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Tectonics of the buried Kırklareli Fault, Thrace Region, NW Turkey
Quaternary International 312 (2013) 120e131
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Tectonics of the buried Kırklareli Fault, Thrace Region, NW Turkey H. Haluk Selim _ ı No. 4, Küçükyalı Kampusu, Istanbul Commerce University, Faculty of Engineering and Design, Department of Jewellery Engineering, Inönü Cd. E-5 Kavs¸ag Istanbul 34840, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history: Available online 1 June 2013
The study investigated the geometry, seismicity and kinematics of the Kırklareli Fault (KF) by using drilling, seismic reflection and field data. The KF, located in the Thrace Region, NW Turkey, is a buried fault that forms a morphological boundary between the Strandzha Mountains and the Ergene Basin. It has lithological and morphological importance in the region. Although there were some destructive earthquakes in the basin historically, the magnitude of the largest earthquake measured instrumentally was only 4.6. Earthquake data obtained from the Kandilli Observatory and Earthquake Research Institute indicate that the epicentres are concentrated along the KF. Deep borehole data show a total vertical displacement of 223 m over the last 2 Ma. Displacement calculations indicated that the KF moves with a normal displacement of at least 0.1 mm/year. The seismic profile verified the existence of the KF. Kinematic analysis of measurements on bedding planes of a formation near the KF demonstrates N105 direction. The activeness and existence of the hangingwall and footwall of the KF are discussed on the basis of morphometric analyses and geomorphic indices. The two geomorphic indices (SL and Vf) show that tectonism effects the morphology. The KF has normal fault geometry according to drilling, seismological and GPS data, geomorphic indices and field observations. Ó 2013 Elsevier Ltd and INQUA. All rights reserved.
1. Introduction The Thrace Region is located in northwest Turkey and in the southeast of the Balkan Peninsula. The region includes an elevated area (Strandzha Mountains) in northeast and a plain (Ergene Basin) in southwest. The study area is located between the elevated area and the plain (Fig. 1) approximately in the mid-section of the Thrace Region. The geometry, seismicity, and kinematics of the Kırklareli Fault (KF), extending NW-SE through the Strandzha Mountains and the Ergene Basin, were investigated in this study. The KF presents a lineament structure and is a buried fault that forms a morphological boundary between the Strandzha Mountains and the Ergene Basin. There are several studies discussing buried faults in Turkey and worldwide (Ekström et al., 1992; Liuan and Karakas¸, 2013; Karakas¸ et al., 2013). Zeng et al., 2009; Dog The KF has less tectonic activity than the faults of the North Anatolian Fault system. The two faults, North Osmancık Fault and Terzili Fault, are located south of the KF (see Fig. 1). Perinçek (1991), Turgut et al. (1991), and Görür and Okay (1996) studied the geometry and kinematics of the North Osmancık Fault and Terzili Fault. The Ergene Basin contains deposits with a 7 km thickness
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(Burchfiel et al., 2008a) and sedimentation continues in the basin. The Terzili and North Osmancık faults that control the Ergene Basin are buried active faults. The Terzili Fault has a negative flower structure and one of its segments is named the KF (Perinçek, 1991). The geometry of the KF supports the extensional system model recognized in the studies (Burchfiel et al., 2008a, 2008b) of the South Balkan Region. This extensional system is associated with the approximately NeS Aegean-Marmara extension regime. There is no detailed study about the KF, so the purpose of this study is to investigate the geometry, kinematics and seismicity of the KF in detail. The methods used to investigate the KF were the assessment of drilling data, analysis of seismic reflection profile, calculation of geometric indices, and detailed field observations. GPS data for the eastern Thrace Region (Deniz and Özener, 2010) were studied for evidence of fault activity. This paper applies a quantitative geomorphological method to the study area to evaluate relative rates of tectonic activity (Iat). Geomorphic Indices (GIs), such as drainage basin river lengthri and S¸eytan streams) gradient index (SL index) (for the Teke, I_g and ratio of valley floor width to valley height (Vf index, for the _ Teke, Inci and S¸eytan streams) were determined to understand the morphological evolution of the study area (Hack, 1973; Keller and Pinter, 1996; Selim et al., 2013). Finally, the morphotectonic origin of the drainage systems influenced by the KF is discussed.
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Fig. 1. Morpho-tectonic map of the investigation area and the Strandzha Mountains, Terzili strike-slip Fault and North Osmancık normal Fault are defined by Perinçek (1991), Turgut et al. (1991), Görür and Okay (1996) and Kırklareli normal Fault. (þ; Footwall, e; Hanging wall).
2. Geological setting The geology of the Thrace Region has been investigated by numerous researchers. Paeckelmann (1938) defined the age of the rocks based on the paleontological data in the region. Akartuna (1953) stated that the Neogene units consisted of Miocene and Pliocene sequences. Öztunalı and Üs¸ümezsoy (1979) put forth the petrographic features of the core complex of the Strandzha Massif. layan (1996) indicated that opening of the Ergene Basin started Çag in the Jurassic due to an extensional regime, and sediment deposition continued transgressively north during the Late Eocenelayan and Yurtsever (1998) mapped the geological Neogene. Çag setting of the region in detail. Sakınç et al. (1999) defined the age of Ergene Formation as Late Miocene-Pliocene. Okay et al. (2001) noted that the Strandzha Massif was developed as an intra-arc basin in the Senonian and changed to a magmatic arc due to the north-dipping Tethys oceanic lithosphere. Kaymakçı et al. (2007) determined the age of the alkaline volcanic rocks as 4 Ma (Late Miocene) based on 40Ar/39Ar dating. The stratigraphy of the study area is generally divided into two units. The basement unit is composed of metamorphic rocks (Strandzha Massif). The overlying unit is composed of Paleogene and Neogene sediments. The lithologies of the Strandzha Massif were covered by the sediments of the Ergene Basin. The oldest unit of the Strandzha Massif is the Tekedere Group, which consists of schist, pegmatite and gneiss and S¸eytandere metagranite with orthoclase and microcline. The group is exposed in small areas along both sides of the Teke Stream valley and both sides of the S¸eytan Stream valley. The S¸eytandere metagranite shows prominent steep-slope morphology. Isotopic dating using the single zircon PbePb evaporation method shows that there are two magmatic events: one occurred within a short time interval between 312 2 and 315 5 Ma and the other one is dated as 257 6 Ma (Sunal et al., 2008). According to Okay et al. (2008), the Pontides also consist of three terranes: the Strandzha terrane has a Variscan basement, with Carboniferous, Permian granitoids and an epicontinental Triassic to Jurassic sedimentary cover. The units overlying the basement unconformably, from bottom ucak to top, are the Eocene Koyunbaba Formation, the Eocene Sog Formation (Özcan et al., 2010), the Eocene-Oligocene Pınarhisar
lu Formation, and Late MioceneFormation, the Oligocene Sülog Pliocene Ergene Formation (Sakınç et al., 1999). The Eocene Koyunbaba Formation, deposited unconformably on the metamorphic basement, is composed of a sequence of pebblestone, sandstone, limestone, and basal conglomerate. To the west of the ucak ForKırklareli Fault, it is concordantly overlain by the Sog aralar Hill. Formation outcrops mation and is exposed only in Mag are observed east, north and west of Kırklareli city. There are ucak Formation due to its friable lilimited outcrops of the Sog ucak Formation is a reef complex that consists of thology. The Sog cream-white limestone with beds of 1 m thickness or more. It is located in the footwall of the KF in the western part of the study area. The formation has outcrops on both the east and the west sides of the S¸eytan Stream valley, with 40 e50 dip slips on the bedding planes between the S¸eytan Stream valley and west of Kırklareli city. The Eocene-Oligocene Pınarhisar Formation conlayan and Yurtsever, tains limestone, sandstone and marl (Çag 1998). The formation is observed in the hanging wall of the fault, based on the drilling data. The Pınarhisar Formation overlies ucak Formation unconformably. The sandstone and quartz the Sog pebbles observed at the bottom of the formation indicate that these materials were derived from the margin of the Strandzha Massif. Deposition took place in a back reef lagoon facies. The relation of the formation with the reef is intertonguing in some locations and unconformable in others, based on the post-Eocene regression seen over the entire study area. The Upper Oligocene lu Formation is comprised of grey-yellow claystone, siltstone Sülog layan and Yurtsever, 1998). The unit is located and sandstone (Çag ucak Formation and extends to the unconformably on the Sog S¸eytan Stream valley in the east. The dip-slip measurements of the unit to the north of the KF are 25 on the footwall and 30 e40 on the hanging wall in the south of the fault. The youngest Neogene unit in the study area is the Late Miocene-Pliocene Ergene Formation. The unit consists of yellow, dark yellow and yellow-grey pebbles, coarse pebbles, and semi-cemented pebblestone, sandlu stone, and claystone. The Ergene Formation overlies the Sülog Formation unconformably. The KF contacts not only the Ergene ucak formations but also Sog ucak and Sülog lu formations and Sog in the study area (Fig. 2). These formations are covered unconformably by Quaternary alluvium (Fig. 3).
