Asperity of the 2013 Lushan earthquake in the eastern margin of Tibetan Plateau from seismic tomography and aftershock relocation

Abstract

SUMMARY The Mw 6.6 Lushan earthquake occurred on 2013 April 20 in the eastern margin of Tibetan Plateau, and was about 50km away from the 2008 Mw 7.9 Wenchuan earthquake rupture zone. By using arrival times from portable and permanent seismic stations, local earthquake tomography and aftershock relocation were conducted by using 41955 first P and 42687 first S arrivals. Low-Vp/Vs, high-Vp and Vs anomaly are found in the source region, which is well consistent with the aftershock distributions. The ruptured fault plane might be a blind thrust and is well defined by the Vp/Vs structure and aftershock seismicity. High-velocity and lowVp/Vs anomalies may suggest the mafic or ultramafic materials thrust from mid-lower crust, and define the asperity that concentrated stresses responsible for seismogenesis. In contrast, low-Vs anomalyisfoundinthegapbetweentheWenchuanandLushanearthquakes,suggesting of ductile rocks with low stress.