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The Yenice–Gönen active fault (NW Turkey): Active tectonics and palaeoseismology
Tectonophysics 453 (2008) 263–275
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Tectonophysics j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / t e c t o
The Yenice–Gönen active fault (NW Turkey): Active tectonics and palaeoseismology Akın Kürçer a ,⁎, Alexandros Chatzipetros b, Salih Zeki Tutkun c, Spyros Pavlides b, Özkan Ateş c, Sotiris Valkaniotis b a b c
Çanakkale Onsekiz Mart University, Engineering and Architecture Faculty, Department of Geophysical Engineering, Terzioglu Campus, 17020, Çanakkale, Turkey Aristotle University of Thessaloniki, Department of Geology, GR-54124, Thessaloniki, Greece Çanakkale Onsekiz Mart University, Engineering and Architecture Faculty, Department of Geological Engineering, Terzioglu Campus, 17020, Çanakkale, Turkey
a r t i c l e
i n f o
Article history: Received 20 November 2006 Accepted 13 July 2007 Available online 4 March 2008 Keywords: Yenice–Gönen Fault Yenice–Gönen Earthquake North Anatolian Fault Palaeoseismology Earthquake recurrence interval
a b s t r a c t The Yenice–Gönen Fault (YGF) is one of the most important active tectonic structures in the Biga peninsula. On March 18, 1953, a destructive earthquake (Mw = 7.2) occurred on the YGF, which is considered to be a part of the southern branch of the North Anatolian Fault Zone (NAFZ). A 70 km-long dextral surface rupture formed during the Yenice–Gönen Earthquake (YGE). In this study, structural and palaeoseismological features of the YGF have been investigated. The YGF surface ruptures have been mapped and three trenches were excavated at Muratlar, Karaköy and Seyvan sites. According to the palaeoseismic interpretation and the results of 14C AMS dating, Seyvan trench shows that an earthquake of palaeoseismic age ca. 620 AD ruptured a different strand of the 1953 fault, producing rather significant surface rupture displacement, while there are indications that at least two older events occurred during the past millennia. Another set of trenches excavated near Gönen town (Muratlar village) revealed extensive liquefaction not only during the 1953 event, but also during a previous earthquake, dated at 1440 AD. The Karaköy trench shows no indications of recent reactivations. Based on the trenching results, we estimate a recurrence interval of 660 ± 160 years for large morphogenic earthquakes, creating linear surface ruptures. The maximum reported displacement during the 1953 earthquake was 4.2 m. Taking into account the palaeoseismologically determined earthquake recurrence interval and maximum displacement, slip-rate of the YGF has been calculated to be 6.3 mm/a, which is consistent with present-day velocities determined by GPS measurements. According to the geological investigations, cumulative displacement of the YGF is 2.3 km. This palaeoseismological study contributes to model the behaviour of large seismogenic faults in the Biga Peninsula. © 2008 Elsevier B.V. All rights reserved.
1. Introduction The devastating August 1999 Gölcük (Mw = 7.4) and November 1999 Düzce (Mw = 7.1) earthquakes are the latest reminders that Turkey is located in one of the most seismically active continental regions of the Eastern Mediterranean Region. The activity is driven by the westward movement of the Anatolian Plate along two major fault zones, namely the dextral North Anatolian Fault Zone (NAFZ) and the sinistral East Anatolian Fault Zone (EAFZ), presumably as it is extruded between the northward moving Arabian Plate and the relatively stable Eurasian Plate (Ketin, 1948; McKenzie, 1972; Dewey, 1976; Şengör, 1979; Şengör and Canıtez, 1982; Hempton, 1982; Şengör et al., 1985). The neotectonic regime of Turkey is mainly controlled by the ongoing convergence of the African, Arabian and Eurasian Plates, which began in the Middle Miocene, and result in the westward migration of the Anatolian Plate (Ketin, 1948; McKenzie, 1970, 1972; Dewey and Şengör, ⁎ Corresponding author. E-mail addresses: [email protected] (A. Kürçer), [email protected] (A. Chatzipetros), [email protected] (S.Z. Tutkun), [email protected] (S. Pavlides), [email protected] (Ö. Ateş), [email protected] (S. Valkaniotis). 0040-1951/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.tecto.2007.07.010