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Fig. 2. Geological map of the investigated area.
3. Field study and data analysis
SL ¼ ðDH=DLÞ L
The morphology of the study area is a highland in north and a depression in south. Morphologically, the Kırklareli Fault forms a boundary between the highland and depression area. The uplift consists of basement rocks and Eocene units, and the depression area consists of the Oligocene and Pliocene units. Morphological indications of the KF can be observed to the north of Koyunbaba ucak Village. It forms the morphological boundary between the Sog and Ergene formations. In the eastern part of the study area, the lu and fault forms the morphological boundary between the Sülog ucak formations, and between the Sülog lu and Koyunbaba Sog formations. The KF morphology linearly extends approximately N105 in the Thrace Region. This lineament controls the morphological and lithological boundaries. A plateau surface cut by deep valleys exists to the northeast of the Kırklareli Fault. In contrast, the topography in the north of the fault has lower relief than the south of the fault. According to the field observations, the Strandzha Mountains and valleys were shaped by the courses of the rivers. Valleys are narrow and deep north of the fault, but wide and shallow south of the fault. The average altitude north of the fault is around 200e240 m, and it is between 150 and 190 m to the south. Hack (1973) suggested the river length-gradient index (SL) to determine whether a river would be in geomorphologic equilibrium, based on the relationship between the river slope and the areal extent of the watershed (Eq. (1)). High SL values indicate deviations in cross-sectional stream profiles from their idealized, equilibrium form, which may be indicative of active and/or recent tectonic activity in an area.
(SL): river length-gradient index, (DH): elevation difference of the river, (DL): length of the river and (L): distance between the valley and peak. The first calculation of the GIs was performed for the study area and Teke Stream. The SL index of the Teke Stream has a high anomaly value peak around the fault from 25 to 208 (see Fig. 4A and Table 1) and the stream is in the class 1 category. In addition, the SL ri Stream shows a moderate anomaly value across the index of the I_g fault from 71 to 113 (see Fig. 4B and Table 1) and the river is in the class 2 category. Finally, the SL index of the S¸eytan Stream shows a low anomaly value across the fault from 43 to 90 (see Fig. 4C and Table 1) and the river is in the class 3 category.
(1)
Table 1 Values of the SL (river length-gradient index) for the study area streams (DH: elevation difference of the river, DL: length of the river and L: distance between the valley and peak). Streams/creeks
Low value
High value
SL anomaly
SL class
Teke ri I_g S¸eytan
25 71 43
208 113 90
High Moderate Low
1 2 3
Ratio of valley-floor width to valley height index (Vf) explains the effects of the tectonism on the profiles of the valley slopes (Eq. (2)). High Vf values indicate low uplift rates, while low Vf values indicate high uplift rates and deeply eroded valleys controlled by
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Fig. 3. Generalized stratigraphy of the investigation area.
tectonics. Thus, the relation between deep erosion and tectonics could be evaluated (Bull, 1977, 1978; Bull and McFadden, 1977; Keller and Pinter, 1996).
Vf ¼ 2:Vfw=ðEld EscÞ þ ðErd EscÞ
(2)
(Vf): ratio of valley-floor widthevalley height, (Vfw): valley-floor width, (Eld): elevation of the left valley divide, (Erd): elevation of the right valley divide and (Esc): elevation of the valley floor. According to the analyses performed along the cross-valley profiles, the Vf values were calculated to be 0.48 for the footwall and 14.12 for the hanging wall of the segment of A in the Teke
Stream valley. The Vf class for Teke Stream valley is defined as 2 (moderate). These values were obtained from the profiles 1 (Vf ¼ 0.48) and 2 (Vf ¼ 14.12) shown in Fig. 5 and Table 2. In addition, the Vf values were calculated to be 2 for the footwall and _ 82 for the hanging wall of the segment of B in the Inci Stream Valley. These values were obtained from the profiles 3 (Vf ¼ 2) and 4 _ (Vf ¼ 82) shown in Fig. 5 and Table 2. The Vf class for Inci Stream Valley is defined 1 (high). Finally, the Vf values were calculated to be 0.36 for the footwall and 9.17 for the hanging wall of the segment of C in the S¸eytan Stream Valley. These values were obtained from the profiles 5 (Vf ¼ 0.36) and 6 (Vf ¼ 9.17) shown in Fig. 5 and Table 2. The Vf class for S¸eytan Stream Valley is defined as 3 (Low).
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Table 2 Values of the Vf (ratio of valley floor width to valley height) for the study area valleys (Vfw: valley-floor width, Eld: elevation of the left valley divide, Erd: elevation of the right valley divide and Esc: elevation of the valley floor). Segments
Valleys
Hangingwall values
Footwall values
Vf class
A B C
Teke _ Inci S¸eytan
14.12 82 9.17
0.48 2 0.36
2 (Moderate) 1 (High) 3 (Low)
lu The hanging wall of the KF includes the Ergene and Sülog formations. The dip-slip measurements obtained on the beds of the Ergene Formation vary between 7 and 10 . The slopes of Ergene Formation change from 40 to 50 in locations near the KF. During the Oligocene-Miocene, the compression ended with moderate folding and faulting, best observed in the Thrace Region (Schindler, 1997). The folds are oriented E-W and NE-SW in the southern part of the study area. In addition, the folds might have developed in accordance with the KF and the other two faults. 4. Fault tectonics The tectonic setting of the Thrace region is controlled by two active tectonic plates: the Anatolian Plate and Eurasia Plate. The
Anatolian Plate rotates counter-clockwise according to previous GPS and tectonic studies, while the Eurasia Plate rotates clockwise (Westaway, 1994; Reilinger et al., 1997; Straub et al., 1997; Armijo et al., 1999; Barka et al., 2000; McClusky et al., 2000; Le Pichon et al., 2003). Additionally, Burchfiel et al. (2008a) state that there is extensional tectonism in east Macedonia, west Bulgaria, north Greece, and northwest Turkey (Thrace Region). Burchfiel et al. (2008b) state that this extension started in Mid-Miocene and is a part of the Aegean extensional system. Deniz and Özener (2010) recognized extensional tectonics through GPS studies in the Thrace Region (Fig. 6). There are several active and inactive faults in the region. The Terzili and North Osmancık faults (Perinçek, 1991; Turgut et al., 1991; Görür and Okay, 1996) are buried faults that have been detected by seismic investigations. The Kırklareli Fault is also a buried fault that forms a morphological boundary between the Strandzha Mountains in the north and the Ergene Basin in the south, a segment of the Terzili and Osmancık fault system. The KF affects the northern border of the Ergene Basin along the Strandzha Mountains and also forms the base of the Strandzha Massif. South of the Strandzha Massif, discontinuity detected by geophysical studies (Bayrak et al., 2004, 2006) is a normal fault exposing a linear structure that continues to the west of Istanbul. The buried KF was detected by drilling and geophysical studies (Perinçek, 1991; Turgut et al., 1991).
ri Stream c) S¸eytan Stream. Fig. 4. Longitudinal river profiles and SL values for a) Teke Stream b) I_g
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Fig. 5. Vf values and cross-valley profiles.
