Surface rupture of the 1911 kebin (Chon-Kemin) earthquake, Northern tien shan, kyrgyzstan

Abstract

The 1911 Chon-Kemin (Kebin) earthquake culminated c. 30 years of remarkable earthquakes in the northern Tien Shan (Kyrgyzstan and Kazakhstan). Building on prior mapping of the event, we traced its rupture in the field and measured more than 50 offset landforms. Cumulative fault rupture length is >155-195 km along 13 fault patches comprising six sections. The patches are separated by changes of dip magnitude or dip direction, or by 4-10 km-wide stepovers. One <40 km section overlaps and is parallel to the main north-dipping rupture but is 7 km north and dips opposite (south). Both ends of the rupture are along mountain front thrust faults demonstrating late Quaternary activity. We computed the moment from each fault patch using the surface fault traces, dip inferred from the traces, 20 km seismogenic thickness, rigidity of 3.3 × 1010 Nm-2 and dip slip converted from our observations of the largely reverse sense of motion vertical offsets. The discontinuous patches with c. 3-4 m average slip and peak slip of <14 m yield a seismic moment of 4.6 × 1020 Nm (Mw 7.78) to 7.4 × 1020 Nm (Mw 7.91). The majority of moment was released along the inner eastern rupture segments. This geological moment is lower by a factor of 1.5 from that determined from teleseismic data.