TheMS= 7.3 1992 Suusamyr, Kyrgyzstan, earthquake: 1. Constraints on fault geometry and source parameters based on aftershocks and body-wave modeling

Abstract We investigated the Suusamyr, Kyrgyzstan, earthquake of 19 August 1992, using aftershock data, teleseismic body-wave modeling, and field observations. Aftershocks were recorded by the IRIS Kyrgyzstan broadband network, a temporary six-station aftershock network, and a regional network operated by the Kyrgyz Institute of Seismology. The aftershocks, which range in depth from the surface to 18 km, defined a 50 ± 10-km-long rupture zone that dips 50° ± 13° to the south and strikes roughly east-west. The base of the eastern end of the aftershock zone shallowed to the east along strike and may represent a lateral ramp. The surface ruptures also had an east-west strike and dipped south, but the total length (less than 4 km) was much shorter than the aftershock zone. A teleseismic body-wave inversion, using a point source and a directivity correction, yields a focal mechanism with a strike of 221°, dip of 46°, and a slip of 43°. We obtained a moment of 4.1 × 1019 N-m with a centroid depth between 5 and 21 km. The rupture propagated along an azimuth of 330° ± 60°, which matches the relative location of the mainshock with respect to the aftershock zone. The results of the aftershock study and teleseismic inversion yield a clear picture of the fault geometry of a large-thrust earthquake.