4.1. Seismology The seismicity of the Thrace Region depends on the active faults, including the Kırklareli Fault. A number of major earthquakes in the region occurred in 926e927 (Guidoboni, 1994), and in 1542, 1689, 1752, and 1802 AD (Ambraseys and Finkel, 1991). The 926e927 earthquake completely destroyed many towns and churches, with several ruptures seen on the ground. Several deaths resulted from the June 12th, 1542, earthquake which was felt in Istanbul, Gallipoli, and Edirne. The same earthquake destroyed 1700 houses in Istanbul. The April 25th, 1689 earthquake affected mainly northwest Anatolia, Thrace, and the western coasts of the Black Sea. Many houses, mosques, and churches in Istanbul and Edirne were damaged and the earthquake was felt in Sofia, Bulgaria. The estimated epicenter of this earthquake was in the Maritsa (Meriç) Valley. The July 29th, 1752 earthquake affected primarily the Thrace _ Region. Ibrik Hill, Havsa, and Hasköy were completely destroyed. Many houses and government buildings in Edirne were damaged and also many deaths recorded. Some collapses were noted within the Edirne city walls and the Edirne Castle. The earthquake was felt in Istanbul and Izmir. The October 26th, 1802 earthquake damaged
many houses, marketplaces, mosques and churches in Istanbul and Edirne. Seismic activity attributed to the Ergene Basin has been recorded instrumentally in the region in the 20th century. Several earthquakes (5 M 3) (Fig. 7) are clustered west and east of the KF. The clustering of the earthquakes is due to the lineament structure of the KF aligned approximately east-west. The most important earthquakes were in 1929 (M ¼ 4.5), 1967 (M ¼ 4.4), 1976 (M ¼ 3.7) and 1982 (M ¼ 4.6) according to the Kandilli Observatory earthquake data in the basin. Seismicity of the Ergene Basin is emphasized by a recent study (Horasan et al., 2009). The epicentres of these earthquakes (M 3) concentrated in the basin (around Kırklareli city) (Fig. 7) indicate that the seismic activity still continues. 4.2. Slip rate and geometry Four deep investigation boreholes drilled by the Kırklareli Municipality and DSI (General Directorate of State Hydraulic Works) were used to determine slip rate and geometry of the KF. Boreholes in the area were drilled on the hanging wall of the fault. The
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Fig. 6. GPS data between 2000 and 2006 in the Thrace Region and east Marmara (Deniz and Özener, 2010).
borehole logs of SDK-1 (drill log-1), SDK-2, SDK-3 and SDK-4 wells contain fault traces (Fig. 8). The SDK-1 and SDK-2 wells are the nearest boreholes to the fault and were drilled approximately 1800 m north of Koyunbaba village (see Figs. 2 and 9). The drilled wells were aligned into the same direction with the fault, approximately 100 m far from the fault trace (see Fig. 9). The depth of SDK1 well is 146 m. The first 140 m of this well includes the Ergene Formation, which is accepted as a reference for the bottom level, and the last 6 m is magmatic rock. The magmatic rocks are intrusive, rising through the Kırklareli Fault. The depth of the SDK-2 well is 225 m, with 200 m through the ucak ForErgene Formation and the remainder through the Sog mation. Similarly, the Ergene Formation was cut in the upper levels of the SDK-3 well drilled in the south. The Süloglu Formation is located between 30 m and 130 m depth in the SDK-3 well. The
Pınarhisar Formation continues from 130 m to 321 m. At the bottom of the SDK-3 well, there is a 1 m clay layer and the lower 2 m is granite. These data allow the KF to be defined as a normal fault with a 64 southward inclination. The inclination angle is calculated by the thickness (T) measured as 223 m and distance (D) to the fault plane measured as 110 m in Fig. 9. Thus, the inclination angle is calculated as approximately 64 by using equation (3).
a ¼ arctangðT=DÞ a ¼ arctangð223=110Þ ¼ 63; 74 ¼ w64
(3)
The minimum vertical displacement on the KF calculated with borehole data from the SDK-2 well is about 223 m. The fault is younger than the Pliocene deposits because it cuts through the Late
Fig. 7. Kırklareli Fault and earthquake epicenters (5 > M > 3) in the Thrace Region (Seismic data from the Kandilli Observatory and Earthquake Research Institute database, 2010).
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ucak and Ergene The KF forms the boundary between the Sog formations in the west. The dip of beds on the footwall in the upper ucak Formation is between 21 and 28 SE. However, levels of the Sog beds near the fault are tilted at 45 e50 . The part of the Ergene Formation forming the hanging wall of the fault is the youngest unit in the Ergene Basin, and is generally horizontal. Near the fault, the beds of the formation are backtilted 50 to the northeast in the ri Stream Valley (Fig. 10). Additionally, seismic studies conducted I_g in the area by the Turkish Petroleum Corporation (TPAO) clearly indicated that the Kırklareli Fault is a normal fault (Fig. 11). The seismic reflection data described by Turgut et al. (1991) reveal that the branches of the fault extend towards to the north, and the northernmost branch almost reaches the surface. The extension of the KF could be defined by a lineament in the morphology during the field observations. The KF can be divided into three segments (A, B and C) in the study area based on the morphological evidence. The first segment ucak is located north of Koyunbaba between the Ergene and Sog formations, oriented N105 e110 south of Kayalı and Eriklice (A). The second fault lineament is oriented about N115 e120 in lu and Sog ucak formations (B). Kırklareli city, between the Sülog The last segment of the KF extends approximately N90 east of ucak formations (C). Kırklareli city between the Ergene and Sog ucak Kinematic analysis of the measurements taken from the Sog Formation bedding planes, near the KF, shows a N30o-35 extension (Fig. 12). The paleostress directions calculated for segment A are 238.9 /54.8 for s1, 128.8 /13.9 for s2, and 29.8 /31.4 for s3; for segment B 276.5 /64.3 for s1, 148.4 /15.5 for s2, and 52.9 / 19.7 for s3; and for segment C 215 /41 for s1, 113 /8.3 for s2, and 17.1 /37.4 for s3 (c.f. Turner, 1953). The KF illustrated on Fig. 13 represents normal fault geometry in the study area based on morphological, geological, seismological and borehole data. In addition, the Kırklareli and North Osmancık faults converge at approximately 3 km depth according to seismic reflection data (Turgut et al., 1991; Gürgey, 2009). Fig. 8. Borehole logs, shown in Figs. 1 and 2, used to define the fault (Tas¸, 2002).
Miocene-Pliocene (Ergene Formation). If the offset (O) is taken as 223,000 mm and time (t) is taken as 2 Ma, the displacement rate is calculated as approximately 0.1 mm per year based on Equation (4).
O ¼ Vt 223000 mm ¼ V 2000000 yr
(4)
V (Velocity) ¼ 0.11 ¼ w0.1 mm/y (see Fig. 9)
Fig. 9. SDK-2 borehole data drilled near the fault plane of the Kırklareli Fault. At this point, KF is defined as a normal fault inclined 64 southward.
5. Discussion The KF has an important role in the tectonic model of the Thrace Region. The recent low magnitude earthquakes around Kırklareli city indicate seismic activity of the fault. The geometry of fault described in the study is compatible with the tectonic model of the Ergene Basin of Perinçek (1991), Turgut et al. (1991), Sakınç et al. (1999), Yaltırak (2002), and Kaymakçı et al. (2007). The Kırklareli Fault is a buried fault, which backtilted the units of the Ergene Formation in the basin. While the beds of the Ergene
ri Stream Valley. Fig. 10. Ergene Formation view of backtilting to the northeast in the I_g
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Fig. 11. Structure of the Kırklareli Fault based on two-travel time seismic reflection data (Modified from Turgut et al., 1991).
