The neotectonics of southeast Turkey, northern Syria, and Iraq: the internal structure of the Southeast Anatolian Wedge and its relationship with recent earthquakes

In southeastern Turkey, northern Syria, and Iraq, the Southeast Anatolian Wedge (SEAW) is recognized as lying between the high altitude Bitlis–Zagros Suture Zone and the Sincar Mountains on the Mesopotamian plain. This wedge narrows towards the south and contains several thrust and blind thrust zones merging with the basal thrust zone.

Turkish Journal of Earth Sciences Turkish J Earth Sci (2017) 26: 105-126 © TÜBİTAK doi:10.3906/yer-1605-21 http://journals.tubitak.gov.tr/earth/ Research Article The neotectonics of southeast Turkey, northern Syria, and Iraq: the internal structure of the Southeast Anatolian Wedge and its relationship with recent earthquakes 1, 1 Gürol SEYİTOĞLU *, Korhan ESAT , Bülent KAYPAK Department of Geological Engineering, Tectonics Research Group, Ankara University, Gölbaşı, Ankara, Turkey Department of Geophysical Engineering, Ankara University, Gölbaşı, Ankara, Turkey Received: 26.05.2016 Accepted/Published Online: 10.02.2017 Final Version: 15.06.2017 Abstract: In southeastern Turkey, northern Syria, and Iraq, the Southeast Anatolian Wedge (SEAW) is recognized as lying between the high altitude Bitlis–Zagros Suture Zone and the Sincar Mountains on the Mesopotamian plain This wedge narrows towards the south and contains several thrust and blind thrust zones merging with the basal thrust zone These zones are determined mainly by locations of fault-propagation folding that generally limit the Plio-Quaternary/Quaternary plains in the region The positions of these active thrust/blind thrust zones and their relationships to the right and left lateral faults may be used to explain the seismic activity of the region Key words: Neotectonics, southeast Turkey, Syria, Iraq, earthquake, thrust Introduction The neotectonics of southeastern Turkey began after the collision of Arabian and Eurasian plates along the Bitlis– Zagros suture zone (Şengör, 1980; Şengör and Yılmaz, 1981; Şengör et al., 1985) The collision history starts during the Late Maastrichtian–Early Eocene and final contact of the continents and formation of the zone of imbrications take place in Late Miocene times (Hall, 1976; Şengör and Kidd, 1979; Aktaş and Robertson, 1984; Yılmaz, 1993) Recently, Robertson et al (2016) distinguished three main tectonic phases in Southeastern Turkey: during the Late Campanian, Early Eocene, and Early Miocene The intracontinental convergence is also continuing in the present day (Şengör and Kidd, 1979; Şaroğlu and Güner, 1981; Allen et al., 2004; Reilinger et al., 2006; Aktuğ et al., 2016) In contrast to the earlier evaluations of thick continental crust (e.g., 55 km, Dewey et al., 1986), recent studies demonstrate that eastern Turkey has a 45-kmthick crust with an accretionary complex supported by asthenospheric cushioning (Keskin, 2003; Şengör et al., 2003, 2008) Tectonic studies have mainly focused on the structures located in the north of the Bitlis–Zagros suture zone (Yiğitbaş and Yılmaz, 1996; Oberhanslı et al., 2010; Okay et al., 2010) but the structures of the Arabian foreland were poorly studied (Lovelock, 1984; Biddle et al., 1987; * Correspondence: seyitoglu@ankara.edu.tr Perinỗek et al., 1987; Gilmour and Makel, 1996) and only the fold axes are shown on the maps (Şengör et al., 1985, 2008; Yılmaz, 1993; Okay, 2008) The Zagros foreland, however, is relatively well studied in terms of blind thrusting, seismicity, and GPS data (Berberian, 1995; Hatzfeld et al., 2010; Agard et al., 2011) (Figure 1) The existing active fault map of Turkey (Emre et al., 2013) does not explain the correlation with all seismic events, especially in southeastern Turkey Most of the active faults are of a strike–slip nature and are recognized after major earthquakes in eastern Turkey (i.e Çaldıran, Varto, Bingưl) Active thrust fault lines are rare on the MTA map, with the exception of the Bitlis Suture Zone, and the Van and Cizre Faults, whose limited identification is probably due to thrust-related major earthquakes For example, the 1975.09.06 Lice earthquake (Ms: 6.7) was attributed to the Bitlis Suture Zone (Arpat, 1977; Jackson and McKenzie, 1984) The Van Fault Zone was recognized and mapped after the 2011.10.23 Van earthquake (Mw: 7.1) (Zahrandik and Sokos, 2011), which taught us that blind thrusts are important seismic sources in eastern/southeastern Turkey and that they need to be studied in detail Southeastern Turkey presents several thrusts/blind thrusts that can be determined by using asymmetrical fold axes (Suppe, 1983; Mitra, 1990; Suppe and Medwedeff, 1990) We interpret these structures, together with their counterparts in northern Syria and Iraq, as having 105 SEYİTOĞLU et al / Turkish J Earth Sci Figure Neotectonics of southeastern Turkey, northern Syria, and northern Iraq Digital elevation model is obtained from the SRTM arc-second data Black lines are active structures outside of the SEAW Red solid lines with triangles on the hanging wall are thrust faults; dotted dashed lines represent the blind thrusts Normal faults are shown by a rectangle on the hanging wall Strike–slip faults are shown with half arrows Plio-Quaternary/Quaternary deposits are shown by the gray areas adapted from Günay and Şenel (2002), Turhan et al (2002), Ulu (2002), Şenel and Ercan (2002), Tarhan (2002), Krasheninnikov (2005), and ASGA-UNESCO (1963) DSFZ: Dead Sea Fault Zone (Hall et al., 2005; Krasheninnikov et al., 2005), EAFZ: East Anatolian Fault Zone, NAFZ: North Anatolian Fault Zone (Şaroğlu et al., 1992) BZSZ: Bitlis Zagros Suture Zone (Emre et al., 2013) I- Yavuzeli Blind Thrust Fault (YBT); II- Araban Blind Thrust Fault (ABT); III- Çakırhüyük Blind Thrust Fault (ÇBT); IV- Halfeti Fault (HF); V- Adıyaman Thrust Zone (ATZ); VI- North Karacadağ Fault (NKF); VII- Karacadağ Extensional Fissure (KEF); VIII- South Karacadağ Fault (SKF); IX- Mardin Blind Thrust Zone (MBTZ); X- Ergani–Silvan Blind Thrust Fault (EBT); XI- Raman Thrust Fault (RTF); XII- Garzan Thrust Fault (GTF); XIII- Cizre Thrust Fault (CTF); XIV- Silopi Blind Thrust Fault (SBT); XV- Bikhayr Blind Thrust Zone (BBTZ); XVI- Sincar–Kerkük Blind Thrust Zone (SBTZ); XVII- Muş Thrust Fault (MTF); XVIII- Van Thrust Fault (VTF); XIX- Bozova Fault (BOF) XX- Başkale Fault (BKF); XXI- emdinliYỹksekova Fault (YF); AG- AkỗakaleHarran Graben; N-S: Location of regional cross section; B-B’: Magnetotelluric data location of Türkoğlu et al (2008) The western continuation of XVI (SBTZ) is drawn according to subsurface data presented in Litak et al (1997- Figure 14) developed in the Southeast Anatolian Wedge (SEAW) The cross-sectional geometry is very similar to that of a tectonic wedge occurring in accretionary prisms above subduction zones (Figure 2) The tectonic wedges mimic a wedge-shape pile of snow in front of a snowplow The shape of the wedge is related to (1) the applied force, (2) the friction on the basal thrust, (3) the internal strength of the material in the wedge, and (4) the erosion of the surface of the wedge (see Dahlen, 1990 for a review) In this paper, we aim to contribute to the understanding of the SEAW We particularly examine major asymmetrical folds in the region using Google Earth images, because they would indicate the location of thrust/blind thrust faulting All these structures will provide information 106 about the internal structure of the SEAW that may supply logical explanations for the thrust-related seismic activity recorded in the instrumental period, such as the 1975.09.06 (M:6.7) Lice and 2012.06.14 (M:5.5) Şırnak– Silopi earthquakes The structure of the SEAW in the Arabian foreland The SEAW is located between the Bitlis–Zagros Suture Zone (BZSZ) and Sincar Mountain in Iraq (Figure 1) Its southern tip is represented by the Sincar–Kerkük Blind Thrust Zone (SBTZ) The SEAW is mainly composed of several thrust/blind thrust faults and related folds with some strike–slip faulting The reverse and/or thrust faults that reach the surface are marked by continuous red lines SEYİTOĞLU et al / Turkish J Earth Sci Figure Tectonic wedge geometry (after Dahlen, 1990) with triangles on the upthrust (hanging wall) side in the maps presented in this paper The red broken dotted lines represent the approximate surface trace of blind thrusts that is located in front of the forelimb An asymmetrical fold is determined by the short or long drainage system together with the blunt or sharp “v” of bedding traces in the Google Images (Figure 3) Quaternary deposits unconformably cover various earlier lithostratigraphical units including an Upper Miocene unit containing mammalian fossils (Kaya et al., 2012) in SE Turkey The internal structure of the SEAW is explained below, from west to east Gaziantep area: to the NNW of the city of Gaziantep, three prominent E–W trending plains are distinguished, namely the Yavuzeli, Araban, and Çakırhüyük plains (Figure 4a) The linear E–W trending northern border of the Yavuzeli plain separates Quaternary deposits in the south and Miocene limestones in the north (Ulu, 2002) Two different drainage systems are recognized on the limestones: south flowing drainages are shorter than the north flowing one (Figures 4a–4c) This feature indicates an asymmetrical anticline that may be related to a blind thrust (Figure 4d) A similar blind thrust is reported further to the south, just north of Kilis (Coşkun and Coşkun, 2000) For this reason, identical structures are expected on the north of the Araban and Çakırhüyük plains (Figure 4a–4e) They are bounded from the west by the NE–SW trending left lateral East Anatolian Fault Zone and in the east the left lateral Halfeti Fault cuts asymmetrical anticlines (Figure 4a) The Adıyaman Thrust Zone (ATZ) is located to the north of the Halfeti Fault (Figures 5a and 5b) The Eocene units on the north thrust over Plio-Quaternary deposits (Ulu, 2002) on the south along with ATZ via Narince The Halof dağı asymmetric anticline is located on the hanging wall of the ATZ, as shown on the geological cross section of Sungurlu (1974) (Figure 5c) The limbs of the Halof dağı asymmetric anticline are clearly seen in Google Earth images, where the anticline is seen to be partly eroded in Pınaryayla (Figure 5d) Their control of the topography of the region indicates that the ATZ and north dipping normal faults must be young structures (Figure 5e) West of Diyarbakır: to the east of Narince, between the villages of Ceylan and Yayıklı, a branch of active faulting is separated from the ATZ This NW–SE trending right lateral North Karacadağ Fault (NKF) (Emre et al., 2012) is connected to the N–S trending Karacadağ Extensional Fissure (KEF) (Şengör et al., 1985; Şaroğlu and Emre, 1987) We suggest that the KEF might be connected to the Mardin Blind Thrust Zone (see next section) by a NW–SE trending right lateral strike–slip South Karacadağ Fault Figure Blind thrust and fault-propagation fold with morphological features 107 SEYİTOĞLU et al / Turkish J Earth Sci Figure (a) Neotectonic structures on the north of Gaziantep See Figure for the location Plio-Quaternary/Quaternary deposits are shown by the dark gray/gray areas respectively and adapted from Ulu (2002) Topography is obtained from the SRTM arcsecond data Dotted line represents the basal thrust of the SEAW Broken dotted lines are the surface trace of blind thrusts EAFZ: East Anatolian Fault Zone; ÇBT: Çakırhüyük Blind Thrust Fault; ÇP: Çakırhüyük Plain; ABT: Araban Blind Thrust Fault; AP: Araban Plain; YBT: Yavuzeli Blind Thrust Fault; YP: Yavuzeli Plain; HF: Halfeti Fault (b) Typical drainage pattern