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_Journal of Structural Geology 32 (2010) 1046-1060_ Contents lists available at ScienceDirect Journal of Structural Geology journal homepage: www.elsevier.com/locate/jsg Active faulting, earthquakes, and restraining bend development near Kerman city in southeastern Iran Richard Thomas Walker a,*, Morteza Talebian b, Sohei Saiffori c, Robert Alastair Sloan d, Ali Rasheedi c, Natasha MacBean e, Abbas Ghassemi b a Department of Earth Sciences, University of Oxford, Parks Road, Oxford OX1 3PR, UK b Geological Survey of Iran, Azadi Square, Meraj Avenue, P.O. Box 11365-4563, Iran c Geological Survey of Iran, Kerman Office, Kerman, Iran d Bullard Laboratories, University of Cambridge, Madingley Road, Cambridge CB3 0EZ, UK e Department of Geography, University College London, Gower Street, WC1E 6BT, London Article info Article history: Received 1 September 2009; Received in revised form 8 June 2010; Accepted 19 June 2010; Available online 14 July 2010 Keywords: Iran Active tectonics Strike-slip fault Restraining bend Earthquake hazard Abstract We provide descriptions of strike-slip and reverse faulting, active within the late Quaternary, in the vicinity of Kerman city in southeastern Iran. The faults accommodate north-south, right-lateral, shear between central Iran and the Dasht-e-Lut depression. The regions that we describe have been subject to numerous earthquakes in the historical and instrumental periods, and many of the faults that are documented in this paper constitute hazards for local populations, including the city of Kerman itself (population >200,000). Faults to the north and east of Kerman are associated with the transfer of slip from the Gowk to the Kuh Banan right-lateral faults across a 40 km-wide restraining bend. Faults south and west of the city are associated with oblique slip on the Mahan and Jorjafk systems. The patterns of faulting observed along the Mahan-Jorjafk system, the Gowk-Kuh Banan system, and also the Rafsanjan-Rayen system further to the south, appear to preserve different stages in the development of these oblique-slip fault systems. We suggest that the faulting evolves through time. Topography is initially generated on oblique slip faults (as is seen on the Jorjafk fault). The shortening component then migrates to reverse faults situated away from the high topography whereas strike-slip continues to be accommodated in the high, mountainous regions (as is seen, for example, on the Rafsanjan fault). The reverse faults may then link together and eventually evolve into new, through-going, strike-slip faults in a process that appears to be occurring at present in the bend between the Gowk and Kuh Banan faults. © 2010 Elsevier Ltd. All rights reserved. 1. Introduction We investigate the distribution of active faults around the city of Kerman in eastern Iran and the role that these active faults play in accommodating tectonic strain in the region. The faults occur in restraining bends along major strike-slip faults and are extremely well exposed due to the arid and sparsely vegetated environment of southeastern Iran. We are, therefore, able to describe the faults with a level of detail that is not possible in most actively deforming parts of the world: allowing us to investigate the general processes involved in the development of structures within restraining bends along major strike-slip fault systems. * Corresponding author. Tel.: +44 (0) 1865 272013. E-mail address: richw@earth.ox.ac.uk (R.T. Walker). 0191-8141 $ e see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jsg.2010.06.012 The region around Kerman city (population >200,000) has a long record of destructive earthquakes, with historical accounts stretching back to >1850, and with numerous instrumentally recorded events over the past >30 years including the 1981 Sirch and Golbaf earthquake sequence (e.g. Berberian et al., 1984), the 2003 Bam earthquake (e.g. Talebian et al., 2004; Jackson et al., 2006), and, most recently, the 2005 Zarand earthquake (Talebian et al., 2006). The city of Kerman, although shaken by many of the recent events, has not been subjected to heavy damage in the instrumental period. One of our aims in writing this paper is to aid future detailed studies of seismic hazard to Kerman city and its surroundings. In addition to informing estimates of seismic hazard in Iran, our results also have general application in describing well-exposed examples of restraining bend development along major active strike-slip faults. Strike-slip faults are an important component of many active regions of continental shortening (e.g. Tapponnier and Molnar, 