Formation in the middle of the basin are approximately level, they are inclined 50 NE near the Strandzha Massif. The KF was defined in seismic profiles and oil exploration investigations (Gürgey et al., 2005; Gürgey, 2009), and in the drilling explorations carried out by
TPAO (Turgut et al., 1991). The fault is an indistinct morphological lineament on the surface and probably is the contact between the Strandzha Massif and Ergene Basin. However, the fault plane is unobservable south of the massif. The dip-slip measurements taken ucak Formation are parallel to the fault plane of the from the Sog footwall. The movement of the fault is quite low (w0.1 mm/y). This situation restricts the geological evidence of the fault in the field. Although the KF shows only morphological evidence in the field, it almost reaches the surface in the seismic section (Perinçek, 1991; Turgut et al., 1991; Gürgey et al., 2005; Gürgey, 2009). The fault plane is encountered at 223 m depth of the SDK-2 well in Fig. 9, and the granite intrusive cut in the SDK-1 well (see Fig. 8) is an indication of the KF. The faults located in the Ergene Basin were defined in the previous studies of Perinçek (1991), Turgut et al. (1991), Görür and Okay (1996), Kaymakçı et al. (2007), and Yaltırak (2002). The faults displayed in Fig. 13 indicate that the Terzili Fault is the main fault, and the North Osmancık and Kırklareli faults are the branches of the Terzili Fault in the basin. The Kırklareli Fault is the closest branch of the Terzili and North Osmancık faults to the surface. All of the faults located in the Ergene Basin are buried faults, and the KF investigated by this study should be considered as a part of this fault system. The tectonic studies related to the northwest of the Thrace Region indicate that there is an extensional tectonic regime, starting
ucak Formation near the Kırklareli Fault. Stereogram shows that extension occurred along approxiFig. 12. Kinematical analysis of measurements on bedding planes of the Sog mately N30o-35 orientation, measurements on bedding determined lower hemisphere. Equal-area projections of normal faults and stress directions computed using the PeT method (Turner, 1953). Great circle represents bedding plane; cross represent relative movement of the footwall.
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Fig. 13. Model of tectonic structure of the Ergene Basin between Kırklareli Fault, Terzili strike-slip Fault and North Osmancık normal Fault defined by Perinçek (1991) and Turgut et al. (1991).
in the Middle-Miocene. This extensional tectonism affecting east Macedonia, west Bulgaria, north Greece and northwest Turkey (Thrace Region) is possibly related to the Aegean extensional system (Burchfiel et al., 2008a, 2008b). The KF has developed as a result of this extensional regime as a normal fault. GPS studies undertaken in the region indicated that there is movement towards the northeast (Deniz and Özener, 2010). Kaymakçı et al. (2007) notes that the Thrace Region rotates clockwise, which creates an NE-SW extension and a fault zone (Thrace Fault Zone) related to the extension. This extensional tectonic regime supports the fault kinematics presented in this study. Instrumentally, several low and moderate magnitude earthquakes occurred in the basin. The
movement rate and activity of the fault are quite low compared to the North Anatolian Fault Zone. The relation between the tectonic effects of the KF and morphology was evaluated by relative tectonic activity index (Iat) to verify the presence of the fault. The Iat values were calculated based on the GIs (Table 3). The SL and Vf values obtained in this study were compared with the values given in Bull and McFadden (1977). The values of the Iat were divided into two classes to determine the degree of active tectonics: class 1 (high relative tectonic activity) and class 2 (moderate relative tectonic activity) (Fig. 14). The values obtained through the GIs and the Iat index grades indicate that the activity of the fault is higher in segments A and B than in segment C. The SL index values reach maximum in the areas affected by segment A. The SL values are high in Teke Stream, _ moderate in Inci Stream, and low in S¸eytan Stream. Calculated SL values shown in Fig. 4C indicate that several synthetic faults parallel to the KF should be present. Vf values of the hanging walls are higher that the Vf values of the footwalls, confirmingthe existence of the KF. The buried Kırklareli Fault, capable of producing earthquakes, is located in the northernmost fault system in the basin and is a branch of the North Osmancık normal Fault. Table 3 Iat classification of areas located in front of each segment.
Fig. 14. Classification of the Iat (relative tectonic activity index) in the basin of the study area (SL: river length-gradient index, Vf: ratio of valley floor width to valley height and S/n: total values of classes/number of classes).
Segments of the KF
Streams/ creeks
SL indices
Vf indices
Time Ma
Geological velocity
S/n
Iat class
A A B C
Teke ri I_g _ Inci
1 2 e 3
2 e 1 3
2 2 2 2
0.1 0.1 0.1 0.1
1.5 1 1 3
1 1 1 2
S¸eytan
mm/y mm/y mm/y mm/y
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6. Conclusions This study analysed the tectonic presence of the KF and its effects on the geomorphology of the study area by using the tectonic evidence, GIs, seismology, drilling and seismic reflection data, and field observations. The Kırklareli Fault is located in the northernmost part of the Ergene Basin. In the northwestern part of the study ucak forarea, the fault is the contact between the Ergene and Sog mations. The KF can be divided into three segments (A, B and C) in the study area based on the morphological evidence. The KF is oriented N105 -110 around the south of Kayalı and Eriklice villages, and Kırklareli city. The fault is a part of the morphological lineament extending NW-SE between the Strandzha Mountains and Ergene Basin. Kinematic analysis of measurements on bedding ucak Formation, near the Kırklareli planes, obtained from the Sog normal Fault indicates that the extension is approximately N30 35 . Recorded seismic activity in the region during the 20th century indicates that the faults are active in this region with a maximum recorded magnitude of 4.6. The GPS data indicate northeast movement. Historical earthquakes between 926 and 1802 A.D. caused significant destruction. According to data from wells drilled near to the fault, minimum vertical slip of the Kırklareli Fault is 223 m, and the slip rate is a minimum 0.1 mm/yr. The morphotectonics of the KF were defined by calculating the GIs. The values obtained through the GIs and the Iat index grades supported the existence of the KF in the study area. Segments A and B are rated as class 1 with high tectonic activity, and segment C is defined as class 2, with has moderate tectonic activity. The Vf and SL index values are consistent for the Teke and S¸eytan streams and verify the tectonic effect of the KF on morphology. Field observations and data, the GIs, and velocity calculations support the morphotectonic evidence on the Kırklareli Fault.
Acknowledgements We would like to thank Dr. Ahmet Karakas¸ (Kocaeli University) and K. Ömer Tas¸ (Sakarya University) for their helpful discussion and critical reading. We are also indebted to Dr. Onur Tan (TübitakMarmara Research Centre) for the digital maps and Muzaffer Siyako (Turkish Petroleum Corporation-TPAO) for data support.
