The Moma Range is a Late Cretaceous to Cenozoic, northeast verging fold-and-thrust belt situated along the western boundary of the North American plate in northeast Asia. The slow convergence between North America, Eurasia, and Okhotsk results in a zone of diffuse continental deformation. While the Moma Range is >150 km northeast of main plate boundary zone, the geomorphic character of major rivers along its northeast slope and the recent large-magnitude (up to 6.6 Mww) teleseismic earthquakes indicate that the Moma Range is actively undergoing crustal shortening and accommodating regional convergence.Changes in channel morphology, river knickpoints, and steepened channels suggest the existence of a break in uplift rates along a previously mapped thrust-sense shear zone. In the central portions of the fold-and-thrust, the deformation is focused along a structure ~30 km inboard of the deformation front. However, the large-magnitude earthquakes are focused in the western portions of the Moma Range, along thrust faults closer to outer edge of the fold-and-thrust belt. These contrasting styles of deformation along-strike are potentially linked to variations in decollement strength, syntectonic sedimentation, and the middle Cenozoic rifting event that shut down convergence in region. This brief rifting event may have caused significant thinning of the orogenic wedge of the fold-an-thrust belt by means of erosion and possibly crustal thinning. By the Pliocene, the North American--Eurasian rotation pole shifted north of The Moma Range, reestablishing convergence in the region, and resulting in the continued growth and internal deformation of the fold-and-thrust belt.
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