on the hanging wall of YBT (c) Google Earth image of the hanging wall of YBT South dipping beds (orange lines) of Miocene limestones and a sharp contact with the Quaternary Yavuzeli Plain (d) The cross section of Y-Y’ indicating asymmetrical anticline on the hanging wall of YBT (e) Z-Z’ topographical cross section of Çukurhüyük, Araban, and Yavuzeli plains and interpretation of the blind thrusts (SKF) (Figure 6) The overall structure of the KEF is a releasing bend between the NW–SE trending right lateral strike–slip North and South Karacadağ faults that play the role of a tear fault between the ATZ and the Mardin Blind Thrust Zone (Figure 6) While the NKF and KEF may be clearly followed on the topography and are mapped as Quaternary faults (Emre et al., 2012), the trace of the SKF corresponds to the locations of the parasitic cones of the Karacadağ volcano (Figure 6) that is drawn as a continuous right lateral fault by using information from the shorter strike–slip segment on the geological map given by Turhan et al (2002) Mardin area: the Mardin Blind Thrust Zone (MBTZ) can be drawn by following the asymmetrical anticline axes 108 in the region The high angle southern limbs of the anticline are limited by Quaternary and/or Plio-Quaternary deposits (Turhan et al., 2002) (Figures 7a and 7b) A close-up view around the city of Mardin indicates that the city is located on the axis of a south verging asymmetrical anticline Cretaceous neritic limestone is exposed in the core of this anticline The Eocene limestones have steep dipping beds towards the south and are limited by the Quaternary fill of the Mesopotamian plain (Turhan et al., 2002) (Figure 7c) The axes of these asymmetrical anticlines are en echelon in nature that might be the reflection of several splays of the MBTZ (Figures 7a and 8a) The MBTZ was shown on the maps given by Lovelock (1984) and Perinỗek et al (1987) and in the cross section reported by Krasheninnikov SEYİTOĞLU et al / Turkish J Earth Sci Figure (a and b) The Adıyaman Thrust Zone (ATZ) between Adıyaman and Narince For location see Figure EAFZ: East Anatolian Fault Zone; BZSZ: Bitlis Zagros Suture Zone Plio-Quaternary/Quaternary deposits are shown by the dark gray/gray areas respectively and adapted from Ulu (2002), Tarhan (2002), and Turhan et al (2002) Topography is obtained from the SRTM arc-second data (c) D-D’ geological cross section across the Adıyaman Thrust Zone (ATZ) Modified and simplified from Sungurlu (1974) (d) Cross-sectional view of Halof Dağı asymmetrical anticline, Google Earth image looking east near Pınaryayla (e) X-X’ topographical cross section of Halof Dağı and relationship between asymmetric anticline and ATZ (2005) The E–W trending MBTZ bends to the NE–SW between Nusaybin and İdil (Figure 8a) and continues to the west of Cizre This zone can be traced along the border of the S and SE dipping Eocene limestone unit and the Quaternary deposits of the Mesopotamian plain but it cannot be followed further NE due to the Quaternary basalt lava flow around İdil (Turhan et al., 2002) (Figure 8a) North of MBTZ: to the north of Mardin, the Raman Thrust Fault (RTF) is shown on geological maps (Turhan et al., 2002; Yıldırım and Karadoğan 2011) and on the cross section reported by Lovelock (1984) There is a major asymmetrical fold axis on its hanging wall at Raman Dağı (Figures 8a–8c) The steeply dipping southern limb and shallow dipping northern limb are clearly seen on the Google Earth images (Figures 8b and 8c) The Pleistocene uplift of the structure, due to the RTF, is represented by three different alluvial terraces seen only on the northern slopes of the Dicle river north of Hasankeyf (Yıldırım and Karadoğan, 2005) (Figure 8b) Further to the north, the NW–SE trending Garzan Thrust Fault (GTF) is responsible for the formation of the Garzan asymmetric anticline (Figures 8d and 8e) The anticline axis and thrust fault are nearly parallel to each other, lying N 65 W The northern limb of the anticline dips 15° while the southern limb has a steeper dipping, slanting up to 75°, and is locally overturned (Sanlav et al., 1963; Ketin, 1983) The thrust fault dips 55° towards the NE and has a 600 m vertical throw (based on correlation of wells 43 and 47) that dies out towards the NW and SE 109 SEYİTOĞLU et al / Turkish J Earth Sci Figure NW–SE trending North Karacadağ (NKF) and South Karacadağ (SKF) faults and the position of Karacadağ Extensional Fissure (KEF) as a releasing bend See Figure for location Circles are the locations of parasitic cones of the Karacadağ volcano Plio-Quaternary/Quaternary deposits are shown by the dark gray/gray areas respectively and adapted from Turhan et al (2002) and Tarhan (2002) Topography is obtained from the SRTM arc-second data (Sanlav et al., 1963) (Figure 8f) Further to the SE, in front of its steeply dipping limbs, well developed Quaternary deposits (Turhan et al., 2002) demonstrate that this is a neotectonic structure Another prominent structure is the Ergani–Silvan Blind Trust Fault (EBT) determined by the south dipping beds that can be seen on Google Earth images The axis of the asymmetric anticline is parallel to the thrust zone, which limits the Quaternary deposits particularly to the south of Ergani (Tarhan, 2002) (Figure 9a) This thrust zone is also the best source candidate for the 1975.09.06 (Ms: 6.7) Lice earthquake (see below) The EBT was recognized by Gilmour and Makel (1996) in whose study the EBT and related fault-propagation folds were clearly seen in seismic reflection sections The Hazro asymmetric anticline is located on the hanging wall of the EBT (Figures 9a–9c) The axis of the Hazro anticline is eroded and the Silurian beds are exposed (Ketin, 1983) (Figure 9b) The Cizre–Silopi area: the WNW–ESE trending Cizre Thrust Fault (CTF) is shown on the MTA’s active fault map (Duman et al., 2012) and continues toward northern Iraq (Figure 10a) The CTF separates into a middle Triassic– Upper Cretaceous Cudi Group and lower–middle Eocene units (Schmidt, 1964) In the hanging wall of the thrust, the Cudi group creates an asymmetric anticline and the footwall is composed of nearly vertical or overturned 110 Eocene units (Figure 10b) To the NE of Silopi, the tilted Miocene beddings are in contact with Quaternary alluvial fan deposits (Günay and Şenel, 2002) that indicate the Silopi Blind Thrust Fault (SBT) and this structure continues to the east towards Derker Ajam (northern Iraq) (Figure 10a) Further south, the anticline at the Bikhayr mountains (Ameen, 1991) in the south of Zaho (Iraq) and south of Al-Malikiyah (Syria) indicates another blind thrust zone named the Bikhayr Blind Thrust Zone (BBTZ) This can be traced from Tepke (Syria) (Kent, 2010) to Dohuk (Iraq) via Dayrabun (Iraq) No certain relationship between these structures has been established by using Google Earth images but the BBTZ, the MBTZ, and the CTF overlap each other around Al-Malikiyah and İdil (Figure 10a) All the structures in the Cizre–Silopi area are assumed to be connected by a basal thrust and their relationships with each other and with the topography are shown in Figure 10c The Sincar and Abdülaziz Mountains: Sincar Mountain in Iraq is located 92 km south of the Mardin Blind Thrust Zone (Figures and 11a) The overall structure of Sincar Mountain is a closed anticline, but a more detailed look reveals that it has a small syncline on the axis of a huge anticline (Figure 11b) The drainage pattern and shape of V’s of the bedding in both limbs of the anticline indicate that the northern limb has a higher dip value than the southern limb (see also the subsurface data reported by SEYİTOĞLU et al / Turkish J Earth Sci Figure (a) Mardin Blind Thrust Zone (MBTZ) having several segments Broken dotted lines are the surface trace of the blind thrust Plio-Quaternary/Quaternary deposits are shown by the dark gray/gray areas respectively and adapted from Turhan et al (2002) Topography is obtained from the SRTM arc-second data (b) Google Earth image immediately south of Mardin Rule of V’s indicates south dipping beds (orange lines) and sharp contact with the Plio-Quaternary deposits (c) W-W’ topographical cross section of Mardin area and simplified asymmetric anticline and its relationship with the interpreted blind thrusting Brew et al., 1999), which is dissimilar to the dip features of the anticlines in southeast Turkey; this is probably due to back thrusting under the northern limb of the Sincar anticline (Figure 11c) We evaluate that the Sincar anticline was created by the Sincar–Kerkük Blind Thrust Zone (SBTZ), representing the southernmost tip of the SEAW This is followed towards the south of Musul via Tel Afer to the east (Kent, 2010) and towards Abdülaziz Mountain to the west (Figure 1) Abdülaziz Mountain has a similar, but less prominent, structure (Sawaf et al., 1993; Kent and Hickman, 1997; Rukieh et al., 2005) to Sincar Mountain (Brew et al., 1999; 2001) The northern margin of Abdülaziz Mountain is limited by a south dipping thrust fault (Sawaf et al., 1993; Kent and Hickman, 1997; Kazmin, 2005) that can be interpreted as a back thrusting similar to that of Sincar Mountain The geomorphological map of Syria compiled by K Mirzayev (Krasheninnikov, 2005) indicates that Abdülaziz Mountain is surrounded by upper Quaternary and recent alluvial fans The western edge of Abdülaziz Mountain is probably connected to the AkỗakaleHarran graben, with strike slip faulting (the Abba fault of Lovelock, 1984) that is subparallel to the Bozova Fault (BOF) In this case, it is interesting to see that a more evolved and similar structure developed with the NKF, the KEF, and the SKF (Figure 1) All the observations explained above demonstrate that there is the SEAW in front of the BZSZ and its southern tip is located in the Sincar–Kerkük Blind Thrust Zone Morphometric analysis (mountain front sinuosity) In order to evaluate the tectonic activity along thrust/blind thrust faults, mountain front sinuosity (Smf ) values were determined as morphometric analysis (Figure 12) Smf is defined as Smf = Lmf/Ls, where Lmf is the length of the mountain front along the mountain range–basin boundary and Ls is the straight-line length of the same front (Figure 12a) (Bull and McFadden, 1977) 111 SEYİTOĞLU et al / Turkish J Earth Sci Figure (a) Eastern continuation of the Mardin Blind Thrust Zone (MBTZ) and the positions of Cizre Thrust Fault (CTF), Raman Thrust Fault (RTF), and Garzan Thrust Fault (GTF) For location see Figure Broken dotted lines represent the surface trace of the blind thrusts Plio-Quaternary/Quaternary deposits are shown by the dark gray/gray areas and adapted from Turhan et al (2002), Günay and Şenel (2002), and Tarhan (2002) Topography is obtained from the SRTM arc-second data (b) The detail of Raman Thrust Fault at the north of Hasankeyf The traces of bedding (orange lines) on the Google Earth image indicate Raman asymmetric anticline The terraces located on the northern slopes of Dicle River (oldest -T1: 60–80 m, T2: 30–50 m, youngest -T3: 8–10 m from the valley floor) are adapted from Yıldırım and Karadoğan (2005) (c) The relationship asymmetric Raman anticline and Raman Thrust Fault on the V-V’ topographical cross section (d) Close up Google Earth image of Garzan Thrust Fault (e) The traces of bedding (orange lines) indicate asymmetrical anticline on the Google Earth image according to rule of V’s (f) C-C’ geological cross section across the GTF (after Sanlav, 1963; Ketin, 1983) 112 SEYİTOĞLU et al / Turkish J Earth Sci Figure (a) Map of Ergani–Silvan Blind Thrust (EBT) Eastern part of the EBT is adapted from Gilmour and Makel (1996) See Figure for location Broken dotted