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Engineering geologic assessment of the slope Karakas¸, A., Coruk, Ö., Dog movements and liquefaction failures of the 23 October 2011 Van earthquake (Mw ¼ 7.2). Natural Hazards and Earth System Sciences 13, 1113e1126. Kaymakçı, N., Aldanmaz, E., Langereis, C., Spell, T.L., Gürer, Ö.F., Zanetti, K.A., 2007. Late Miocene transcurrent tectonics in NW Turkey: evidence from palaeomagnetism and 40Ar-39 dating of alkaline volcanic rocks. Geological Magazine 144 (2), 379e392. Keller, E.A., Pinter, N., 1996. Active Tectonics: Earthquakes Uplift and Landscape. Prentice Hall, New Jersey. Le Pichon, X., Chamot-Rooke, N., Rangin, C., S¸engör, A.M.C., 2003. The north Anatolian fault in the Sea of Marmara. Journal of Geophysical Research 108, 1e20. Liu-Zeng, J., Zhang, Z., Wen, L., Tapponnier, P., Sun, J., Xing, X., Hu, G., Xu, Q., Zeng, L., Ding, L., Ji, C., Hudnut, K.W., van der Woerd, J., 2009. Co-seismic ruptures of the 12 May 2008, Ms ¼ 8.0 Wenchuan Earthquake, Sichuan: east-west crustal shortening on oblique, parallel thrusts along the eastern edge of Tibet. Earth and Planetary Science Letters 286, 355e370. McClusky, S., Balassanian, S., Barka, A.A., Demir, C., Ergintav, S., Georgiev, I., Gürkan, O., Hamburger, M., Hurst, K., Kahle, H., Kastens, K., Kekelidze, G., Kotzev, V., Lenk, O., Mahmoud, S., Mishin, A., Nadariya, M., Ouzounis, A., Paradissis, D., Peter, Y., Prilepin, M., Reilinger, R., S¸anlı, I., Seeger, H., Tealeb, A., Toksöz, H.N., Veis, G., 2000. Global positioning system constraints on the plate kinematics in the eastern Mediterranean and Caucasus. Journal of Geophysical Research 105, 5695e5719. Okay, A.I., Satır, M., Tüysüz, O., Akyüz, S., Chen, F., 2001. The tectonics of the Strandzha Massif: Late-Variscan and Mid-Mesozoic deformation and metamorphism in the northern Aegean. International Journal of Earth Sciences 90, 217e233. itbas¸, E., Crowley, Q.G., Shang, C.K., 2008. Okay, A.I., Bozkurt, E., Satır, M., Yig Defining the southern margin of Avalonia in the Pontides: geochronological data from the Late Proterozoic and Ordovician granitoids from NW Turkey. Tectonophysics 461 (1e4), 252e264. Öztunalı, Ö., Üs¸ümezsoy, S., 1979. Core complex rocks of the Strandzha Massive and its petrogenetic evolution. In: Altınlı Symposium, pp. 37e44. Ankara. Özcan, E., Less, G., Okay, A.I., Baldi-Beke, M., Kollanyi, K., Yılmaz, I.Ö., 2010. Stratigraphy and Larger Foraminifera of the Eocene Shallow-marine and Olistostromal Units of the southern part of the Thrace Basin, NW Turkey. Turkish Journal of Earth Sciences 19, 27e77. Paeckelmann, W., 1938. Neue beitrage zur Kenntnis der Geologie, Paläontologie und Petrographie, der umgebend von Konstantinopel. In: 2. 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Tectonics of the buried Kırklareli Fault, Thrace Region, NW Turkey H. Haluk Selim _ ı No. 4, Küçükyalı Kampusu, Istanbul Commerce University, Faculty of Engineering and Design, Department of Jewellery Engineering, Inönü Cd. E-5 Kavs¸ag Istanbul 34840, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history: Available online 1 June 2013
The study investigated the geometry, seismicity and kinematics of the Kırklareli Fault (KF) by using drilling, seismic reflection and field data. The KF, located in the Thrace Region, NW Turkey, is a buried fault that forms a morphological boundary between the Strandzha Mountains and the Ergene Basin. It has lithological and morphological importance in the region. Although there were some destructive earthquakes in the basin historically, the magnitude of the largest earthquake measured instrumentally was only 4.6. Earthquake data obtained from the Kandilli Observatory and Earthquake Research Institute indicate that the epicentres are concentrated along the KF. Deep borehole data show a total vertical displacement of 223 m over the last 2 Ma. Displacement calculations indicated that the KF moves with a normal displacement of at least 0.1 mm/year. The seismic profile verified the existence of the KF. Kinematic analysis of measurements on bedding planes of a formation near the KF demonstrates N105 direction. The activeness and existence of the hangingwall and footwall of the KF are discussed on the basis of morphometric analyses and geomorphic indices. The two geomorphic indices (SL and Vf) show that tectonism effects the morphology. The KF has normal fault geometry according to drilling, seismological and GPS data, geomorphic indices and field observations. Ó 2013 Elsevier Ltd and INQUA. All rights reserved.
1. Introduction The Thrace Region is located in northwest Turkey and in the southeast of the Balkan Peninsula. The region includes an elevated area (Strandzha Mountains) in northeast and a plain (Ergene Basin) in southwest. The study area is located between the elevated area and the plain (Fig. 1) approximately in the mid-section of the Thrace Region. The geometry, seismicity, and kinematics of the Kırklareli Fault (KF), extending NW-SE through the Strandzha Mountains and the Ergene Basin, were investigated in this study. The KF presents a lineament structure and is a buried fault that forms a morphological boundary between the Strandzha Mountains and the Ergene Basin. There are several studies discussing buried faults in Turkey and worldwide (Ekström et al., 1992; Liuan and Karakas¸, 2013; Karakas¸ et al., 2013). Zeng et al., 2009; Dog The KF has less tectonic activity than the faults of the North Anatolian Fault system. The two faults, North Osmancık Fault and Terzili Fault, are located south of the KF (see Fig. 1). Perinçek (1991), Turgut et al. (1991), and Görür and Okay (1996) studied the geometry and kinematics of the North Osmancık Fault and Terzili Fault. The Ergene Basin contains deposits with a 7 km thickness
E-mail addresses: [email protected], [email protected]. 1040-6182/$ e see front matter Ó 2013 Elsevier Ltd and INQUA. All rights reserved. http://dx.doi.org/10.1016/j.quaint.2013.05.040
(Burchfiel et al., 2008a) and sedimentation continues in the basin. The Terzili and North Osmancık faults that control the Ergene Basin are buried active faults. The Terzili Fault has a negative flower structure and one of its segments is named the KF (Perinçek, 1991). The geometry of the KF supports the extensional system model recognized in the studies (Burchfiel et al., 2008a, 2008b) of the South Balkan Region. This extensional system is associated with the approximately NeS Aegean-Marmara extension regime. There is no detailed study about the KF, so the purpose of this study is to investigate the geometry, kinematics and seismicity of the KF in detail. The methods used to investigate the KF were the assessment of drilling data, analysis of seismic reflection profile, calculation of geometric indices, and detailed field observations. GPS data for the eastern Thrace Region (Deniz and Özener, 2010) were studied for evidence of fault activity. This paper applies a quantitative geomorphological method to the study area to evaluate relative rates of tectonic activity (Iat). Geomorphic Indices (GIs), such as drainage basin river lengthri and S¸eytan streams) gradient index (SL index) (for the Teke, I_g and ratio of valley floor width to valley height (Vf index, for the _ Teke, Inci and S¸eytan streams) were determined to understand the morphological evolution of the study area (Hack, 1973; Keller and Pinter, 1996; Selim et al., 2013). Finally, the morphotectonic origin of the drainage systems influenced by the KF is discussed.
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Fig. 1. Morpho-tectonic map of the investigation area and the Strandzha Mountains, Terzili strike-slip Fault and North Osmancık normal Fault are defined by Perinçek (1991), Turgut et al. (1991), Görür and Okay (1996) and Kırklareli normal Fault. (þ; Footwall, e; Hanging wall).