1979; Jackson and McKenzie, 1984; Baljinnyam et al., 1993). R.T. Walker et al. Journal of Structural Geology 32 (2010) 1046-1060 1047 They accommodate this shortening either by translation (or expulsion) of material, by spatial separation (partitioning) of dipslip and strike-slip components, or through a combination of strike-slip faulting and vertical axis rotation (e.g. Allen et al., 2006). Restraining bends, where a localised component of shortening is introduced due to changes in fault strike, are a common feature of strike-slip faults in regions of tectonic shortening. The faulting within these restraining bends is often very diffuse and may evolve rapidly (e.g. Cunningham and Mann, 2007; Mann, 2007). In the following sections, we first briefly describe the tectonic and geological background of the study area. We then catalogue the many destructive earthquakes that have affected the Kerman region both historically and recently. In Section 4 we provide brief descriptions, made from both field and remote-sensing studies, of the active faults in the vicinity of Kerman city. Then, in Section 5, we describe how the population of active faults accommodate right-lateral strike-slip across eastern Iran and how they may have changed through time. 2. Geological and tectonic background 2.1. Active tectonics The active tectonics of Iran are controlled by the northward motion of Arabia relative to Eurasia, which is at a rate of ~25 mm yr-1 at longitude 56°E (Fig. 1a; Vernant et al., 2004). The GPS velocities relative to Eurasia decrease to zero at both the northern and eastern borders of Iran. This indicates that the major part of the continental shortening is confined within the political borders of the country, with the majority of the deformation concentrated in the Zagros mountains of southern Iran (Z in Fig. 1b), and in the Alborz and Kopeh Dagh mountains in the north (A and K in Fig. 1b). The arid interior of Iran (Dasht-e-Kavir, Fig. 1a) is virtually aseismic and appears to not be deforming as rapidly as its surroundings. Central Iran is moving northwards relative to western Afghanistan at a rate of ~16 ± 2 mm yr-1 at the present-day (Vernant et al., 2004). This northward motion introduces north-south, right-lateral, shear across the eastern border of the country. South of latitude 34°N this shear is accommodated on north-south right-lateral faults that surround the Dasht-e-Lut (e.g. Walker and Jackson, 2004; Meyer and Le Dortz, 2007; Walker et al., 2009). North of latitude 34°N, however, the shear is accommodated by east-west, left-lateral, faults that are thought to rotate clockwise about a vertical axis (e.g. Jackson and McKenzie, 1984). Our present study is concerned with the structures formed in the area surrounding Kerman city; in a region dominated by north-south right-lateral slip along the western margin of the Dasht-e-Lut (Fig. 2). 2.2. Geology There is a northwest-southeast structural trend present across much of central and eastern Iran. This trend follows the orientation of the Iran-Arabian suture and of the Tertiary volcanic arc that parallels it (e.g. Berberian and King, 1981). This structural trend is oblique to the roughly north-south shortening and right-lateral faulting that typifies the active deformation and it is likely that the oblique northwest-southeast trending active structures that we describe in this paper result from this pre-existing trend. The pre-existing northwest-southeast structural trend is also thought to have influenced the trend of folding and faulting within the Zagros mountains of southwest Iran (e.g. Talebian et al., 2004). The lithologies exposed in the study area are mostly Mesozoic and early Tertiary in age (GSI, 1992a, 1992b). Kuh-e-Jupar and Kuh-e-Sekonj (Fig. 2) expose a conformable Mesozoic and Tertiary sedimentary sequence. In the south of our study area, the Lalehzar and Rafsanjan faults run along the northern margin of the Sanadaj-Sirjan Tertiary volcanic belt, which consists of Eocene sediments and volcanic rocks, and which was formed during the closure of the Neo-Tethys Ocean (Dimitrijevic, 1973). The exposed rocks are likely to pre-date the onset of the late Cenozoic active tectonics, which might date from as little as 3.3 to 4.8 Ma (Walker et al., 2010). 3. Past earthquakes in the vicinity of Kerman The region surrounding Kerman has an abundant record of earthquakes both historical and modern. The main sources in the discussion of historical seismicity are Berberian (1976), Ambraseys et al. (1979), Ambraseys and Melville (1982), Berberian and Yeats (1999), and Berberian (2005). Despite Kerman's... 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