line represents the surface trace of the blind thrusts Plio-Quaternary/Quaternary deposits are shown by the dark gray/gray areas and adapted from Turhan et al (2002) and Tarhan (2002) Topography is obtained from the SRTM arc-second data (b) Geological cross section of Hazro asymmetric anticline (Ketin, 1983) (c) Relationship between Hazro asymmetric anticline and Ergani–Silvan Blind Thrust Fault Mountain front sinuosity is related to erosional processes and tectonic activity Tectonically active fronts generally have straight mountain range–piedmont (basin) junctions Smf values lower than 1.4 indicate high tectonic activity (Rockwell et al., 1984; Keller, 1986) In the present study, we performed Smf analysis on the mountain fronts that are related to the thrust/blind thrust fault segments (Figures 12b–12m) The analysis shows that the Smf values of most of the segments are lower than 1.4 (Figure 12n) This result indicates that the faults are tectonically active in the region supported by the thrustrelated seismic activity (see next section and Table), where the GPS results show 17.8 ± 1.1 mm/year contraction (Reilinger et al., 2006) Only some parts of the MBTZ have values higher than 1.4 and these segments can accordingly be evaluated as tectonically less active (Figure 12k) Seismotectonics of southeastern Turkey, northern Syria, and Iraq The epicenter distribution of the earthquakes from the Boaziỗi University Kandilli Observatory and Earthquake Research Institute (KOERI, 1900–2015) strongly documents some clusters in the region (Figure 13) It can easily be recognized that the left-lateral strike–slip East Anatolian Fault Zone (EAFZ) and the right-lateral North Anatolian Fault Zone (NAFZ) are the main sources of earthquake occurrences in the region The second important earthquake cluster in the area is related to the 2011.10.23 Van earthquake (Mw: 7.1), which was created by a blind thrust (see below) It is important to note that until this recent Van earthquake, only the 1975.09.06 Lice earthquake (Ms: 6.7) was known as a major event related to thrust faulting in the region 113 SEYİTOĞLU et al / Turkish J Earth Sci Figure 10 (a) Map of the Cizre Thrust Fault (CTF), the Silopi Blind Thrust Fault (SBT), the Bikhayr Blind Thrust Zone (BBTZ), and the eastern end of Mardin Blind Thrust Zone (MBTZ) For location see Figure Broken dotted lines are the surface trace of the blind thrusts Plio-Quaternary/Quaternary deposits are shown by the dark gray/gray areas and adapted from Günay and Şenel (2002) and Turhan et al (2002) Topography is obtained from the SRTM arc-second data (b) Geological cross section across the CTF (Schmidt, 1964) (c) T-T’ topographical cross section and relative positions of the CTF, the SBT, and the BBTZ Dotted line represents the basal thrust of the SEAW For this reason, Ambraseys (1989) refers to the existence of a quiescent period during the 20th century Before the 2011 Van earthquake, seismicity data give an impression that right- and left-lateral strike–slip faults produced most of the earthquakes in the south of the BZSZ (Figure 13) The third earthquake cluster is related to the right lateral Bozova Fault and the marginal faults of the Akỗakale/ Harran Graben, the forth seismic intensity seems to be related to the dextral Yüksekova–Şemdinli Fault, and the fifth seismic intensity can be recognized around Silopi The 2012.06.14 Şırnak–Silopi earthquake (Mw: 5.1) (see below) indicates that the E–W thrusting (Bikhayr Blind Thrust Zone) is also a major neotectonic structure capable of producing major seismic events (Figure 13) 114 In the NE of Syria, the sixth seismic cluster of moderate earthquakes is located around Haseki This cluster is probably related to a NW–SE trending right-lateral tear fault in the Sincar–Kerkük Blind Thrust Zone It should be noted that our evaluation contradicts the interpretation given by Abdul-Wahed and Al-Tahhan (2010), whose study suggested E–W trending left-lateral strike–slip faulting in this region The focal depths of all catalog events (from 1900 to 2015) for this region indicate that generally most of the events occurred in the crust (upper 30 km) However, we observe that there are several deep earthquakes located as far down as 170 km Their quantity is very low relative to the crustal events Especially after the year 2000, which saw SEYİTOĞLU et al / Turkish J Earth Sci Figure 11 (a) Location of the Sincar–Kerkük Blind Thrust Zone (SBTZ) See Figure for the location Broken dotted lines are the surface trace of the blind thrusts Quaternary deposits are shown by the gray areas and adapted from ASGA-UNESCO (1963) Topography is obtained from the SRTM arc-second data (b) Cross-sectional view of Google Earth image of Sincar Mountain Looking east Note a small syncline on the top of the mountain (c) Topographical cross section of Sincar Mountain and the relationship between anticline structure and thrusting (after Brew et al., 1999) the start of the Turkish national seismic network expansion studies, the rate of such deeper events is gradually reduced; this is due to increased quality and quantity of observation To be able to interpret the internal structure of the SEAW, many focal mechanism solutions referring to selected earthquakes were either calculated or collected from several catalogs and publications A full data set is presented in the Table We calculated the focal mechanism solutions for selected events in the region (Figure 13; Table) We selected magnitudes (ML) of the events varying in a range between 3.4 and 4.9 These events occurred between 2004 and 2015 They were firstly relocated and then their source parameters were calculated by using a moment tensor inversion method Therefore we processed the time domain regional moment tensor inversion following Herrmann et al (2011) in order to obtain the source