Patterns of stress drop in earthquakes of the Northern Tien Shan

Source parameters of local earthquakes that occurred between 1998 and 2012 within the Kyrgyz seismological network (KNET) are used to study the patterns of stress drop in the Northern Tien Shan. The dynamic parameters of source radius r, the seismic moment M0, and the stress drop Ao are estimated for eighty seven M = 3.0-5.5 (K = 9.5-13.7) events, which make up 86% of earthquakes with this magnitude (99) for the period of observations. Earthquake mechanisms are determined either from P-wave arrivals (66 events) or by inversion (14 events). The distribution of earthquake mechanisms with the maximum (14 events) and minimum (14 events) stress drop shows that the amount of released stress correlates with slip geometry and revere-slip events contribute the most to the stress drop in the area. The spatial distribution of events with Ao > 0.9 MPa is compared with maps of kinematic parameters (Lode-Nadai coefficient or stress ratio, qo, and strain angle, o, based on average strain tensors according to the complete earthquake catalog for the Northern Tien Shan (1056 events for 1998-2012). The two sets of source parameters (r, M0, Ao and jio, o) correlate within the eastern Kyrgyz Range and the Karamoinok and Syndyk Ranges. © 2016, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.