The<i>MS</i>= 7.3 1992 Suusamyr, Kyrgyzstan, earthquake in the tien shan: 2. Aftershock focal mechanisms and surface deformation

Abstract The MS = 7.3 Suusamyr earthquake of 19 August 1992 was a large, thrust-type earthquake in the northern Tien Shan of Kyrgyzstan, an intracontinental mountain belt in central Asia. Focal mechanisms of both the mainshock and 13 moderate-sized aftershocks are consistent with a seismotectonic setting that is dominated by NNW-SSE horizontal compression, which manifests itself in reverse faulting along roughly east-west trending, steeply dipping fault planes. The earthquake produced surface faulting at two widely separated locations, along two different fault segments, the total length of which was less than 4 km. Detailed measurements at one of the locations indicate a net slip of at least 4.2 ± 0.4 m. A wide variety of secondary surface effects was observed in the macroseismic zone that extended over an area of 2500 km2. The lack of extensive surface rupture from such a large event can be explained by a combination of (1) redistribution of the net slip at depth among the secondary splays that branches out from the main fault near the surface and (2) variable surface slip over the fault length. The active deformation associated with this event documents a structural style that involves steeply dipping, reverse faults extending from mid-crustal depths to the surface at nearly uniform dip, accommodating crustal shortening in the interior of the Tien Shan.