2. Geological setting The geology of the Thrace Region has been investigated by numerous researchers. Paeckelmann (1938) defined the age of the rocks based on the paleontological data in the region. Akartuna (1953) stated that the Neogene units consisted of Miocene and Pliocene sequences. Öztunalı and Üs¸ümezsoy (1979) put forth the petrographic features of the core complex of the Strandzha Massif. layan (1996) indicated that opening of the Ergene Basin started Çag in the Jurassic due to an extensional regime, and sediment deposition continued transgressively north during the Late Eocenelayan and Yurtsever (1998) mapped the geological Neogene. Çag setting of the region in detail. Sakınç et al. (1999) defined the age of Ergene Formation as Late Miocene-Pliocene. Okay et al. (2001) noted that the Strandzha Massif was developed as an intra-arc basin in the Senonian and changed to a magmatic arc due to the north-dipping Tethys oceanic lithosphere. Kaymakçı et al. (2007) determined the age of the alkaline volcanic rocks as 4 Ma (Late Miocene) based on 40Ar/39Ar dating. The stratigraphy of the study area is generally divided into two units. The basement unit is composed of metamorphic rocks (Strandzha Massif). The overlying unit is composed of Paleogene and Neogene sediments. The lithologies of the Strandzha Massif were covered by the sediments of the Ergene Basin. The oldest unit of the Strandzha Massif is the Tekedere Group, which consists of schist, pegmatite and gneiss and S¸eytandere metagranite with orthoclase and microcline. The group is exposed in small areas along both sides of the Teke Stream valley and both sides of the S¸eytan Stream valley. The S¸eytandere metagranite shows prominent steep-slope morphology. Isotopic dating using the single zircon PbePb evaporation method shows that there are two magmatic events: one occurred within a short time interval between 312 2 and 315 5 Ma and the other one is dated as 257 6 Ma (Sunal et al., 2008). According to Okay et al. (2008), the Pontides also consist of three terranes: the Strandzha terrane has a Variscan basement, with Carboniferous, Permian granitoids and an epicontinental Triassic to Jurassic sedimentary cover. The units overlying the basement unconformably, from bottom ucak to top, are the Eocene Koyunbaba Formation, the Eocene Sog Formation (Özcan et al., 2010), the Eocene-Oligocene Pınarhisar
lu Formation, and Late MioceneFormation, the Oligocene Sülog Pliocene Ergene Formation (Sakınç et al., 1999). The Eocene Koyunbaba Formation, deposited unconformably on the metamorphic basement, is composed of a sequence of pebblestone, sandstone, limestone, and basal conglomerate. To the west of the ucak ForKırklareli Fault, it is concordantly overlain by the Sog aralar Hill. Formation outcrops mation and is exposed only in Mag are observed east, north and west of Kırklareli city. There are ucak Formation due to its friable lilimited outcrops of the Sog ucak Formation is a reef complex that consists of thology. The Sog cream-white limestone with beds of 1 m thickness or more. It is located in the footwall of the KF in the western part of the study area. The formation has outcrops on both the east and the west sides of the S¸eytan Stream valley, with 40 e50 dip slips on the bedding planes between the S¸eytan Stream valley and west of Kırklareli city. The Eocene-Oligocene Pınarhisar Formation conlayan and Yurtsever, tains limestone, sandstone and marl (Çag 1998). The formation is observed in the hanging wall of the fault, based on the drilling data. The Pınarhisar Formation overlies ucak Formation unconformably. The sandstone and quartz the Sog pebbles observed at the bottom of the formation indicate that these materials were derived from the margin of the Strandzha Massif. Deposition took place in a back reef lagoon facies. The relation of the formation with the reef is intertonguing in some locations and unconformable in others, based on the post-Eocene regression seen over the entire study area. The Upper Oligocene lu Formation is comprised of grey-yellow claystone, siltstone Sülog layan and Yurtsever, 1998). The unit is located and sandstone (Çag ucak Formation and extends to the unconformably on the Sog S¸eytan Stream valley in the east. The dip-slip measurements of the unit to the north of the KF are 25 on the footwall and 30 e40 on the hanging wall in the south of the fault. The youngest Neogene unit in the study area is the Late Miocene-Pliocene Ergene Formation. The unit consists of yellow, dark yellow and yellow-grey pebbles, coarse pebbles, and semi-cemented pebblestone, sandlu stone, and claystone. The Ergene Formation overlies the Sülog Formation unconformably. The KF contacts not only the Ergene ucak formations but also Sog ucak and Sülog lu formations and Sog in the study area (Fig. 2). These formations are covered unconformably by Quaternary alluvium (Fig. 3).
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Fig. 2. Geological map of the investigated area.
3. Field study and data analysis
SL ¼ ðDH=DLÞ L
The morphology of the study area is a highland in north and a depression in south. Morphologically, the Kırklareli Fault forms a boundary between the highland and depression area. The uplift consists of basement rocks and Eocene units, and the depression area consists of the Oligocene and Pliocene units. Morphological indications of the KF can be observed to the north of Koyunbaba ucak Village. It forms the morphological boundary between the Sog and Ergene formations. In the eastern part of the study area, the lu and fault forms the morphological boundary between the Sülog ucak formations, and between the Sülog lu and Koyunbaba Sog formations. The KF morphology linearly extends approximately N105 in the Thrace Region. This lineament controls the morphological and lithological boundaries. A plateau surface cut by deep valleys exists to the northeast of the Kırklareli Fault. In contrast, the topography in the north of the fault has lower relief than the south of the fault. According to the field observations, the Strandzha Mountains and valleys were shaped by the courses of the rivers. Valleys are narrow and deep north of the fault, but wide and shallow south of the fault. The average altitude north of the fault is around 200e240 m, and it is between 150 and 190 m to the south. Hack (1973) suggested the river length-gradient index (SL) to determine whether a river would be in geomorphologic equilibrium, based on the relationship between the river slope and the areal extent of the watershed (Eq. (1)). High SL values indicate deviations in cross-sectional stream profiles from their idealized, equilibrium form, which may be indicative of active and/or recent tectonic activity in an area.
(SL): river length-gradient index, (DH): elevation difference of the river, (DL): length of the river and (L): distance between the valley and peak. The first calculation of the GIs was performed for the study area and Teke Stream. The SL index of the Teke Stream has a high anomaly value peak around the fault from 25 to 208 (see Fig. 4A and Table 1) and the stream is in the class 1 category. In addition, the SL ri Stream shows a moderate anomaly value across the index of the I_g fault from 71 to 113 (see Fig. 4B and Table 1) and the river is in the class 2 category. Finally, the SL index of the S¸eytan Stream shows a low anomaly value across the fault from 43 to 90 (see Fig. 4C and Table 1) and the river is in the class 3 category.
(1)
Table 1 Values of the SL (river length-gradient index) for the study area streams (DH: elevation difference of the river, DL: length of the river and L: distance between the valley and peak). Streams/creeks
Low value
High value
SL anomaly
SL class
Teke ri I_g S¸eytan
25 71 43
208 113 90
High Moderate Low
1 2 3
Ratio of valley-floor width to valley height index (Vf) explains the effects of the tectonism on the profiles of the valley slopes (Eq. (2)). High Vf values indicate low uplift rates, while low Vf values indicate high uplift rates and deeply eroded valleys controlled by
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Fig. 3. Generalized stratigraphy of the investigation area.
tectonics. Thus, the relation between deep erosion and tectonics could be evaluated (Bull, 1977, 1978; Bull and McFadden, 1977; Keller and Pinter, 1996).
Vf ¼ 2:Vfw=ðEld EscÞ þ ðErd EscÞ
(2)
(Vf): ratio of valley-floor widthevalley height, (Vfw): valley-floor width, (Eld): elevation of the left valley divide, (Erd): elevation of the right valley divide and (Esc): elevation of the valley floor. According to the analyses performed along the cross-valley profiles, the Vf values were calculated to be 0.48 for the footwall and 14.12 for the hanging wall of the segment of A in the Teke
Stream valley. The Vf class for Teke Stream valley is defined as 2 (moderate). These values were obtained from the profiles 1 (Vf ¼ 0.48) and 2 (Vf ¼ 14.12) shown in Fig. 5 and Table 2. In addition, the Vf values were calculated to be 2 for the footwall and _ 82 for the hanging wall of the segment of B in the Inci Stream Valley. These values were obtained from the profiles 3 (Vf ¼ 2) and 4 _ (Vf ¼ 82) shown in Fig. 5 and Table 2. The Vf class for Inci Stream Valley is defined 1 (high). Finally, the Vf values were calculated to be 0.36 for the footwall and 9.17 for the hanging wall of the segment of C in the S¸eytan Stream Valley. These values were obtained from the profiles 5 (Vf ¼ 0.36) and 6 (Vf ¼ 9.17) shown in Fig. 5 and Table 2. The Vf class for S¸eytan Stream Valley is defined as 3 (Low).
