Geometry of co-seismic surface ruptures and tectonic meaning of the 23 October 2011 M w 7.1 Van earthquake (East Anatolian Region, Turkey) Bülent Do  gan * , Ahmet Karakas ¸ 1 University of Kocaeli, Engineering Faculty, Department of Geological Engineering, Umuttepe Campus, 41380 Kocaeli, Turkey article info Article history: Received 17 February 2012 Received in revised form 22 September 2012 Accepted 3 October 2012 Available online 5 November 2012 Keywords: 23 October 2011 Van earthquake Thrust fault Pure compressional tectonic regime Left-lateral strike-slip fault Right-lateral strike-slip fault Tensional ground cracks abstract The 23 October 2011 M w 7.1 (USGS, 2011a) Van earthquake was generated by the rupture of a main thrust fault plane striking N60  E and dipping 55  NW with a very small left-lateral offset in the western part of the Bardakçı-Saray thrust fault zone located in the north of the Bitlis-Zagros Suture Zone. The incom- patibly between the subsurface seismologic data and surface deformation data indicates that the fault that generated the earthquake could be blind. The main thrust fault plane developed between the northern (Ercis ¸ ) and southern (Van) continental blocks and indicates that the region is under the influence of a constant NWeSE pure compressional tectonic regime. Along with the primary thrust rupture, a secondary back thrust fault, a left lateral fault with NE strike and a right lateral fault with NW strike occurred in the contraction province. Additionally, the tensional ground cracks that developed on the hanging wall block of the ruptured thrust fault plane due to intra-continental collision are either transtensional that mainly fits to left lateral strike-slip faulting, or extensional deformations on the elevated block. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction The East Anatolian Region in eastern Turkey has a high morphology and is a region where the continental crust has thickened due to the collision of the Arabian and Eurasian plates (Dewey and Burke, 1973; S ¸ engör and Yılmaz, 1981; S ¸ engör et al., 2003). This collision initiated approximately 11 Ma and has been termed the Bitlis-Zagros Suture Zone (BZSZ), a structural feature that defines the boundary of the collision (Fig. 1). The Van earthquake (Magnitude-M w 7.1e 7.3) took place north of the BZSZ on 23 October 2011. The epicenter of the earthquake was at Tabanlı Village (43.36  N, 38.76  E) according to the National Earthquake Monitoring Center of Kandilli Observatory and Earthquake Research Institute-KOERI (KOERI, 2011:http:// www.koeri.boun.edu.tr). The calculated hypocenter depth of the earthquake ranged between 10 and 19 km according to different international seismological institutions. The focal mechanism solution indicated that the earthquake was generated by a major thrust fault striking 241  SW and dipping north with a minor left lateral offset (USGS, 2011a: http://earthquake.usgs.gov/ earthquakes/eqinthenews/2011/usb0006bqc/; Erdik et al., 2012). Approximately 1300 aftershocks occurred after the main shock within an area of 60  20 km, seven of which had a magnitude greater than 5.0. The earthquake created a slip plane reaching a 55 km length and 20 km depth with approximately NEeSW strike. Additionally, the focal mechanism solution of the main shock stated that the northern block (hanging wall) rose 4 m around the hypocenter while uprising ranged between 0.40 and 1.20 m on the surface (USGS, 2011b: http://earthquake.usgs.gov/ earthquakes/dyfi/events/us/b0006bqc/us/index.html). The strike of the main shock fault plane was defined 246  (N66  E) dipping 46  NW and the earthquake was created by a major thrust fault with a very small left lateral offset (Irmak et al., 2012). The surface deformations of the earthquake were mapped by several researchers during the field work and published as preliminary reports (Akyüz et al., 2011; Ça glan et al., 2011; Do gan et al., 2011; Ersoy et al., 2011; Emre et al., 2011; Özacar et al., 2011). The length of the main surface rupture was approximately 8 km and was located between Bardakçı village and southeast of As ¸ ıt village in the preliminary reports. Additionally, the northern block (hanging wall) overlapped the southern block (foot wall) along the main surface rupture. The maximum thrust offset and the maximum left lateral offset were defined 0.15 m and 0.09 m respectively during the field observations. The purpose of this study is to map and to analyze the surface deformations that developed immediately following the Van earthquake and to evaluate effects of the earthquake by other * Corresponding author. Tel.: þ90 262 3033140; fax: þ90 262 3033003. E-mail addresses: doganb3@yahoo.com, bulentd@kocaeli.edu.tr (B. Do gan), akarakas@kocaeli.edu.tr (A. Karakas ¸ ). 1 Tel.: þ90 262 3033145; fax: þ90 262 3033003. Contents lists available at SciVerse ScienceDirect Journal of Structural Geology journal homepage: www.elsevier.com/locate/jsg 0191-8141/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jsg.2012.10.001 Journal of Structural Geology 46 (2013) 99e114