a rapid decline to 42 mW/m2 near Yakutsk
and less than 30 mW/m2 just beyond (Duchkov et al., 1982; Koz’min et al., 1994). The
regions of elevated heat ﬂow are likely remnants of the extensional episode which formed
the Moma rift. However, it is puzzling that heat ﬂow values in the Laptev Sea rift
region, on an active rift, do not appear elevated as would be expected. Reported heat
ﬂow measurements may be affected by extremely thick permafrost layers (>500m), which
in some cases is as deep as the boreholes used in the heat ﬂow measurements penetrate
(Melnikov et al., 1976). It should be noted that the actual boundaries of the elevated heat

flow region are difﬁcult to constrain with the available data.

Conclusions
The method of Ruff et al. (1994) allows one to obtain corrections in origin time
and timing errors and allows rapid identiﬁcation of spurious arrivals reported in the
Russian bulletins. Combined with relocations of epicenters, this method has allowed the
reﬁning of the ﬁrst-order crustal structure of northeast Russia using available phase data
and the investigation of crustal thickness and upper mantle velocities at individual

stations. This work conﬁrms that a simple crustal model is a superior method of locating

85

the region of thinned crust. Within the thinned crust region, heat ﬂow reaches a
[maximum of 84 mW/m2 at Ust’ Nera (Melnikov et al., 1976). At Zyryanka, to the
northeast of Ust’Nera, heat ﬂow drops to 56 mW/m2 (Duchkov et al., 1982; Duchkov and
Sokolova, 1985). To the southwest, there is a slight increase in heat ﬂow to 100 mW/m2
at Nezhdaninskoe (Parfenov, 1988), and then a rapid decline to 42 mW/m2 near Yakutsk
and less than 30 mW/m2 just beyond (Duchkov et al., 1982; Koz’min et al., 1994). The
regions of elevated heat flow are likely remnants of the extensional episode which formed
the Moma rift. However, it is puzzling that heat ﬂow values in the Laptev Sea rift
region, on an active rift, do not appear elevated as would be expected. Reported heat
ﬂow measurements may be affected by extremely thick permafrost layers (>500m), which
in some cases is as deep as the boreholes used in the heat ﬂow measurements penetrate
(Mehrikov etal., 1976). It should be noted that the actual boundaries of the elevated heat

flow region are difﬁcult to constrain with the available data.

Conclusions
The method of Ruff et al. (1994) allows one to obtain corrections in origin time
and timing errors and allows rapid identiﬁcation of spurious arrivals reported in the
Russian bulletins. Combined with relocations of epicenters, this method has allowed the
reﬁning of the ﬁrst-order crustal structure of northeast Russia using available phase data
and the investigation of crustal thickness and upper mantle velocities at individual

stations. This work conﬁrms that a simple crustal model is a superior method of locating

86

earthquakes in the region; new earthquake relocations show the original Russian locations
contain systematic errors resulting from the use of a travel time curve with excessive
velocities. This study has resolved a slightly thinner crust in portions of the Chersky
Seismic Belt, which likely reﬂect the extensional episode associated with the Moma rift
and present Laptev Sea rift systems. This study has also demonstrated the applicability
of the ’SQUINT’ program to a geographically large area with sparse station coverage.
For future works, data from the Yakut network for Magadan region events (and vice
versa) will improve the existing data set, and allow determinations of crustal thickness
at additional stations, particularly in the northern Sakha Republic (Y akutia) and Chukotka.
I also plan to combine data from Alaska and Magadan to study the Bering strait region
and to research the possible existence of a Bering Sea block. The extension of this study
will also provide additional constraints on the tectonics and evolution of this highly

complex region.

APPENDICES

87

APPENDIX A

Earthquake data for events shown in Figure 7 and Figure 11. Events preceded by
an asterisk were used in the determination of crustal structure. Bulletin data is from
Materialy Po Seismichnosti Sibiri, except as noted. All events were relocated using only
Pg arrivals and using only ﬁrst arrivals (primarily Pn). Epicenters and new origin times
were determined with high residual stations removed. Dashed lines indicate where
insufﬁcient data were available for relocation, or where the relocation was unstable.

88

APPENDD( A

 

 

