Characterization of a partitioned section of the Hoh Serh Fault: Mongolian Altai

Strike-slip faulting is often an integral component of strain accommodation in continental collisions. In the Himalayan orogenic belt, such faulting occurs up to 2000 km away from the area of primary deformation. This study characterizes the motion along two such faults, the dextral Hh Serh fault and a thrust splay, the Tsagaan Salaa fault, in the Mongolian Altai. Strike-slip motion is expressed in the field as drainage offset, topographic depressions, and tension gashes in Quarternary alluvium. Reverse motion is observed geomorphically as offset alluvial fans, strath terraces, and a rare geologic exposure of a gouge zone. Differential GPS profiles of one alluvial fan offset by the Tsagaan Salaa fault show 5.5 0.5 m of offset. Based on an estimated fan age of 7.5 2.5 ka, this value gives a shortening rate of 1.5 0.5 mm/yr across the Tsagaan Salaa Fault. Smaller offsets along the Tsagaan Salaa Fault on strath terraces suggest that the offset surveyed may record multiple ruptures