The 23 October 2011 Mw 7.2 Van-Ercis, Turkey, Earthquake and Its Aftershocks

On 2011 October 23, the Lake Van region in eastern Anatolia was hit by an Mw = 7.2 earthquake. The Van-Ercis earthquake occurred 20 km east of Lake Van. Centroid moment tensors for 108 events with Mw between 4.0 and 7.2 are computed using a waveform inversion method and data from the Kandilli Observatory and Earthquake Research Institute broadband seismic network. The time span of data covers the period 2011 October 23 and 2012 February 24. The mainshock 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 (M0) of the mainshock is estimated 0.69 × 1020 Nm. The estimated source-time function shows a step-like function with a rupture duration of 38 s. 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. One of the largest aftershocks (9 November 2011 19:23 GMT, Mw = 5.8) located 30 km south of the mainshock exhibits strike-slip faulting with NE-SW trending direction of T-axes. This difference in mechanisms suggests that towards the south, a different fault system is activated with respect to the NE-SW trending thrust faults beneath Van-Ercis region and more to the north. A Stress tensor inversion of focal mechanism data is performed to obtain a more accurate picture of the Van-Ercis earthquake stress field. High variances (> 0.2) in local stress field orientations in the south prove that a different fault system in multiple orientations may be activated.