DATE BULLETIN LOCATION PG REUDCATION 1s: ARRIVAL RELOCATION
ORIGIN TIME EPICENTER ORIGIN TIME EPICENTER ORIGIN TIME EPICENTER N0-
YR MO or HR MN sa.c LAT LONG HR MN sa.c LAT LONG HR MN SE.C LAT LONG TES
76—01-21 06 01 55.0 67.8 140.20 06 01 55.4 66.661 138.390 06 01 47.2 67 765 140 276
76-02-07 22 58 01. 72.2 132.40 --------------------------------------------------
76-02-11 04 oo 59. 72.1 131.20 --------------------------------------------------
76-04-08 04 21 00. 67.1 139 70 --------------------------------------------------
76-04-18 07 38 07. 60.8 154.40 07 38 04.8 60.662 154 570 -------------------------
76-04-26 20 12 19. 61.7 156.30 20 12 19.0 61.657 156 206 -------------------------
76-05-08 11 39 26.6 60.06 152.74 11 39 25.5 60.088 152 726 11 39 25.7 60.006 157.787
76-06-24 09 52 20. 60.2 157.20 --------------------------------------------------
76-06-24 17 58 05. 59.8 157.40 17 57 52 5 59.532 158 879 -------------------------
76-07-01 13 42 05. 72.0 133.70 --------------------------------------------------
76-07-04 23 23 35. 65.7 135.00 --------------------------------------------------
76-07-16 07 53 42. 69.6 138.60 --------------------------------------------------
76-07-24 18 47 42. 72.2 137.80 --------------------------------------------------
76-08-03 16 21 31. 60.4 147 00 16 21 28 0 60.218 146 876 -------------------------
76-08-22 20 02 33. 72.8 125.00 --------------------------------------------------
76-08-22 20 03 52. 72.8 125.00 --------------------------------------------------
76-08-22 23 43 40. 74.3 141.20 --------------------------------------------------
76-08-26 22 49 50. 72.6 129.00 --------------------------------------------------
76-08-29 01 39 49 60.9 132.60 --------------------------------------------------
76-09-07 20 04 31. 61.3 156.00 20 04 22 5 61.048 156 803 -------------------------
76-09-29 06 05 50. 61.9 147.00 06 05 46 7 61 744 146 857 -------------------------
76-09-30 21 05 39. 58.0 147.10 --------------------------------------------------
76-10-03 23 16 08. 63.1 150.70 --------------------------------------------------
77-01-11 09 02 21 66.5 141.50 --------------------------------------------------
77-01-24 15 19 57.2 59.04 149.44 --------------------------------------------------
77-02-03 11 13 27. 61.3 156.70 11 13 33 0 61.704 155 894 -------------------------
77-02-15 06 58 10. 62.5 147.00 --------------------------------------------------
77-02-15 23 35 38. 75.1 124.80 --------------------------------------------------
77-02-26 04 39 10. 64.0 157.60 --------------------------------------------------
77-03-09 05 34 37. 60.0 152.80 --------------------------------------------------
77-03-18 09 54 56.8 60.50 148.08 --------------------------------------------------
77-04-10 15 48 41. 66.1 142.20 --------------------------------------------------
77-04-13 02 01 10. 58.2 133.90 --------------------------------------------------
77-05-03 11 4o 24. 60.6 161.60 ------- ------------------ 11 40 29 2 60.806 160 569
77-05-13 10 52 38. 59.0 150.70 --------------------------------------------------
77-05-14 21 18 58. 59.0 150.80 21 18 58 59.022 150 668 21 18 56 8 58.960 150 367
77-06-21 06 05 38. 61.7 139.20 --------------------------------------------------
77-06-27 17 47 19.8 63.00 146.41 17 47 15 9 62 774 146 185 17 47 16 1 62.809 146 287
77-09-12 03 39 00. 62.9 155.10 03 39 04 0 62.878 154 338 -------------------------
77-09-19 07 37 24. 73.2 124.80 --------------------------------------------------
77-10-13 01 57 56. 60.6 153.40 --------------------------------------------------
77-10-29 01 31 07. 67.8 142.00 --------------------------------------------------
77-11-06 04 31 23. 59.4 146.50 04 31 15.6 59 066 146 130 -------------------------
77-11-06 07 41 03. 61.4 144.70 07 41 01.0 61.318 144 556 -------------------------
77-11-18 21 55 42. 60.2 143.40 21 55 35.7 60.125 143 317 21 55 3 1 60 3 143 500
77-11-18 21 55 39.4 60.05 143.32 21 55 35.7 60.125 143 317 21 55 3* 6 60 0’" 143 179 isc
77-11-27 10 17 03. 62.4 153.00 10 17 00.9 2.418 152 909 -------------------------
77-12-06 20 54 22. 61.4 147.00 20 54 20.0 61 897 147 046 -------------------------
77-12-29 18 24 19.2 64.14 145.00 --------------------------------------------------
78-01-03 03 17 36. 68.0 139.70 --------------------------------------------------
78-02-05 21 08 05. 71.0 131.70 --------------------------------------------------
78-02-08 23 38 45. 67.78 132.65 --------------------------------------------------
78-02-22 23 41 48. 63.3 146.30 23 41 4 8 63.046 145 992 -------------------------
78-03-20 18 34 36. 64.8 148.00 18 34 32 3 64.769 148 030 -------------------------
78-03-28 18 57 23. 58.9 151.20 ------------------------- 18 57 06 8 58.836 151 126
78-05-04 19 46 13. 61.3 122.60 19 46 09 0 61.263 122 677 -------------------------
78-05-05 16 06 58. 67.8 139.50 --------------------------------------------------
78-05-26 14 28 12. 71.7 145.20 --------------------------------------------------
78-06-05 07 05 55. 60.2 160.10 ------------------------- 07 05 46 7 59 824 161 569
78-06-05 21 01 39. 60.0 159.70 ------------------------- 21 01 41 0 60 279 159 471
78-06-05 21 01 37. 60.16 160.39 ------------------------- 21 01 35 2 60 213 160 390 isc
78-06-22 06 12 38. 63.1 145.50 06 12 35 2 2.925 145 226 -------------------------
78-07-17 11 04 04. 60.6 158.00 11 03 34 7 59.806 160 660 -------------------------
78-08-22 17 41 40. 61.3 144.60 17 41 37 7 61.203 144 390 17 41 39 5 61 289 144 417
78-08-22 18 26 31. 61.2 159.80 --------------------------------------------------
78-09-01 00 22 11. 66.1 42.60 --------------------------------------------------
78-09-03 22 42 26. 70.2 141.20 --------------------------------------------------
78-10-12 03 55 38. 72.4 138.40 --------------------------------------------------
78-10-15 17 16 31. 63.8 154.00 17 16 1.7 64.881 154 895 17 16 27.4 63.958 154 184
78-10~27 06 34 42. 64.6 145.10 06 34 39.5 64.617 145 312 06 34 40.3 64.778 145 217
78-10-28 09 21 20. 64.4 145.20 09 21 18.1 64 526 145 112 09 21 19.1 64.596 145 065
78-10-28 09 21 20. 64.72 145.05 09 21 18.1 64.526 145 112 09 21 19.9 64.633 145 031 15C
78-11-13 13 29 13.3 59.59 149.18 13 29 14.5 59.584 149 500 -------------------------
78-12-02 15 37 03. 73.2 139.80 --------------------------------------------------
78-12-05 11 19 09. 67.4 126.10 --------------------------------------------------
78-12—06 08 20 48. 63.6 144.20 08 20 44 5 64.175 145 575 -------------------------
79-04-10 02 12 19. 69.7 138.00 --------------------------------------------------

 

79—04—28
79-05-02
79-05—15
79—06~05
79-06-05
79-06-16
79-06-23
79—06-27
79-07-13
79-08-18
79-08-19
79-08-27
79-09-10
79-10-03
79-10-07
79-10-09
79-10-26
79-10-30
79-11-03
79—11-11
79-11-18
79-12-09
79-12-21
79-12-25
79-12-29
80-01-10
80-01-18
80-01-25
80—01927
80-01-28
80-02-01
80—02-01
80-02-01
80-02-01
80-02-02
80-02-02
80-02-02
80—02-03
80—02-03
80-02-03
80~02-05
80-02-10
80-02-12
80-02-14
80-02—17
80-03-11
80-03-12
80-03—17
80-03-20
80-04-03
80-04-22
80-05—07
80-05-12
80-05-12
80-05-19
80-06—02
80-06—07
80-06-22
80-07~O9
80-07-14
80-09-19
80-09-24
80—09-26
80-10-16
80-11—08
80-12-03
80-12—17
80-12-27
80-12-29
80-12-31
'81-02-02
81-02-05
81-02-22
81-03-01
81-03-15
'81-05-10
81-05-22
81-05-22
81-05-27
81-06-19
81-07-03
81-07-16
81-07-27
81-08-03
81-08—09
81-08-19

000

I I I I O I I I I O I O I I I I I I I C I I I I I I I I I I I I O I I I I I I I I I I C I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I
whd¢moddNOO‘WﬁNQﬁOU‘D-‘QU‘OGDU‘UWWWOUQOHHULﬂU‘O‘QNHquWONNNHHHNNNWU‘ﬁOUOLﬂNWNNWU‘GWQQQO‘OO‘O‘DWNQthHN

W

DJ

0000

152.
149.
145.
117.
117.
143.
133.
137.
130.
131.
158.
145.
153.
144.
144.
144.
153.
131.
124.
153.
153.
153.
132.
154.
142.
148.
124.
145.
150.
150.
122.
122.
122.
123.
122.
122.
122.
122.
122.
122.
146.
124.
123.
124.
135.
127.

17')

129.
125.
117.
136.
152.
147.
147.
144.
145.
145.
146.
122.
131.
148.
125.
132.
129.
125.
152.
130.
143.
138.
140.
144.
132.
151.
143.
138.
157.
156.
156.
139.
151.
137.
144.
144.
132.
146.
140.