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Table 2 Values of the Vf (ratio of valley floor width to valley height) for the study area valleys (Vfw: valley-floor width, Eld: elevation of the left valley divide, Erd: elevation of the right valley divide and Esc: elevation of the valley floor). Segments
Valleys
Hangingwall values
Footwall values
Vf class
A B C
Teke _ Inci S¸eytan
14.12 82 9.17
0.48 2 0.36
2 (Moderate) 1 (High) 3 (Low)
lu The hanging wall of the KF includes the Ergene and Sülog formations. The dip-slip measurements obtained on the beds of the Ergene Formation vary between 7 and 10 . The slopes of Ergene Formation change from 40 to 50 in locations near the KF. During the Oligocene-Miocene, the compression ended with moderate folding and faulting, best observed in the Thrace Region (Schindler, 1997). The folds are oriented E-W and NE-SW in the southern part of the study area. In addition, the folds might have developed in accordance with the KF and the other two faults. 4. Fault tectonics The tectonic setting of the Thrace region is controlled by two active tectonic plates: the Anatolian Plate and Eurasia Plate. The
Anatolian Plate rotates counter-clockwise according to previous GPS and tectonic studies, while the Eurasia Plate rotates clockwise (Westaway, 1994; Reilinger et al., 1997; Straub et al., 1997; Armijo et al., 1999; Barka et al., 2000; McClusky et al., 2000; Le Pichon et al., 2003). Additionally, Burchfiel et al. (2008a) state that there is extensional tectonism in east Macedonia, west Bulgaria, north Greece, and northwest Turkey (Thrace Region). Burchfiel et al. (2008b) state that this extension started in Mid-Miocene and is a part of the Aegean extensional system. Deniz and Özener (2010) recognized extensional tectonics through GPS studies in the Thrace Region (Fig. 6). There are several active and inactive faults in the region. The Terzili and North Osmancık faults (Perinçek, 1991; Turgut et al., 1991; Görür and Okay, 1996) are buried faults that have been detected by seismic investigations. The Kırklareli Fault is also a buried fault that forms a morphological boundary between the Strandzha Mountains in the north and the Ergene Basin in the south, a segment of the Terzili and Osmancık fault system. The KF affects the northern border of the Ergene Basin along the Strandzha Mountains and also forms the base of the Strandzha Massif. South of the Strandzha Massif, discontinuity detected by geophysical studies (Bayrak et al., 2004, 2006) is a normal fault exposing a linear structure that continues to the west of Istanbul. The buried KF was detected by drilling and geophysical studies (Perinçek, 1991; Turgut et al., 1991).
ri Stream c) S¸eytan Stream. Fig. 4. Longitudinal river profiles and SL values for a) Teke Stream b) I_g
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Fig. 5. Vf values and cross-valley profiles.
4.1. Seismology The seismicity of the Thrace Region depends on the active faults, including the Kırklareli Fault. A number of major earthquakes in the region occurred in 926e927 (Guidoboni, 1994), and in 1542, 1689, 1752, and 1802 AD (Ambraseys and Finkel, 1991). The 926e927 earthquake completely destroyed many towns and churches, with several ruptures seen on the ground. Several deaths resulted from the June 12th, 1542, earthquake which was felt in Istanbul, Gallipoli, and Edirne. The same earthquake destroyed 1700 houses in Istanbul. The April 25th, 1689 earthquake affected mainly northwest Anatolia, Thrace, and the western coasts of the Black Sea. Many houses, mosques, and churches in Istanbul and Edirne were damaged and the earthquake was felt in Sofia, Bulgaria. The estimated epicenter of this earthquake was in the Maritsa (Meriç) Valley. The July 29th, 1752 earthquake affected primarily the Thrace _ Region. Ibrik Hill, Havsa, and Hasköy were completely destroyed. Many houses and government buildings in Edirne were damaged and also many deaths recorded. Some collapses were noted within the Edirne city walls and the Edirne Castle. The earthquake was felt in Istanbul and Izmir. The October 26th, 1802 earthquake damaged
many houses, marketplaces, mosques and churches in Istanbul and Edirne. Seismic activity attributed to the Ergene Basin has been recorded instrumentally in the region in the 20th century. Several earthquakes (5 M 3) (Fig. 7) are clustered west and east of the KF. The clustering of the earthquakes is due to the lineament structure of the KF aligned approximately east-west. The most important earthquakes were in 1929 (M ¼ 4.5), 1967 (M ¼ 4.4), 1976 (M ¼ 3.7) and 1982 (M ¼ 4.6) according to the Kandilli Observatory earthquake data in the basin. Seismicity of the Ergene Basin is emphasized by a recent study (Horasan et al., 2009). The epicentres of these earthquakes (M 3) concentrated in the basin (around Kırklareli city) (Fig. 7) indicate that the seismic activity still continues. 4.2. Slip rate and geometry Four deep investigation boreholes drilled by the Kırklareli Municipality and DSI (General Directorate of State Hydraulic Works) were used to determine slip rate and geometry of the KF. Boreholes in the area were drilled on the hanging wall of the fault. The
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Fig. 6. GPS data between 2000 and 2006 in the Thrace Region and east Marmara (Deniz and Özener, 2010).
borehole logs of SDK-1 (drill log-1), SDK-2, SDK-3 and SDK-4 wells contain fault traces (Fig. 8). The SDK-1 and SDK-2 wells are the nearest boreholes to the fault and were drilled approximately 1800 m north of Koyunbaba village (see Figs. 2 and 9). The drilled wells were aligned into the same direction with the fault, approximately 100 m far from the fault trace (see Fig. 9). The depth of SDK1 well is 146 m. The first 140 m of this well includes the Ergene Formation, which is accepted as a reference for the bottom level, and the last 6 m is magmatic rock. The magmatic rocks are intrusive, rising through the Kırklareli Fault. The depth of the SDK-2 well is 225 m, with 200 m through the ucak ForErgene Formation and the remainder through the Sog mation. Similarly, the Ergene Formation was cut in the upper levels of the SDK-3 well drilled in the south. The Süloglu Formation is located between 30 m and 130 m depth in the SDK-3 well. The
Pınarhisar Formation continues from 130 m to 321 m. At the bottom of the SDK-3 well, there is a 1 m clay layer and the lower 2 m is granite. These data allow the KF to be defined as a normal fault with a 64 southward inclination. The inclination angle is calculated by the thickness (T) measured as 223 m and distance (D) to the fault plane measured as 110 m in Fig. 9. Thus, the inclination angle is calculated as approximately 64 by using equation (3).
a ¼ arctangðT=DÞ a ¼ arctangð223=110Þ ¼ 63; 74 ¼ w64
(3)
The minimum vertical displacement on the KF calculated with borehole data from the SDK-2 well is about 223 m. The fault is younger than the Pliocene deposits because it cuts through the Late
Fig. 7. Kırklareli Fault and earthquake epicenters (5 > M > 3) in the Thrace Region (Seismic data from the Kandilli Observatory and Earthquake Research Institute database, 2010).
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ucak and Ergene The KF forms the boundary between the Sog formations in the west. The dip of beds on the footwall in the upper ucak Formation is between 21 and 28 SE. However, levels of the Sog beds near the fault are tilted at 45 e50 . The part of the Ergene Formation forming the hanging wall of the fault is the youngest unit in the Ergene Basin, and is generally horizontal. Near the fault, the beds of the formation are backtilted 50 to the northeast in the ri Stream Valley (Fig. 10). Additionally, seismic studies conducted I_g in the area by the Turkish Petroleum Corporation (TPAO) clearly indicated that the Kırklareli Fault is a normal fault (Fig. 11). The seismic reflection data described by Turgut et al. (1991) reveal that the branches of the fault extend towards to the north, and the northernmost branch almost reaches the surface. The extension of the KF could be defined by a lineament in the morphology during the field observations. The KF can be divided into three segments (A, B and C) in the study area based on the morphological evidence. The first segment ucak is located north of Koyunbaba between the Ergene and Sog formations, oriented N105 e110 south of Kayalı and Eriklice (A). The second fault lineament is oriented about N115 e120 in lu and Sog ucak formations (B). Kırklareli city, between the Sülog The last segment of the KF extends approximately N90 east of ucak formations (C). Kırklareli city between the Ergene and Sog ucak Kinematic analysis of the measurements taken from the Sog Formation bedding planes, near the KF, shows a N30o-35 extension (Fig. 12). The paleostress directions calculated for segment A are 238.9 /54.8 for s1, 128.8 /13.9 for s2, and 29.8 /31.4 for s3; for segment B 276.5 /64.3 for s1, 148.4 /15.5 for s2, and 52.9 / 19.7 for s3; and for segment C 215 /41 for s1, 113 /8.3 for s2, and 17.1 /37.4 for s3 (c.f. Turner, 1953). The KF illustrated on Fig. 13 represents normal fault geometry in the study area based on morphological, geological, seismological and borehole data. In addition, the Kırklareli and North Osmancık faults converge at approximately 3 km depth according to seismic reflection data (Turgut et al., 1991; Gürgey, 2009). Fig. 8. Borehole logs, shown in Figs. 1 and 2, used to define the fault (Tas¸, 2002).