depth, moment magnitude and strike, and dip and rake angles of a shear-dislocation source, using three-component broadband waveforms The waveform data pole-zero files were retrieved from the KOERI data archive The main idea in this method is to fit synthetic waveforms to observed seismograms at local and regional stations The synthetic Green’s functions were computed as suggested in Herrmann et al (2011) Both the observed and Green’s function ground velocities were cut from a range of 5–10 s before the P-wave’s first-arrival to a range of 110–180 s after it In the inversion process a three-pole causal Butterworth bandpass filter changing with a 0.02–0.11 Hz band range was used for the events Additionally, an optional microseism rejection filter was applied to enhance the signal-to-noise ratio when needed We eliminated noisy and problematic signals; furthermore, waveform data recorded by stations beyond 700 km were deselected After the moment tensor inversion process, we determined the source parameters of 28 events They are given in the Table and shown in Figure 13 The overall epicentral distributions and available focal mechanism solutions of the earthquakes demonstrate that 115 SEYİTOĞLU et al / Turkish J Earth Sci Figure 12 Mountain front sinuosity related to the thrusts/blind thrusts (a) Definition of Smf (Bull and McFadden, 1977) (b) Yavuzeli Blind Thrust (YBT) (c) Araban Blind Thrust (ABT) (d) Çakırhüyük Blind Thrust (ÇBT) (e–f) Mardin Blind Thrust Zone (MBTZ) (g) Ergani–Silvan Blind Thrust (EBT) (h) Bikhayr Blind Thrust Zone (BBTZ) (i) Silopi Blind Thrust (SBT) (j) Sincar–Kerkük Blind Thrust Zone (SBTZ) (k) Adıyaman Thrust Zone (ATZ) (l) Raman Thrust Fault (RTF) and Garzan Thrust Fault (GTF) (m) Cizre Thrust Zone (CTZ) (n) Tectonic activity values of the faults E–W trending thrusts and NW–SE trending right-lateral and NE–SW trending left-lateral strike–slip faulting are active structures in the region 4.1 Major thrust-related earthquakes in E and SE Turkey In order to understand the internal structure of the SEAW, it would be useful to closely examine thrust-related earthquakes The first Van earthquake, which is located outside of SEAW, is reviewed; then the thrust-related Lice and Şırnak–Silopi earthquakes inside the SEAW will be examined 2011.10.23 (Mw: 7.1) Van earthquake Field reports (Akyüz et al., 2011; Emre et al., 2011; Erdik et al., 2012) and seismological reports (Zahrandik and Sokos, 2011) that followed the 2011.10.23 Van Earthquake confirm that the source of the earthquake is a north dipping thrust fault Some researchers conclude that the fault responsible for the 2011.10.23 Van earthquake (Mw: 7.1) is a blind fault, and related to this 116 surface deformations can be seen in the north of the city of Van (Özkaymak et al., 2011; Akyüz et al., 2011; Emre et al., 2011; Doğan and Karakaş, 2013) Although most observers agree on the source of the fault, which has been given different names (the Van Fault, the BardakỗSaray Thrust Fault, the Everek Reverse Fault), Koỗyiit (2013) is opposed to the blind fault evaluation and concludes that all major aftershocks were produced by separate individual faults in the region 1975.09.06 (Ms: 6.7) Lice earthquake Arpat (1977) presented detailed field observations and concluded that the 1975 Lice earthquake was related to reverse faulting, evidenced by the ground cracks (17–19 cm), left lateral displacements (13–14 cm), and the 60-cm up-throw of the surface along a distance of 300 m The deformations were mapped around the village of Yünlüce in the Miocene Lice Formation; this formation is the autochthonous unit in the footwall of a major thrust fault 16:32:51:0 37.75 16:44:11:0 37.80 1996/01/04 1996/01/11 1996/07/09 2000/11/15 2004/10/05 2005/01/25 10 2005/01/25 00:17:38:0 36.84 15:05:37.0 38.41 21:49:22.1 36.56 23:03:36.2 36.55 15:28:07.3 36.64 14:35:46.8 36.33 43.48 43.51 41.25 42.95 39.34 40.62 40.79 39.80 0.2 0.3 48 3.8 3.8 2.5 3.8 10 4.9 4.5 3.4 5.4 4.8 4.6 4.7 4.3 6.7 ML ML ML Ms ML ML ML ML Ms Ms 1995/04/22 40.72 6.5 45 45 Abdul-Wahed and Al-Tahhan 161 (2010) Abdul-Wahed and Al-Tahhan 146 (2010) This Study This Study This Study 125 60 307 90 85 81 64 50 Abdul-Wahed and Al-Tahhan 161 (2010) 100 45 Abdul-Wahed and Al-Tahhan 141 (2010) ISC 54 244 Jackson and McKenzie (1984) 64 304 KOERI -170 10 160 111 -170 -180 -175 -175 54 147 Dip1 Rake1 (°) (°) 09:20:11.0 38.47 26 Reference 1975/09/06 41.56 MTyp 12:22:10.5 39.17 Mag 1966/08/19 Depth (km) Lon (°E) Str1 (°) Lat (°N) Date (y/m/d) # Time (GMT) Fault plane parameters Earthquake parameters 35 329 40 239 51 71 66 46 114 50 Str2 (°) 80 80 70 33 85 90 85 85 50 61 Dip2 (°) Table Earthquake parameters and focal mechanism solutions of the major seismic events in the research area 175 10 54 -45 -45 -50 -50 128 30 Rake2 (°) 350 194 355 175 357 16 17 353 359 358 Pazm (°) 7 17 36 30 30 33 Pplg (°) 260 285 262 46 106 126 122 103 94 266 11 21 65 24 30 24 27 62 41 Tazm Tplg (°) (°) This Study This Study This Study Tan (2004) Abdul-Wahed and Al-Tahhan (2010) Abdul-Wahed and Al-Tahhan (2010) Abdul-Wahed and Al-Tahhan (2010) Abdul-Wahed and Al-Tahhan (2010) Jackson and McKenzie (1984) McKenzie (1972) Reference Beach Ball SEYİTOĞLU et al / Turkish J Earth Sci 117 118 17:11:02:0 37.92 17:15:13:0 38.01 17:52:13:0 37.93 00:04:51:0 38.60 11:16:19:0 37.74 12:22:28:0 37.61 15:11:52:0 37.69 01:23:27:0 37.75 13:05:14:0 37.76 21:41:03:0 36.98 02:56:00:0 37.65 11 2005/01/25 12 2005/01/25 13 2005/01/25 14 2005/01/26 15 2005/01/26 16 2005/01/26 17 2005/01/26 18 2005/01/27 19 2005/01/29 20 2005/05/29 21 2006/05/21 Table (Continued) 43.61 42.05 43.76 43.68 43.54 44.25 43.79 44.19 43.32 43.46 44.41 6.9 3.1 9.9 6.8 2.5 13.5 5.4 9.3 0.1 1.9 14 3.9 4.3 3.9 4.1 4 4.1 4.1 4.3 4.1 4.4 ML ML ML ML ML ML ML ML ML ML ML This Study This Study This Study This Study This Study This Study This