89

Appendix A

--——--—---

_-__-.._-..o

..........
__________
----------
——————————
..........
..........
..........
..........
——————————
——————————
..........
----------
——————————

-—-————-——

_------—--
--_-————--

(continued)
59.476 151.609
64.201 149 217
63.365 145 131
64.910 143 671
58.111 133 677
60.242 131 734
60.941 164 754
2.690 146 643
60.466 153 153
65.064 144 072
65.015 144 059
2.190 153 841
62.282 153 821
62.240 153 802
62.254 153 416
60.267 154 318
61.374 142 694
64.880 149 777
64.307 145 250
63.395 150 571
63 506 150 656
57.010 127 670
60.332 151 944
63.146 147 648
63.147 147 667
62.828 145 765
64.066 145 100
59.624 146 011
63.250 148 172
63.809 152 133
69.754 139 814
62.385 144 471
58.139 134 501
63.176 150 968
62.216 143 226
61.477 157 22
61.045 156 728
61.045 156 72
63.775 151 695
61.931 145 968
60.968 143 614
70.209 129 172
63.416 146 506

--——-——-——

--——------

___..-__—__

__-—--—-_.—

--_-..__-——

_—————---.-

_---__--__

-__.-_-_-_-

—-—---—--—

___-—————-

--__--_——---—--

58 625 133 452
6C.786 166 109
65 065 144 078
62.326 153 945
62 226 153 843
62 259 153 814
62 281 153 298
61.742 143 264
63 443 150 502
63.465 150 676
73 226 119 769
56.959 127 694
60.301 151 961
62 997 147 439
63 386 148 069
62 973 146 034
64 244 145 148
59.987 146 367
63.125 148 160
63 674 152 402
69.663 138 490
64 151 140 975
62 342 144 434
63 111 150 973
61 943 142 760
61.586 157 228
61.361 156 543
63.326 146 245

k,l

isc

81-08-26
81-08-29
81-08-29
81-10—20
81-10-20
81-11-03
'81-11-08
81-11-08
81-11-08
81-11-09
81-11-10
81'11—10
'81-11-10
'81-11-11
81-11-11
81-11-28
81-12-03
'81-12-08
82-03-12
82-04-05
'82-04-06
82-06-23
82-07—24
'82-08-04
82-09-03
82-09-08
82-09-09
82-09-19
82-09-22
82-10-04
82-12-22
'82-12-22
82-12-29
83-01—04
83-03—04
'83-03—12
83503-12
83-03-23
'83'03—25
83-03—25
83-04-04
‘83—05-09
83-05—10
83-05-28
83-05-28
83-06-08
83—06-10
83-06—10
83-06-26
83-10~12
83-10-12
'83~10-25
83-11-07
84-04-01
84-04-11
84-07-14
84-07-19
84-08-02
84-08-02
84—08-08
84-08-12
84—08512
84-08-12
84-08-12
'84-08-21
84-09-03
84-09-12
84-09-19
84-10-29
84-11—21
84-11-22
84-11-27
’84-12-02
'84—12-02
85-01-13
85-01-15
85-01-16
'85-01-21
'85-01-24
85-01-29
'85-01-29
85-01-29
85-02-01
85-02-01
85-02-01
85-02-01

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153.
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129.
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152.
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138.
141.
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122.
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163.
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140.
150.
150.
153.
141.
123.
155.
133.
145.
145.
145.
127.
127.
127.
145.

90

Appendix A

-—---—---_

-——-———-——

--—_--_---

-____-_—-—

__-_-_---_

(continued)
58.338 141 057
65 356 136 736
65 356 136 736
61.822 153 724
61.822 153 724
61 801 153 687
61.840 153 722
64.327 148 978
64 327 148 978
63 914 148 675
1 856 153 674
61 767 153 72
62 201 154 270
63 871 148 372
61 798 153 662
59 401 148 058
61.791 153 669
60.275 138 221
63.563 146 219
62 370 146 957
66 989 133 414
62.562 151 037
59.425 152 022
59.684 141 313
63.885 156 648
59.201 152 693
62 155 143 655
64.275 140 871
64.216 141 027
63.046 155 746
63 560 149 797
63.560 149 797
66.942 140 073
63 287 146 227
64.193 150 838
61.991 150 358
59.465 148 088
75.035 134 995
75.035 134 995
60.026 149 772
60.001 149 904
60.034 153 031
65 537 136 343
59 142 146 190
59.419 148 080
60 6 - 145 244
60 6 2 145 244
60 893 153 842
61 145 136 623
63.393 145 635
61 876 163 794
61 230 156 433
68 320 141 169
63.376 150 560
63.321 150 579
60 02 153 184
65 007 141 723
60 782 155 319
66 900 132 840
64.116 145 801
64.116 145 801
64 200 145 878
62 855 127 144
62 855 127 144

_-_—-_-------——

----——----

o---~-—-__

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65.389 136 315
65.374 136 469
61.885 153 616
61.857 153 615
61.918 153 737
64.018 148 711
63 983 148 703
63.901 148 588
61.918 153 629
63.867 148 820
61.833 153 548
61.807 153 631
61.818 153 515
60 252 138 615
63.563 146.537
62 413 147. 27
66 883 132 813
64.135 156 929
59.195 152 658
62.250 143 772
64.342 140 893
63.046 156 214
63 609 149 807
63.543 149 933
67.005 140 107
63 377 145 777
61.006 150 352
59.527 148 188
73.439 122 138
73.429 128 102
59.965 150 048
60 145 152 850

5 385 136 508
59.490 148 123
61 750 143 902
60.843 144 703
74.094 134 579
60.983 153 770
61.162 136 660
63.393 145 750
62 408 163 551
68.492 140 875
63.418 150 534
63.339 150 366
59.997 153 156
60 759 155 302
66 871 132 799
64 205 145 852

----————-——----_

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15C

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81-08-26
81—08-29
81—08—29
81—10-20
81-10-20
81-11-03
*81-11-08
81-11-08
81-11-08
81-11—09
81-11-10
81-11-10
1'81-11--10
*81-11-11
81-11-11
81-11~28
81-12-03
'81-12-08
82-03-12
82-04-05
'82-04-06
82-06-23
82—07-24
'82-08-04
82-09-03
82-09—08
82-09-09
82-09-19
82-09—22
82-10—04
82-12-22
'82-12-22
82-12-29
83-01-04
83-03-04
‘83-03—12
83-03-12
83-03-23
‘83-03-25
83-03-25
83—04-04
'83-05—09
83-05-10
83-05—28
83—05-28
83-06-08
83-06-10
83-06—10
83-06-26
83-10-12
83-10-12
*83-10—25
83-11-07
84-04-01
84-04-11
84-07-14
84-07-19
84-08-02
84-08-02
84-08-08
84-08-12
84-08-12
84-08-12
84-08-12
‘84-08-21
84-09-03
84-09-12
84-09-19
84-10-29
84-11-21
84-11-22
84-11-27
‘84-12-02
‘84-12—02
85-01-13
85-01-15
85-01-16
*85-01-21
'85-01-24
85-01-29
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148.
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153.
153.
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146.
133.
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151.
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152.
140.
143.
138.
141.
140.
155.
149.
149.
140.
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150.
134.
150.
148.
122.
122.
130.
150.
150.
153.
136.
146.
148.
136.
132.
144.
144.
152.
136.
135.
137.
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163.
156.
140.
140.
150.
150.
153.
141.

