A recent example of continent-continent collision : October 23, 2011 Van Earthquake (Mw=7.2) : Southeastern Turkey

The Eastern Anatolia region is one of the best examples of a continental collision zone in the world. The tectonics of the Lake Van region is dominated by the active convergence of the Arabian and Eurasian plates.The southeast border of the Anatolian plate with the Arabian plate is Bitlis Suture Zone. This zone is formed by collision of Arabian-and in large scale Eurasian plates at mid-Miocen age. This type of thrust generation as a result of compressional regime extends east-west. On 23 October 2011 at 13:41(local time) a strong earthquake (Mw=7.2) occurred in east of Lake Van. The earthquake destroyed the regions especially between the cities of Van and Ercis, and East of Lake Van-Lake Ercek region. It caused deaths of 600 people and more than 4150 people were injured with tens of thousands rendered homeless. In addition, 40 people died in the earthquake of September 9, 2011 Edremit-Van (Mw=5.7). The initial rapid fault solution shows that the rupture started at 43.41(deg.) North -38.72 (deg.) East coordinates. The fault that caused the Van earthquake is a reverse fault with a northward dipping fault plane. After the main shock 11 important earthquakes (5.0≤M≤6.0) were occurred in the region which have hypocentral distances of 8-38 km. from the main shock location. These earthquakes have shallow epicenters and they have less than 16 km depth. In general, the distribution of the aftershocks show high activity along the east-northeast of Lake Van and the northern part of the Van city. The distribution of the important earthquakes and the aftershock distribution shows that the E-W and NE-SW oriented fault segments cause the earthquake activities. Stress increase and related triggered seismic activity were observed at NE-SW and NW-SE oriented directions of the east-west trending fault that was broken during Van Earthquake. Indeed, November 9, 2011 Edremit-Van Earthquake (Mw=5.7) is considered to be triggered by the mainshock. Stress change and breakage of the secondary faults led aftershocks lasting longer time period than usual. The results of strain analysis show that the general alignment of the largest strain axis (P-compressional) has N-S (NNW/SSE) and tensional axis (T-dilatation axis) has E-W (ENE-WSW) direction. The distribution of the important earthquakes and the aftershock distribution shows that the E-W and NE-SW oriented fault segments cause the earthquake activities. The b-value analysis is done for the earthquakes occurred in the region, to find out if there is a relationship between the relationship between the faulting type and faulting type and dominant tectonic regime. b-value associated with the current continuing compression regime that has been tested and found a lower b-value. Van earthquake and over 20 important aftershocks fault mechanism solutions show that the region is under compression and reverse faulting is a result of this regime which is effective on the active tectonics of the region. Van earthquake is a good example of the dominant compressional tectonic regime in Southeast Anatolia which caused blind reverse faulting as a result. This study showed that upper crust is seismogenic in the Southeastern Anatolia that causes seismic activity. This work was supported by Bogazici University Research Fund within the scope of project BAP/SRP 6671.