Study This Study This Study This Study This Study 194 272 300 115 207 180 120 170 41 143 92 77 66 90 90 80 55 90 75 76 54 74 128 123 -15 10 165 -50 -155 45 164 127 -143 300 35 30 25 300 304 30 65 135 270 350 40 40 75 80 75 51 65 47 75 50 55 20 40 -180 180 10 -133 159 15 50 -20 256 339 254 250 254 149 348 292 88 207 316 23 14 11 58 17 17 37 142 226 346 340 163 243 252 38 358 113 217 44 56 11 18 17 42 21 60 12 This Study This Study This Study This Study This Study This Study This Study This Study This Study This Study This Study SEYİTOĞLU et al / Turkish J Earth Sci 10:21:24:0 37.58 08:12:36:0 37.28 22:50:53:0 37.67 09:08:57:0 37.27 23:19:57:0 37.17 20:53:22:0 36.18 13:13:02:0 37.26 10:41:21.0 38.779 43.351 15 03:17:04:0 38.4983 40.7248 5.4 25 2007/09/22 26 2007/09/24 27 2007/11/09 28 2008/05/11 29 2009/03/01 30 2009/03/10 31 2011/10/23 32 2012/04/28 43.56 42.32 43.32 44.38 43.84 42.93 43.97 3.7 5.4 8.7 3.6 16 0.6 24 2007/09/21 41.09 13:56:25:0 36.50 9.8 23 2006/11/16 42.6 03:48:34:0 37.91 22 2006/05/21 Table (Continued) 4.7 7.1 4.3 4.3 4.3 4.2 4.4 4.5 4.2 4.9 ML Mw ML ML ML ML ML ML ML ML ML 318 236 Zahradnik and Sokos (2011) This Study 164 129 145 190 104 191 255 136 200 This Study This Study This Study This Study This Study This Study This Study This Study This Study 69 46 86 85 90 55 76 60 80 85 85 131 70 -135 170 -155 -50 -164 145 -55 -170 -50 70 84 70 220 55 314 10 300 359 45 296 45 48 45 80 65 51 75 60 36 80 40 30 110 -5 -133 -15 35 -163 -5 -172 19 160 37 175 13 159 327 245 199 145 14 33 17 58 21 44 11 37 272 67 288 84 277 253 237 155 318 270 259 49 76 27 11 17 45 27 29 This Study Zahradnik and Sokos (2011) This Study This Study This Study This Study This Study This Study This Study This Study This Study SEYİTOĞLU et al / Turkish J Earth Sci 119 120 08:22:15:0 38.85 21:34:59:0 36.8215 42.2828 07:59:39:0 37.2875 38.644 35 2014/09/28 36 2014/12/23 37 2015/11/10 41.00 18.9 01:10:27:0 36.49 34 2013/08/02 43.48 05:52:51.0 37.1572 42.4437 11.68 33 2012/06/14 Table (Continued) 3.6 4.1 4.5 5.1 ML ML ML ML Mw This Study This Study This Study This Study AFAD 35 120 301 309 333 75 76 76 66 52 -40 159 164 108 141 137 215 35 90 90 52 70 75 30 60 -161 15 15 55 45 349 168 348 25 210 38 19 91 76 258 250 306 15 24 21 64 52 This Study This Study This Study This Study AFAD SEYİTOĞLU et al / Turkish J Earth Sci SEYİTOĞLU et al / Turkish J Earth Sci Figure 13 Earthquake activity of southeastern Turkey, northern Syria, and Iraq between 1900 and 2015 Earthquake epicenter data (purple dots) are provided by the Boaziỗi University Kandilli Observatory and Earthquake Research Institute (KOERI) Digital elevation model is obtained from the SRTM arc-second data Black lines are active structures outside of the SEAW Red solid lines with triangles on the hanging wall are thrust faults; dotted dashed lines represent the blind thrusts Normal faults are shown by a rectangle on the hanging wall Strike–slip faults are shown with half arrows Red focal mechanism solutions are from different sources (see Table for references) Black focal mechanism solutions are produced in this study See Table for details N-S cross section in which earthquake data inside the dotted area are plotted NAFZ: North Anatolian Fault Zone, EAFZ: East Anatolian Fault Zone, BZSZ: Bitlis–Zagros Suture Zone, XVIII: Van Thrust Fault, XIX: Bozova Fault, AG: AkỗakaleHarran Graben, XXI: emdinliYỹksekova Fault, XV: Bikhayr Blind Thrust Zone, XVI: Sincar–Kerkük Blind Thrust Zone representing the BZSZ (Arpat, 1977) The focal mechanism solution of the 1975.09.06 Lice earthquake indicates a 54° NW dipping fault surface at 10-km depth (Jackson and McKenzie, 1984) This requires a distant surface rupture around km south of the epicenter The reverse faults mapped by Arpat (1977) after the 1975 earthquake are only 600 m south of the epicenter For this reason, Arpat’s (1977) observations should be evaluated as surface deformations caused by the earthquake and they cannot be regarded as a major surface break of the earthquake produced by a regional thrust fault If the depth and dip of fault values (Jackson and McKenzie, 1984) are taken into account, the thrust fault responsible for the 1975 Lice earthquake should be traced at the surface south of the epicenter Interestingly, this location somewhat corresponds to the newly determined the Ergani–Silvan Blind Thrust Fault (in this paper) and this should then be evaluated as a possible source of the 1975.09.06 Lice earthquake (Figure 14a) 2012.06.14 (Mw: 5.1) Şırnak–Silopi earthquake According to the preliminary report by the Disaster and Emergency Management Presidency of Turkey (AFAD), the focal mechanism solution (based on P wave first motion) of the Şırnak–Silopi earthquake (2012.06.14; Mw: 5.1) indicates thrust faulting with a depth of 11.6 km (AFAD, 2012a) While the foreshock (2012.06.14–05:50) and main shock (2012.06.14–05:52) indicate thrusting, its aftershock (2012.06.15–23:48) has a strike–slip character (AFAD, 2012b) Neither the preliminary nor the monthly AFAD reports provide the name of the faults responsible for these seismic events The information about location, depth, and focal mechanism solutions suggests that the fault responsible for the Şırnak–Silopi earthquake is the Bikhayr Blind Thrust Fault (Figure 14b) Discussion Türkoğlu et al.’s (2008) magnetotelluric data point out a low resistivity area in the south of the BZSZ and the area’s thickness is reduced towards the south (Figures 121 SEYİTOĞLU et al / Turkish J Earth Sci Figure 14 (a) Relationship of the 1975.09.06 Lice Earthquake and the Ergani–Silvan Blind Thrust (EBT) (b) Relationship between the 2012.06.14 Cizre-Silopi Earthquake and the Bikhayr Blind Thrust Zone (BBTZ) BZSZ: Bitlis–Zagros Suture Zone, CTF: Cizre Thrust Fault, SBT: Silopi Blind Thrust 15a and 15b) A regional cross section made with seismic