12

155.
133.
145.
145.
145.
127.
127.
127.
145.

Appendix A

_-——-—--—-

——--——--—-

_--——--——-

---—--——--

~.-——-—.———

90

(continued)
58 338 141 057
65.356 136 736
65.356 136 736
61.822 153 724
61.822 153 72
61.801 153 687
61.840 153 722
64 327 148 978
64.327 148 978
63.914 148 675
61 856 153 674
61.767 153 724
62.201 154 270
63 871 148 372
61.798 153 662
59.401 148 058
61.791 153 669
60.275 138 221
63.563 146 219
62.370 146 957
66 989 133 414
62.562 151 037
59.425 152 022
59.684 141 313
63.885 156 648
59.201 152 693
62 155 143 655
64.275 140 871
64.216 141 027
63.046 155 746
63 560 149 797
63.560 149 797
66.942 140 073
63.282 146 22
64.193 150 838
61.991 150 358
59.465 148 088
75.035 134 995
75.035 134 995
60.026 149 772
60.001 149 904
60.034 153 031
65 537 136 343
59.142 146 190
59.419 148 080
60.612 145 244
60.612 145 244
60.893 153 842
61 145 136 623
63.393 145 635
61 876 163 794
61.230 156 433
68.320 141 169
63.376 150 560
63.321 150 579
60.025 153 184
65 007 141 723
60 782 155 319
66.900 132 840
64.116 145 801
64.116 145 801
64 200 145 878
2.855 127 144
62.855 127 144

----------

--—----_--

-_—-__——--

..----____-

65.389 136 315
65.374 136 469
61 885 153 616
61.857 153 615
61.918 153 737
64 18 148.711
63 983 148 703
63 901 148 588
1 918 153 629
63.867 148 820
61.833 153 548
61.807 153 631
61.818 153 515
60 252 138 615
63 563 146 537
62 413 147.027
66 883 132 813
64 135 156 929
59 195 152 658
62.250 143 772
64.342 140 893
63 046 156 214
63 609 149 807
63 543 149 933
67 005 140 107
63 377 145 777
61 006 150 352
59 527 148 188
73 439 122 138
73 429 128 102
59.965 150 048
60 145 152 850
5 385 136 508
59.490 148 123
61 750 143 902
60 843 144 703
74.094 134 579
60 983 153 770
61 162 136 660
63 393 145 750
62 408 163 551
68.492 140 875
63.418 150 534
63.339 150 366
59.997 153 156
60.759 155 302
66 871 132 799
64.205 145 852
64.242 145 85
63 011 127 452
63 016 127 540

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15:

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35-02-02
85-02-18
'85-03-08
85—04-10
35-04-12
85—04-17
85-04-20
85—05-22
85-06-02
‘85—06-02
85-06—24
85-06-24
85-08-20
85—08—28
85-09-10
85-10-05
85—10-05
85—10—05
'85-11—28
86-01-05
'86—01-18
86-01-24
86-01-25
'86-02-15
'86—03-07
86-03-15
86—04-03
'86-04-06
86-04-23
86—05—11
86—06-04
86-06-15
86-06-15
86-06-15
86-07-23
86-07-27
86-07-27
86-08-10
86-11-09
86-12—05
86-12-08
86-12-11
86-12-11
86-12-18
'86-12-18
86-12—22
'86—12—26
87—01—09
87-01—09
87—01—16
87-01-19
87—02-11
'87-02-11
'37-02-11
'87-02-11
'87-02—11
87-02-11
87-02-11
'87-02—11
87—02-11
*87-02-11
'87-03-04
87-03-08
87-03—16
'37-04—13
87-04—15
87-04-22
87-07-03
87-07-05
87-07-17
87-07—21
'87-09-09
87-09—27
87-10—06
87-10—08
87—11-25
87-11-26
87-11-29
87-12-07
87—12-30
88-01-01
88—01-01
88—01-13
88—01-19
88-01-30
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150.
150.
144.
128.
153.
138.
147.
152.
153.
144.
154.
130.
114.
154.
158.
126.
126.
126.
128.
147.
160.
147.
139.
125.
140.
119.
119.
143.
143.
119.
149.
153.
140.
125.
116.
156.
156.
156.
156.
156.
156.
156.
156.
156.
156.
148.
143.
167.
143.
121.
129.
148.
144.
118.
149.
150.
160.
119.
119.
118.
119.
119.

118.
130.
130.
129.
145.
117.
148.

Appendix A

11 28 44.

--_--_----

_-—————.—--

——_--—————
-___-————-
—-_--_-.-_-
---_---_--
--——--—--—

-n--—--—--

_-.—--w----

-----__---

91

(continued)
65.834 136.990
65.557 136.457
59.356 152 162
70 329 141 424
65.406 142 946
60 952 157 850
64.857 144 044
64 857 144 044
5.286 144 664
65.286 144 664
62.237 145 488
59.956 137 081
59 465 150 201
59.299 149 987
59 225 150 192
64.863 144 133
70.276 128 612
60.191 153 761
60 616 138 566
63 973 153 096
64 104 153 511
59 135 154 478
70 755 130 200
62.034 154 151
61.871 159 02
72 883 126 515
72.883 126 515
64.634 147 058
63.532 147 931
61 177 143 634
61 177 143 634
61 375 149 426
59.974 153 039
7.162 140 135
58 644 125 067
62 868 156 909
62 868 156 909
62 840 156 867
2 859 156 804
62 812 156 721
62.851 156 849
62.656 156 060
62.846 156 811
61 116 148 472
64 106 167 266
66.207 143 085
58 633 121 561
72.211 29 863
59.394 148 709
61.316 144 483
73.653 118 581
58.942 149 728
60.149 150 386
61 061 161 183
73 202 121 342
72.907 121 943
63 795 145 669
74 405 131 060
74.405 131 060
71 451 128 982
63 663 145 512
64.318 148 521

—-______-—

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662 136 653
5° 119 152 197
.87. 144 60
6‘ 89 144 749
65.205 144 346
59.430 150 179
64 850 144 422
60.255 153 530
64.001 15 038
64 106 153.469
58.975 154 750
70 748 130 241
6: 157 154.243
72 946 125.867
72 63 173.975
64.569 147 062
63.500 147 731
60.361 145 102
61 135 143 533
61 403 149 465
59 262 154 51
58 618 124 947
2 826 156 871
62 860 156 856
6; 836 156 850
2 741 156 777
62 809 156 347
62 823 156 856
62 595 155 096
62 825 156 814
61 128 148 374
64.204 167 313
58 67 121 649
72.195 129 668
59 401 148 827
61 680 144 692
73 706 118 087
56 749 149 651
60 121 150 54
61 039 161.273
73 693 119 566
73 763 119 695
73 788 118 661
73.730 119 238
63 716 14 630
74.682 130 977
74 584 130 687
71 449 129 227
64.335 148.554

isc

isc

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'1'!)

