A geodetic study of the 23 October 2011 Van, Turkey earthquake

The Van (Eastern Anatolia, Turkey) earthquake occurred on Sunday, October 23, 2011 with a moment magnitude of 7.2. The tectonics of this region is characterized by strike-slip faulting on the Bitlis Suture Zone, and thrusting in the Zagros fold and thrust belt. Using high-rate (1. second) GPS data from permanent GNSS stations from the CORS-TR network, co-seismic displacements of eleven stations were determined using precise point positioning during this earthquake. We used the time series of coordinate changes for fourteen CORS-TR stations, and calculated the crust movements before and after the earthquake. According to the PPP solutions computed using high frequency GPS data to determine the co-seismic motions of stations, we conclude for the Van earthquake an occurrence time of 10:41:22 (UTC). No pre-seismic horizontal movement of stations at the level more than 5. mm before the earthquake could be observed. That means that no kinematic warning or prediction before the earthquake exists. Along an east-west horizontal line north of the Van Sea with a length of about 100. km, the northern part of this line experienced extension of 0.2-1. ppm in a NW-SE direction. The southern part experienced N-S shortening of 0.5-1.5. ppm. The N-S shortening we estimated geodetically matches well with the N-S shortening and thrust focal mechanism derived independently using seismic data by the USGS. Co-seismic surface displacements derived from the GPS data are consistent with the teleseismic source model given by the USGS. The geodetic source model derived from the GPS data reproduces the same moment magnitude and centroid as the teleseismic model, but shows a higher spatial resolution of the slip distribution. We also analyzed the post-seismic surface displacements derived from the GPS data within the first two weeks after the mainshock. No reasonable slip distribution on the co-seismic fault plane could be found, indicating that the sources for the early post-seismic deformation might come from the widely scattered aftershocks.