data indicates that the SEAW can be correlated with the magnetotelluric data (Figure 15c) After examining thrust-related earthquakes in the region, it can be seen that north dipping thrust surfaces have a range of dip angle of 46°–66° These values are very high for the basal thrust angle of a tectonic wedge when they are compared to the low surface angle value of the SEAW For this reason, it can be speculated that seismic activity occurs generally on the splays of faults separated from the basal thrust (Figure 15c) The other explanation for the absence of focal mechanism solutions showing low angle thrust fault surfaces is the probable ductile shearing on the basal thrust as suggested by Berberian (1995) for the Zagros foreland The seismic activity of the SEAW might be 122 triggered by both the northward movement of the Arabian plate (Aktuğ et al., 2016) and the surface uplift of eastern Anatolia due to asthenospheric cushioning (Şengör et al., 2008) obeying the critical taper model of Dahlen (1990) The nodal planes of the focal mechanism solutions obtained from the thrust-related earthquakes (i.e 1975.09.06 Lice and 2012.06.14 Şırnak–Silopi earthquakes) are parallel to the regional asymmetrical anticline axes at the surface This pattern is an indication of active blind thrust faults in the SEAW The general linear morphology between the asymmetric anticlines and Plio-Quaternary/ Quaternary deposits supports this argument The lack of detailed Quaternary stratigraphy and morphometric analyses in the region prevents any assignment about shortening and uplift rates across the SEAW SEYİTOĞLU et al / Turkish J Earth Sci Figure 15 (a) An enlarged magnetotelluric cross section by Türkoğlu et al (2008) indicating that low resistivity areas have a wedge shape (b) The regional MT cross section from Türkoğlu et al (2008) For location see Figure (c) The regional topographic cross section with earthquake hypocenter data (purple dots) indicating SEAW on the south of BZSZ Please note the surface slope that is identical with the ideal tectonic wedge shown in the Figure (d) The overall structure of east and southeast of Anatolia EAAC: East Anatolian Accretionary Complex (Şengör et al., 2008), BM: Bitlis Massif (Oberhansli et al., 2010), SEAW: Southeast Anatolian Wedge (this paper), BZSZ: Bitlis Zagros Suture Zone, XVII: Muş Thrust Fault, XII: Garzan Thrust Fault, XI: Raman Thrust Fault, XIII: Cizre Thrust Fault, IX: Mardin Blind Thrust Fault, XVI: Sincar–Kerkük Blind Thrust Zone The overall and simplified structure shown by the map view is composed of E–W trending thrusts and NW–SE right lateral and NE–SW left-lateral strike–slip faulting The seismicity in the region demonstrates that all of the structures mentioned above are active and working together The strike–slip faulting generally plays a role in tear faulting When releasing bend and releasing stepover structures are developed along the strike–slip system, the Karacada extensional fissure and AkỗakaleHarran graben locations fit these structures This is one of the important outcomes of the newly proposed neotectonic framework of the region that explains every major structure in the area, such as the position of the Sincar and Abdülaziz mountains uplifting in the Mesopotamian plain at the southern tip of the SEAW Conclusion In the north of the BZSZ, the East Anatolian Accretionary Complex has previously been determined (Şengör et al., 2003, 2008) After defining the SEAW in the south of the BZSZ with this paper, the overall structure of east and southeast Anatolia has emerged (Figure 15d) The internal structure of the SEAW is composed of several fault-propagation folds on the hanging wall of thrust/blind thrust faults, which is similar to the Zagros foreland, and their relationship with the Quaternary deposits has been demonstrated 123 SEYİTOĞLU et al / Turkish J Earth Sci This paper provides a new neotectonic framework for SE Turkey, northern Iraq, and Syria This represents a milestone in our developing understanding of the relationship between the active structures and seismic activity in the region, which was previously evaluated as a simple fold belt, and where the structures observed in these countries were not seen binding each other in the previous studies Until the 2011.10.23 Van earthquake (Mw: 7.1) the only known major thrust-related earthquake in the instrumental period was the 1975.09.06 Lice earthquake (Ms: 6.7), and earth scientists had a perception that the deformation in SE Anatolia mainly accommodated with strike–slip faulting The Van earthquake teaches us that blind thrusts are among the most important sources of major earthquakes in the region This paper demonstrates that the internal structure of the SEAW contains many thrusts/blind thrusts, some of which may be potential sources of future earthquakes, as suggested in the cases of the 1975.09.06 Lice and 2012.06.14 Şırnak–Silopi earthquakes Configuration of the fault lines in this paper should be further analyzed in the field and the active tectonic map of the region must be revised accordingly Acknowledgments The first author wishes to thank Mark Brandon for several discussions on the mechanism of the wedges during his sabbatical leave (2011–2012) at Yale University, where the main idea of this paper was propagated Fruitful discussions with Turkish Petroleum geologists Remzi Aksu, Nuray Şahbaz, and 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Figure Neotectonics of southeastern Turkey, northern Syria, and northern Iraq Digital elevation model is obtained from the SRTM arc-second data Black lines are active structures outside of the SEAW... (Figure 12k) Seismotectonics of southeastern Turkey, northern Syria, and Iraq The epicenter distribution of the earthquakes from the Boaziỗi University Kandilli Observatory and Earthquake Research