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85-02-02
85-02-18
'85-03-08
85-04-10
85-04-12
85-04-17
85-04-20
85-05-22
85-06-02
'85-06-02
85-06-24
85-06-24
85-08-20
85—08-28
5-09-10
85-10-05
85-10-05
85-10-05
’85—11-28
86-01-05
'86—01—18
86-01-24
86—01—25
'86-02—15
'86—03-07
86-03-15
86—04—03
‘86-04«06
86-04—23
86-05-11
86-06‘04
86-06-15
86-06-15
86-06-15
86-07-23
86-07-27
86—07-27
86-08—10
86-11-09
86-12—05
86-12—08
86-12-11
86—12-11
86-12—18
'86—12-18
86-12-22
'86-12~26
87-01-09
87-01—09
87-01-16
87-01-19
87-02—11
'87-02-11
'87-02-11
'87-02-11
'87-02-11
87—02—11
87-02-11
'87—02-11
87-02-11
'87—02-11
'87—03-04
87-03-08
87-03-16
'87-04-13
87-04-15
87—04-22
87-07—03
87-07-05
87—07-17
87—07-21
‘87—09-09
87-09-27
7-10—06
87—10-08
87-11-25
87-11—26
87-11-29
7-12-07
87-12—30
88-01-01
88—01—01
88-01-13
88-01-19
88-01-30
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144.
144.
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142.
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150.
150.
144.
128.
153.
138.
147.
152.
153.
144.
154.
130.
114.
154.
158.
126.
126.
126.
128.
147.
160.
147.
139.
125.
140.
119.
119.
143.
143.
119.
149.
153.
140.
125.
116.
156.
156.
156.
156.
156.
156.
156.
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156.
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148.
143.
167.
143.
121.
129.
148.
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118.
149.
150.
160.
119.
119.
118.
119.
119.
145.
118.
130.
130.
129.
145.
117.
148.

91

Appendix A

11 28 44.

—-——----—-

(continued)
65.834 136.990
65.557 136.457
59.356 152 162
70.329 141 24
65.406 142 946
60 952 157 850
64 857 144 044
64 857 144 044
65 286 144 664
5 286 144 664
62 237 145 488
59 956 137 081
59.465 150 201
59.299 149 987
59.225 150 192
64.863 144 133
70.276 128 612
60.191 153 761
60 616 138 566
63 973 153 096
64 104 153 511
59.135 154 478
70.755 130 200
62.034 154 151
61 871 159 025
72.883 126 515
2.883 126 515
64.634 147 058
63.532 147 931
61 177 143 634
61 177 143 634
61.375 149 426
59 974 153 039
67.162 140 135
58 644 125 067
62.868 156 909
62.868 156 909
62.840 156 867
62 859 156 804
62.812 156 721
62.851 156 849
62.656 156 060
62 846 156 811
61 116 148 472
64.106 167 266
66.207 143 085
58 633 121 561
72.211 129 863
59.394 148 709
1 316 144 483
73.653 118 581
58.942 149 728
60.149 150 386
61.061 161 183
73.202 121 342
72 907 121 943
63.795 145 669
74.405 131 060
74.405 131 060
71.451 128 982
63 663 145 512
64.318 148.521

----_-__--

-_---_--__

_--_-_—---

-—-—--__--

65. 2 13 653
59 1 37 197
64 871 144 060
64 8 8 144 249
65 205 144 346
59.43C 150 179
64 850 144 422
60.255 153 530
64.001 153 038
64.106 153 469
58.975 154 750
70.748 130 241
62.157 154.243
7 946 125 867
72 63C 1 3 97b
64 569 147 062
63.500 147 731
60.361 145.102
61 135 143.533
61 403 465
59 262 1‘4 152
58.618 124.947
62.82 156 871
62.860 156 856
62.836 156 850
62.741 156 777
62.809 156 847
62 823 156 856
62.595 155 096
62 825 156 814
61 12 148 374
64.204 167 313
58 670 121 649
72 195 129 668
59.401 148 827
61 680 144 692
73.706 118 087
56 749 149 651
60.121 150.454
61 039 161 273
73.693 118 566
73 763 119 695
73 788 118 661
73.730 119.238
63 716 145 63

74 682 130 977
74.584 130 687
71.449 129 227
64 335 148 554

isc

isc

isc

85—02-02
85-02—18
'85—03-08
85-04-10
85—04-12
85—04-17
85-04-20
85-05-22
85-06-02
'85-06-02
85—06—24
85-06—24
85-08-20
85-08-28
85-09-10
85-10-05
85-10-05
85-10-05
'85-11-28
86-01-05
'86—01-18
86-01-24
86-01-25
'86-02—15
'86—03-07
86-03-15
86-04-03
'86-04—06
86—04—23
86-05-11
86-06-04
86-06—15
86-06-15
86-06-15
86-07-23
86-07-27
86-07-27
86—08-10
86—11-09
86-12-05
86-12-08
86-12~11
86-12«11
86-12-18
'86-12-18
86-12—22
'86-12—26
87-01-09
87-01-09
87-01-16
87-01-19
87—02-11
'87-02-11
'87—02-11
'87-02-11
'87—02-11
87-02-11
87-02-11
*87—02—11
87-02-11
*87-02-11
'87-03-04
87-03-08
87-03-16
'87—04-13
87-04-15
87—04-22
87-07-03
87-07-05
87-07—17
87-07-21
’87-09~09
87-09-27
87-10-06
87—10-08
87-11-25
87-11—26
87-11—29
87-12507
87-12-30
88-01-01
88-01-01
88-01-13
88-01-19
88-01-30
’88—02-19

aswoowuqn oomo‘moo

OU‘QCDU

OO‘O‘DhNN COG) meDNr-l

‘OH‘JW bNQWU‘ﬁU‘D-Hxl

coma)

(7‘0

on

03in

(DC

on

150.
150.
144.
128.
153.
138.
147.
152.
153.
144.
154.
130.
114.
154.
158.
126.
126.
126.
128.
147.
160.
147.
139.
125.
140.
119.
119.
143.
143.
119.
149.
153.
140.
125.
116.
156.
156.
156.
156.
156.
156.
156.
156.
156.
156.
148.
143.
167.
143.
121.
129.
148.
144.
118.
149.
150.
160.
119.
119.
118.
119.
119.
145.
118.
130.
130.
129.
145.
117.
148.

Appendix A

11 28 44.

--—--—----

91

(continued)
65.834 136.990
65.557 136.457
59.356 152.162
70.329 141 42
65.406 142 946
60 952 157 850
64 857 144 044
64 857 144 044
65 286 144 664
65 286 144 664
62 237 145 488
59 956 137 081
59.465 150 201
59.299 149 987
59.225 150 192
64.863 144 133
70.276 128 612
60.191 153 761
60 616 138 566
63.973 153 096
64.104 153 511
59.135 154 478
70.755 130 200
62.034 154 151
61.871 159 025
72.883 126 515
2.883 126 515
64.634 147 058
63.532 147 931
61 177 143 634
61 177 143 634
61.375 149 426
59.974 15 .039
67.162 140 135
58 644 125 067
62.868 156 909
67.868 156 909
62 840 156 867
62.859 156 804
62.812 156 721
62.851 156 849
62.656 156 060
62.846 156 811
61.116 148 472
64.106 167 266
66 207 143 085
58.633 121 561
72.211 129 863
59.394 148 709
61.316 144 483
73.653 118 581
58.942 149 728
60.149 150 386
61.061 161 183
73.202 121 342
72.907 121 943
63.795 145 669
74 405 131 060
74.405 131 060
71.451 128.982
63 663 145 512
64.318 148 521

--...o--—---

—-..—_—----

—-__--—-—-

-..--..—-——-

——--~—...—.

