The 2011 October 23 M-w 7.2 Van-Ercis, Turkey, earthquake and its aftershocks

Abstract

On 2011 October 23, the Lake Van region in eastern Anatolia was hit by an M-w = 7.2 earthquake. The Van-Ercis earthquake (EQ) occurred 20 km east of Lake Van. Centroid moment tensors (CMT) for 108 events with M-w between 4.0 and 7.2 are computed by applying a waveform inversion method on data from the Kandilli Observatory and Earthquake Research Institute (KOERI) broad-band seismic network. The time span of data covers the period between 2011 October 23 and 2012 February 24. The main shock is a shallow focus thrust event at a depth of 15 km. Focal depths of aftershocks range from 12 to 25 km. The seismic moment (M-0) of the main shock is estimated to be 0.75 x 10(20) Nm. The focal mechanisms of the aftershocks are mainly thrust faulting with a variable and sometimes significant strike-slip component. This geometry indicates a thrust faulting regime with NE-SW trending direction of T-axis in the entire activated region. A stress tensor inversion of focal mechanism data is performed to obtain a more accurate picture of the Van-Ercis EQ stress field. The stress tensor inversion results show a predominant thrust stress regime with a NW-SE to NNE-SSW oriented maximum horizontal compressive stress (S-H). The secondary fault system striking mostly ENE-WSW is activated generally with right-lateral strike-slip in the east of the main shock. This difference in mechanism suggest that towards the east, a different fault system is activated with respect to the NE-SW trending thrust faults beneath Van-Ercis region and more to the west. Thus, to first order, the Lake Van region is characterized by a homogeneous intraplate stress field.