Miocene-Pliocene (Ergene Formation). If the offset (O) is taken as 223,000 mm and time (t) is taken as 2 Ma, the displacement rate is calculated as approximately 0.1 mm per year based on Equation (4).
O ¼ Vt 223000 mm ¼ V 2000000 yr
(4)
V (Velocity) ¼ 0.11 ¼ w0.1 mm/y (see Fig. 9)
Fig. 9. SDK-2 borehole data drilled near the fault plane of the Kırklareli Fault. At this point, KF is defined as a normal fault inclined 64 southward.
5. Discussion The KF has an important role in the tectonic model of the Thrace Region. The recent low magnitude earthquakes around Kırklareli city indicate seismic activity of the fault. The geometry of fault described in the study is compatible with the tectonic model of the Ergene Basin of Perinçek (1991), Turgut et al. (1991), Sakınç et al. (1999), Yaltırak (2002), and Kaymakçı et al. (2007). The Kırklareli Fault is a buried fault, which backtilted the units of the Ergene Formation in the basin. While the beds of the Ergene
ri Stream Valley. Fig. 10. Ergene Formation view of backtilting to the northeast in the I_g
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Fig. 11. Structure of the Kırklareli Fault based on two-travel time seismic reflection data (Modified from Turgut et al., 1991).
Formation in the middle of the basin are approximately level, they are inclined 50 NE near the Strandzha Massif. The KF was defined in seismic profiles and oil exploration investigations (Gürgey et al., 2005; Gürgey, 2009), and in the drilling explorations carried out by
TPAO (Turgut et al., 1991). The fault is an indistinct morphological lineament on the surface and probably is the contact between the Strandzha Massif and Ergene Basin. However, the fault plane is unobservable south of the massif. The dip-slip measurements taken ucak Formation are parallel to the fault plane of the from the Sog footwall. The movement of the fault is quite low (w0.1 mm/y). This situation restricts the geological evidence of the fault in the field. Although the KF shows only morphological evidence in the field, it almost reaches the surface in the seismic section (Perinçek, 1991; Turgut et al., 1991; Gürgey et al., 2005; Gürgey, 2009). The fault plane is encountered at 223 m depth of the SDK-2 well in Fig. 9, and the granite intrusive cut in the SDK-1 well (see Fig. 8) is an indication of the KF. The faults located in the Ergene Basin were defined in the previous studies of Perinçek (1991), Turgut et al. (1991), Görür and Okay (1996), Kaymakçı et al. (2007), and Yaltırak (2002). The faults displayed in Fig. 13 indicate that the Terzili Fault is the main fault, and the North Osmancık and Kırklareli faults are the branches of the Terzili Fault in the basin. The Kırklareli Fault is the closest branch of the Terzili and North Osmancık faults to the surface. All of the faults located in the Ergene Basin are buried faults, and the KF investigated by this study should be considered as a part of this fault system. The tectonic studies related to the northwest of the Thrace Region indicate that there is an extensional tectonic regime, starting
ucak Formation near the Kırklareli Fault. Stereogram shows that extension occurred along approxiFig. 12. Kinematical analysis of measurements on bedding planes of the Sog mately N30o-35 orientation, measurements on bedding determined lower hemisphere. Equal-area projections of normal faults and stress directions computed using the PeT method (Turner, 1953). Great circle represents bedding plane; cross represent relative movement of the footwall.
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Fig. 13. Model of tectonic structure of the Ergene Basin between Kırklareli Fault, Terzili strike-slip Fault and North Osmancık normal Fault defined by Perinçek (1991) and Turgut et al. (1991).
in the Middle-Miocene. This extensional tectonism affecting east Macedonia, west Bulgaria, north Greece and northwest Turkey (Thrace Region) is possibly related to the Aegean extensional system (Burchfiel et al., 2008a, 2008b). The KF has developed as a result of this extensional regime as a normal fault. GPS studies undertaken in the region indicated that there is movement towards the northeast (Deniz and Özener, 2010). Kaymakçı et al. (2007) notes that the Thrace Region rotates clockwise, which creates an NE-SW extension and a fault zone (Thrace Fault Zone) related to the extension. This extensional tectonic regime supports the fault kinematics presented in this study. Instrumentally, several low and moderate magnitude earthquakes occurred in the basin. The
movement rate and activity of the fault are quite low compared to the North Anatolian Fault Zone. The relation between the tectonic effects of the KF and morphology was evaluated by relative tectonic activity index (Iat) to verify the presence of the fault. The Iat values were calculated based on the GIs (Table 3). The SL and Vf values obtained in this study were compared with the values given in Bull and McFadden (1977). The values of the Iat were divided into two classes to determine the degree of active tectonics: class 1 (high relative tectonic activity) and class 2 (moderate relative tectonic activity) (Fig. 14). The values obtained through the GIs and the Iat index grades indicate that the activity of the fault is higher in segments A and B than in segment C. The SL index values reach maximum in the areas affected by segment A. The SL values are high in Teke Stream, _ moderate in Inci Stream, and low in S¸eytan Stream. Calculated SL values shown in Fig. 4C indicate that several synthetic faults parallel to the KF should be present. Vf values of the hanging walls are higher that the Vf values of the footwalls, confirmingthe existence of the KF. The buried Kırklareli Fault, capable of producing earthquakes, is located in the northernmost fault system in the basin and is a branch of the North Osmancık normal Fault. Table 3 Iat classification of areas located in front of each segment.
Fig. 14. Classification of the Iat (relative tectonic activity index) in the basin of the study area (SL: river length-gradient index, Vf: ratio of valley floor width to valley height and S/n: total values of classes/number of classes).
Segments of the KF
Streams/ creeks
SL indices
Vf indices
Time Ma
Geological velocity
S/n
Iat class
A A B C
Teke ri I_g _ Inci
1 2 e 3
2 e 1 3
2 2 2 2
0.1 0.1 0.1 0.1
1.5 1 1 3
1 1 1 2
S¸eytan
mm/y mm/y mm/y mm/y
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6. Conclusions This study analysed the tectonic presence of the KF and its effects on the geomorphology of the study area by using the tectonic evidence, GIs, seismology, drilling and seismic reflection data, and field observations. The Kırklareli Fault is located in the northernmost part of the Ergene Basin. In the northwestern part of the study ucak forarea, the fault is the contact between the Ergene and Sog mations. The KF can be divided into three segments (A, B and C) in the study area based on the morphological evidence. The KF is oriented N105 -110 around the south of Kayalı and Eriklice villages, and Kırklareli city. The fault is a part of the morphological lineament extending NW-SE between the Strandzha Mountains and Ergene Basin. Kinematic analysis of measurements on bedding ucak Formation, near the Kırklareli planes, obtained from the Sog normal Fault indicates that the extension is approximately N30 35 . Recorded seismic activity in the region during the 20th century indicates that the faults are active in this region with a maximum recorded magnitude of 4.6. The GPS data indicate northeast movement. Historical earthquakes between 926 and 1802 A.D. caused significant destruction. According to data from wells drilled near to the fault, minimum vertical slip of the Kırklareli Fault is 223 m, and the slip rate is a minimum 0.1 mm/yr. The morphotectonics of the KF were defined by calculating the GIs. The values obtained through the GIs and the Iat index grades supported the existence of the KF in the study area. Segments A and B are rated as class 1 with high tectonic activity, and segment C is defined as class 2, with has moderate tectonic activity. The Vf and SL index values are consistent for the Teke and S¸eytan streams and verify the tectonic effect of the KF on morphology. Field observations and data, the GIs, and velocity calculations support the morphotectonic evidence on the Kırklareli Fault.
Acknowledgements We would like to thank Dr. Ahmet Karakas¸ (Kocaeli University) and K. Ömer Tas¸ (Sakarya University) for their helpful discussion and critical reading. We are also indebted to Dr. Onur Tan (TübitakMarmara Research Centre) for the digital maps and Muzaffer Siyako (Turkish Petroleum Corporation-TPAO) for data support.
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