65 62 136 653
‘9 ‘19 152 197
64.87 14 060
64.898 144 249
65 205 144 346
59.430 150 179
64 850 144 422
60 255 153 530
64 001 15 038
64 106 153 469
58 975 154 750
70.748 130 241
62 157 154 243
7- 946 125.867
72 63 123 975
64 569 147 062
63.500 147 731
60.361 145 102
61 135 143 533
61.403 149 465
59 262 154 152
56.618 124 947
6‘ 826 156 871
67 860 156 856
2 836 156 85
62 74 156 777
6; 809 156 847
62 823 156 856
62 595 155 096
62 825 156 814
61 128 148 374
64.204 167 313
58 670 121 649
72 195 129 668
59 401 148 82
61 680 144 692
73.706 118 087
56 749 149 651
60 121 150 54
1 039 161 273
73 693 118 566
73 763 11 695
73 788 118 661
73 730 119 238
63 716 145 630
74.682 130 977
74.584 130 687
71.449 129 227
64 335 148 554

isc

isc

isc

‘88-02-19
'88-04-03
88-04-03
88-04-05
88-04-05
‘88-05-25
88-06-01
'88-06-09
'88-06-14
88-06-29
88-07—01
88-09—22
'88-10—17
88-10-25
88-12-24
88-12-30
89-01-05
89-01-14
89-01-15
'89-01-29
89-02-17
89-02-25
89-03—01
'89-03-21
89—04-09
‘89-04-09
89—04-24
89-05-19
89-05-24
'89—06-16
89-06-16
89-06-30
89-07-02
'89-07—07
'89-07-09
89-07—25
89-08-05
89-08-05
89-08-05
89-08-05
89-08-05
89-08-08
89-09-04
89-09-26
89-09-26
'89-10-04
89—11-13
89-12-14
89-12-18
89-12-22
90-03-02
90-03-06
90-03-13
90-03-13
90-03-14
90-03—21
‘90-03-29
90-04-02
90-04-11
90-05—05
'90-05-30
90-06-09
'90-06-25
90-06—28
90-06-28
90-07-06
90-07-11
‘90-07-12
90-07—24
*90—08-24
90-09-11
*90—11-01
90-11-02
'90-11-02
90-11-02
90-11-21
90-11-21
'90-11-22
90-12-08
‘90-12-13
‘91—02-10
91-02-11
91-03-01
’91-03-01

91-03-30

O‘tho ooooao

U‘LJOUQH

tho-I

ﬁkOWHU‘NﬁO‘GDWO

wwnwoo

\IOU‘NU‘ \OOOK

ubt-‘KOQWCD

O

HU‘H

0

CG)

NOervu—nmm
~.)

03

NNb-O
coco H

@mOm
up»:

bx.)
\OW

meoh
U‘NO‘OH

ON
a

145.
138.
138.
130.
129.
150.
161.
157.
149.
132.
145.
160.
148.
148.
149.
153.
140.
143.
151.
144.
129.
157.
117.
145.
145.
145.
151.
155.
144.
142.
145.
152.
150.
141.
152.
159.
133.
134.
131.
134.
130.
117.
148.
130.
134.
146.
143.
145.
141.
136.
115.
125.
133.
134.
133.
133.
145.
138.
154.
153.
144.
113.
130.
132.
134.
144.
125.
153.
142.
151.
116.
156.
156.
146.
146.
153.
142.
156.
152.
140.
145.
125.
126.
126.

126.

Appendix A

O

p—l

FJ

H

\O
HHouHo‘qubJRJKOV-‘CDO‘WU‘

H
\J
O
0‘
N
A
O

92

(continued)
64.171 145.827
69.428 138 694
69.502 138 654
64.209 150 934
63.266 157 627
63.356 149 579
64.880 145 689
61.934 160 047
62.824 148 904
62.891 148 867
64.006 148 913
61.118 153 705
72.824 141 324
61.946 143 800
57.964 150 965
62.825 144 936
69.830 129 137
61 715 157 701
64 920 145 199
59 774 145 194
59 774 145 194
58.904 151 856
62.411 155 229
61 217 144 460
63.564 142 778
61.020 145 457
59.350 152 686
59 578 150 119
64.991 141 596
59. 24 152 716
62.915 159 171
75.090 133 045
75.090 133 045
75.018 132 375
75.018 132 375
75.315 130 353
60.869 148 893
64.709 146 818
62.279 143 569
73.985 146 036
74.344 141 495
65.499 136 828
73.934 113 609
66.916 124 749
I3 173 134 461
73.173 134 461
73.356 134 217
73.071 133 596
64 010 145 044
61.969 137 944
61 964 154 280
61.321 153 95
62.915 144 806
66 827 130 342
75.300 132.311
75.299 132.311
67 194 144 699
62 057 153 827
60.332 142 664
63.032 151 219
74.465 115 860
61.309 156 763
61.244 157 005
64 733 146.620
64.733 146.620
59.929 153.414
61.836 142 953
62.767 156 743
59.429 152 484
64.433 140 518
2 950 145 634
72 577 125 222
77 173 126 820
72 173 126 820
66.845 126 251

———-_..__-—

_-_---_w—-

~—-q———--—

_---—--.-—-

64 187 14 853
69 477 138 476
76 567 127 948
64 161 151 000
63 30° 157 545
63 393 149 38
62 869 148 799
3 197 148 772
64.064 148 900
61 207 153 969
62 097 144 025
58 591 151 226
62.872 144 862
69 703 129 095
59 863 145 095
59 879 145 041
58 275 151 818
6“ 483 55 234
61 368 144 408
63 609 142 778
59.302 152 657
59.587 149 929
64 999 141 23
59 859 152 780
75 723 1 4 098
75 999 133 914
74 997 132 123
76 171 133 374
60.839 148 771
76 137 132 907
64 696 146 926
62 364 143 441
65.504 136 845
73 277 134 528
73.311 134 712
73 323 134 392
73.432 134 460
63 962 144 842
62 139 136 066
62 953 144 919
75 981 108 939
66.807 130 326
75 978 13 266
76 007 134 266
7.232 144 664
62 073 153 845
59 886 142 081
62 993 151 201
61.321 156 935
64 803 146 725
64 813 146 755
59.764 15' 604
62.773 156 835
64 501 140 457
6; 904 145 461
2 689 125 233
2 277 127 287
72 242 127 173

’ m,n

isc

isc

isc

isc

1 SC

i.isc

#199»va

(D‘s
000

93

Appendix A (continued)
91-04-01 07 21 57.9 71 38 130.00 07 21 57.2 71 401 130 094 ----------------------- 8
91-05-02 07 18 07.7 73 2 121.43 -------------------------------------------------- a
'91-07-02 13 43 48.7 65 18 139.84 13 43 45.0 65.174 139 816 ------------------------- a
91-07-24 02 26 04.7 62 23 143.68 ------------------------- 02 26 1.5 62 044 143 883 a
‘91-07—31 01 44 02.5 2.06 127.56 01 44 02.7 71 980 127.221 01 44 02.6 72 132 127 810 a
91-08—04 19 08 08.3 65 47 143.32 19 08 05.9 65 495 143 127 19 08 06.7 65 460 143 199 a
'91-08-04 19 08 07. 65.5 142.9 10 08 05.9 65 495 143 127 19 08 07.1 5 449 143 120 a.isc
'91—08—04 19 14 41.6 65.47 143.33 19 14 40.6 65 498 143 220 19 14 39.7 5 516 142 890 a
91-08-25 13 51 02.3 70.73 140.90 ------------------------------------------- a
'91-08-26 09 35 48.9 3.18 146.00 09 35 49.0 63 390 146 359 09 35 50. 63 464 146 522 a
91-10-13 00 36 37.3 61.09 144.93 00 36 33.4 61 112 144 907 00 36 26.5 60 746 145 318 a
91—10-28 21 41 31.4 65.18 131.64 -------------------------------------------------- a
91-12-23 06 04 17.9 62.41 140.89 06 04 16.0 62.454 140 848 06 04 17.0 62 854 140 570 a
'92-01—22 06 29 19.4 65.86 143.38 06 29 16.1 65 852 143 180 06 29 17.0 65 870 143 087 a
92-01-22 06 29 17.1 65.8 143.0 06 29 16.1 65 852 143 180 06 29 16.5 65 863 143 124 a.isc
92-01-28 00 07 28.5 68.16 133.12 00 07 29.6 68.302 133 967 00 07 23.6 68 211 132 319 a
'92-02-12 17 14 57. 64.8 152.90 17 14 51.2 64 972 153 224 17 14 52.1 64 908 153 172 a
92—02-15 04 52 10. 75.9 124.20 04 52 36.7 74.227 124 354 04 51 59.5 76 142 124 780 a
92-02-15 04 52 05.1 75.95 125.1 04 52 36.7 74 227 124 354 04 52 04.2 75 800 125 159 a,isc
92-02-22 17 55 21.4 70.14 139.38 17 55 20.9 70 091 139 399 17 55 21.7 70.133 139 589 a
92-02-23 08 21 42.3 70.06 139.45 08 21 41.2 70 031 139 378 08 21 41.4 70 065 139 498 a
92-05-07 23 22 56.5 63.63 133.53 ------------------------- 23 22 54.9 63 848 133 988 a
'92-06-28 23 53 20.6 63.79 145.10 53 17.4 63 704 145 682 23 53 18.1 63 739 145 720 a
92-08-26 11 02 17.4 71.76 133.14 ‘1 02 16. 71 572 133 208 11 02 17.8 71 832 133 410 a
92-09—09 00 14 37.3 71.26 132.07 -------------------------------------------------- a
92-09-13 21 43 00.4 62.00 154.13 ------------------------- 21 42 58.9 6' 110 153.715 a,isc
92-10-30 14 20 31.3 72.72 123.83 ------------------------- 14 20 30.2 7; 698 123.682 a
92-11-14 20 43 15.8 72.96 123.24 20 43 15.0 72 997 123 442 20 43 14.9 7' 976 123.300 a
'92-11-17 07 55 18. 67.2 128.80 07 55 13.8 67 258 128 590 O7 5 14.8 67 384 128.597 a
93—02-21 17 06 31.3 65.88 149.53 17 06 18.2 65.993 150 971 ------------------------- a
93-02-24 17 45 26.3 69.54 129.00 17 45 24.6 69.582 128 736 17 45 27.0 69.633 128 905 a
93-03-05 01 43 44.7 63.00 145.00 01 43 43.9 63.005 145 527 01 43 43.7 62.97, 145 679 a
*93-03-05 04 21 05.2 63.78 145.67 04 21 05.1 63.793 145 408 04 21 04.8 63.747 145 452 a
93-03-13 03 26 30.5 63.74 142.47 03 2 28.3 63 791 142 337 ------------------------- a
'93-03-22 18 14 05.9 62.91 145.67 18 14 06.8 63.041 145 315 18 14 07.4 63.087 145 327 a
‘93-03-24 16 19 08.5 65.34 142.69 16 18 05.9 65.341 142 609 16 19 06.5 65.492 142 633 a
93—03-24 22 43 32.4 71.58 129.76 22 43 30.3 71.541 130 109 22 43 28.5 7 .820 130 369 a
93-04-29 12 21 32.5 69.30 139.68 12 21 30.7 69.161 140 013 12 2 30.9 69 160 139 878 a
93-05-04 20 49 03.8 75.71 132.73 20 49 14.8 74.832 132 134 20 48 50.0 76 999 131 502 a
93-05—19 08 32 12.5 58.14 140.77 ------------------------- 08 32 15.3 58 313 139 867 a
93-06-15 11 51 15.4 62.23 141.70 11 51 12.9 62 287 141 543 11 51 14.9 62 290 141 492 a
93—06—18 19 16 17.6 2.08 146.30 19 16 14.4 62.051 146 166 19 16 14.2 62 109 146 255 a
'93—08-30 07 56 37.9 64.16 145.80 07 56 34.9 64.006 145 881 O7 56 34.5 64 020 145 905 a
93-09-26 10 58 27.7 59.81 144.95 -------------------------------------------------- a
93-10-02 04 04 06. 73.1 116.50 -------------------------------------------------- a
isc Earthquake parameters determined with supplemental information from Bulletin of the international

Seismological Center.

Bulletin origin time and epicenter also from BIS.

PN arrivals are misidentified in bulletin

a Phase data and parameters from B. Koz'min, Yakutsk Science lnstisute.
b For stations Omsukchan and Seimchan. PG arrivals are misidentified in Bulletin as PN arrivals.
c For stations Stekolnyi, Evensk, Ust' Nera, and Yakutsk.
as PG. Station Seimchan PG arrival misidentified in bulletin as PN.
d For station Omsukchan, PN arrival is misidentified in bulletin as PG.
e For station Seimchan. PN arrival is misidentified in bulletin as PG.
f For station Ust’ Nera, PN arrival is misidentified in bulletin as PG.
9 For station Stekolnyi, PG arrival is misidentified in bulletin as PN.
h For station Zyryanka, PG arrival is misidentified in bulletin as PN.
i Station Tenkeli is misidentified in Materialy as station Tungurcha.

identical appearing ruSSian codes.

j For
X For
1 For
m For
n For
0 For
p For
q For

For

'1

station Nezhdaninskoe.

station
station
station
station
station
station
station

station

Magadan.
Ust'
Moma.

Khandyga.

Yubileinaya.

Naiba,
Magadan.

Nel' Koba.

Omchug.

PN arrival is misidentified in

PN arrival is misidentified in

PN arrival is miSidentified in bulletin

bulletin

bulletin as

PG.

FC.

as

as PG.

PN arrival is misidentified in bulletin as PG.

PN arrival is misidentified in bulletin as PG.

PN arrival is misidentified in bulletin as PG.
PN arrival is misidentified in bulletin as PG.

PG arrival is misidentified in bulletin as PN.

PN arrival is misidentified in bulletin as PC.

This is likely due to nearly

S

t

94

Appendix A (continued)

Station Ust' Nera misidentified in Materialy as station Ust'Nyukzha.
identical appearing russian codes.

For station Omolon, PN arrival is misidentified in bulletin as PC.

This is likely due to nearly

95

APPENDIX B

Seismic station coordinates from the Yakut and Magadan networks. Stations
outside the study area but listed here were used in earthquake locations.

96
APPENDD( B

 

 

Station Name Code Elevation Latitude Longitude Region
(m) (N) (+E9'W)

Anadyr ANY 55 64.734 177.496 Magadan
Artyk AYK 700 64.181 145.133 Yakut
Batagai BTG 120 67.650 134.625 Yakut
Bilibino BIL 283 68.058 166.449 Magadan
Chagda CGD 180 58.750 130.617 Yakut
Cherskii CBS 40 68.750 161.333 Yakut
Chul’man CLN 600 56.867 124.900 Yakut
Debin DBI 332 62.339 150.750 Magadan
Dunai DUY 5 73.900 124.608 Yakut
Egvekinot EGV 18 66.323 - 179.127 Magadan
Evensk EVE 21 61.921 159.231 Magadan
Iul’tin ILT 245 67.875 — 178.733 Magadan
Khandyga KHG 125 62.650 135.557 Yakut
Khani KHN --- 57.017 121.000 Yakut
Khatystyr KHY 400 55.680 121.520 Yakut
Kulu KU- 655 61.892 147.427 Magadan
Kyusyur KYU 20 70.683 127.367 Yakut
Magadan MAG 78 59.560 150.803 Magadan
Maiskii MKI 261 68.975 173.700 Magadan
Markovo MKN 25 64.684 170.412 Magadan
Moma (Khonu) MKU 192 66.466 143.216 Yakut
Myakit MYA 660 61.417 152.083 Magadan
Naiba NAY 5 70.850 130.733 Yakut
Nelkoba NKB 531 61.336 148.808 Magadan
Neryungri NY G 700 56.675 124.650 Yakut
Nezhdaninskoe NZD 603 62.497 139.058 Yakut
Omolon 0M0 260 65.232 160.535 Magadan
Omsukchan OMS 527 62.515 155.774 Magadan
Provideniya PVD 25 64.427 - 173.225 Magadan
Saidy SAY 88 68.700 134.450 Yakut
Sasyr SSY 580 65.158 147.075 Yakut
Seimchan SEY 206 62.933 152.382 Magadan
Sinegor’e SNE 420 62.037 150.523 Magadan
Stekolnyi MGD 221 60.046 150.730 Magadan
Stolb SOT 50 72.400 126.825 Yakut
Susuman SUU 640 62.781 148. 149 Magadan
Tabalakh TBK 200 67.539 136.522 Yakut

Taimylyr
Takhtoyamsk
Talaya
Tenkeli
Tiksi

Tun gurcha
Ust’Nera
Ust’Nyukzha
Ust’Omchug
Ust’Urkima
Yakutsk
Zyryanka

TML

TLA
TLI

TUG
UNR
U82

U80
UUR
YAK
ZYR

Appendix B (Continued)

6O
1 1
730
1 10
30
300
485
400
550
600
94
120

97

72.610
60.202
61.129
70.183
71.632
57.317
64.569
56.561
61.133
55.300
62.015
65.717

121.917
154.678
152.392
140.783
128.872
121.500
143.228
121.592
149.631
123.267
129.678
149.817

Yakut
Magadan
Magadan
Yakut
Yakut

. Yakut

Yakut
Yakut
Magadan
Yakut
Yakut
Yakut

BIBLIOGRAPHY

98

BIBLIOGRAPHY

Andreev, T. A., 1984, Calculations using an ECM of parameters of weak earthquakes, in Shilo.
H. A., Vaschilov, Y. Y., Linkova, '1‘. 1., and Akhlamova, N. N., eds., Seismicheskie
Protsessi na Cevero-Vostoke SSSR: Magadan, SKVNII DVNTs AN SSSR, p. 116-127 (in
Russian).

Ansimov, E. M., Sedov, B. M., and Shvarts, 0.8., 1967, Seismic exploration in the Northeast
USSR, in Fotiadi, E. B., ed., Geologicheskie Rezul’taty Geoﬁzicheskikh Issledovanii v
Sibiri i na Del’nem Vostoke: Novosibirsk, Nauka, p. 438-442 (in Russian).

Avetisov, G. P., 1983, Seismologic data on‘the deep structure of the New Siberian islands and
adjacent sea areas: International Geology Review, v. 25, p. 651-660.

Avetisov, G. P., and Guseva, Y. B., 1991, Deep structure of the Lena Delta region according to
seismic data: Sovetskaya Geologiya, n. 4, p. 73-81 (in Russian).

Belyaevsky, N. A., 1974, The earth’s crust within the territory of the USSR: Moskva, Nedra, 278
p (in Russian).

Belyaevsky, N. A., and Borisov, A. A., 1974, Structure and thickness of the earth’s crust in the
USSR, in Nalivkin, D. V., ed., Struktura Fundamenta Platformennykh Oblastei SSSR:
Leningrad, Nauka, p. 381-393 (in Russian).

Bobrobnikov, V. A., and Izmailov, L. I., 1989, Present day structure and geodynamics of the
earth’s crust in the southeastem portion of the Yana-Kolyma system, in Lin’kova, T. 1.,
and Krasnyi,‘ L. L., eds., Geoﬁzicheskie Issledovaniya Pri Reshenii Geologicheskikh
Zadach: Magadan, SVKNII DVNTs AN SSSR, p. 5-23 (in Russian).

Bulin, N. K., 1989, Deep structure of the Verkhoyana-Chukotka folded region according to
seismic data: Ttkhookeanskaya Geologiya, v. 8(1), p. 77-85 (in Russian).

Cook, D. B., Fujita, K., and McMullen, C. A., 1986, Present-day plate interactions in northeast

Asia: North American, Eurasian, and Okhotsk plates: Journal of Geodynamics, v. 6., p.
33-51.

Crumley, S. G., and Parfenov, L. M., 1994, Preliminary Gravity Models Around the Kolyma
Structural Loop, Sakha Republic, Russia: Eos (T ransactions, AGU), v. 75(44) supplement,
p. 631.

99

Davydova, N. 1., Shvarts, Ya. B., and Yaroshevskaya, G. A., 1968, Wave patterns in deep
seismic sounding along Magadan-Kolyma proﬁle, in Deep Seismic Sounding of the
Earth’s Crust in the USSR: International Geology Review - Book Section, v. 10, p. 93-
102.

Drachev, S., 1994, Laptev Sea: The NAD drill sites: The Nansen Icebreaker, v. 6, spring, p. 1,7-
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