1979; Şengör and Yılmaz, 1981; Jackson and McKenzie, 1984, 1988) (Fig. 1). The NAFZ and the EAFZ are two of the most important active continental transform fault zones in the Eastern Mediterranean Region. The NAFZ is probably the most important active fault zone in this area, as testified by major historical and minor instrumental seismicity. The NAFZ is a dextral strike-slip fault zone more than 1200 km-long, which forms the northern boundary of the westward moving Anatolian Plate. The width of the zone trace ranges from 100 m in the east, whereas it widens up to 5 km to the west. In general, while the fault exhibits strike-slip faulting with reverse component to the east, due to the northward movement of the Arabian Plate, its western part shows a normal component due to its interaction with the Aegean area extensional regime. The NAFZ starts around Karlıova triple junction to the east and runs NW to Vezirköprü, where it makes a left bend and continues westward. The NAFZ contains few master segments of more than 100 km in length and several smaller segments shorter than 100 km. From east to west, the main NAFZ segments are the Erzincan segment (350 km, ruptured in 1939), the Ladik–Tosya segment (260 km, ruptured in 1943), the Gerede segment (180 km, ruptured in 1944), the Saros segment (uncertain length, more than
264 A. Kürçer et al. / Tectonophysics 453 (2008) 263–275 Fig. 1. Western segments of North Anatolian Fault Zone (modified from Şaroğlu et al., 1992) and historical earthquakes in the Biga Peninsula and surroundings at between 32 AD and 1900 (modified from Ambraseys and Finkel, 1991), See inset map for location and general geotectonic setting.
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Fig. 2. Geological map of Yenice–Gönen area (modified and simplified from Kürçer 2006).
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100 km, ruptured in 1912), the Manyas segment (ruptured in 1964) and the Yenice–Gönen segment (70 km, ruptured in 1953). Most of the earthquakes occurred sequentially in a westward progression (Stein et al., 1997). East of Adapazarı it splits into a northern, a central and a southern branch extending in the Marmara Sea and northern Aegean regions, illustrating a horse-tail character (Şengör and Barka, 1992) (Fig. 1). The northern branch starts from southeast of Sapanca Lake and then passes through the south of Gulf of İzmit, Marmara Sea, Saros Gulf and Northern Aegean Sea. The central branch follows the path southeast of Sapanca Lake, Geyve, Pamukova, south of İznik Lake, southern coast of Marmara Sea and Kapıdağ Peninsula, where it makes a left bend and continues southwest in the Biga Peninsula. The central branch of NAFZ consists of several en echelon faults in the Biga Peninsula. These faults are the Etili Fault, the Sarıköy–İnova Fault, the Biga–Çan Fault Zone and the Edincik Fault from northeast to southwest, respectively. The southern branch of NAFZ consists of the Bursa Fault, the Uluabat Fault, the Manyas Fault, the Yenice–Gönen Fault and the Edremit Fault (Fig. 1). Long-term seismicity, GPS measurements and geological data suggest that the northern branch of the NAFZ is more active than the other two southern branches (Barka, 1997). The Aegean Region is undergoing NNE–SSW trending extension. At the Turkish coast of the Aegean, the Western Anatolian Graben System (WAGS) consists of several grabens and horsts bounded by oblique E– W trending normal faults. The Biga Peninsula area is a transition zone between the WAGS and the westernmost segments of NAFZ. While the north-eastern and northern parts of Biga Peninsula are deformed by WAGS, in the central part of the Biga Peninsula, the deformation is primarily controlled by NAFZ. In the study area, the deformation is related to both WAGS and the western part of NAFZ and it may be defined as a transition zone. In this paper, the geological and structural features of the YGF and its surroundings, including the surface ruptures of the YGE, have been mapped in detail (Fig. 2). The rock ages in the study area range from Carboniferous to Quaternary belonging to the basement, Karakaya Complex tectonic unit, Mesozoic marine deposits, the Kanlıoba Ophiolithic Mélange, Oligocene–Miocene volcanic intrusive bodies and a complex mainly clastic Neogene sequence.
Biga Peninsula, such as fault scarps, asymmetric valleys, triangular facets, linear valleys, deflected stream channels, etc. The presence of geothermal fields in the Biga Peninsula (Kırkgeçit, Gönen, Ekşidere, Ilıcaoba, Çan, Tepeköy, Hıdırlar, Bardakçılar, Güre, Derman, etc.), as well as historical and instrumental seismicity, are also evidence of active tectonics. The Biga Peninsula has been deformed by both the WAGS and the westernmost part of NAFZ (Gürer et al., 2006). This combined deformation has formed dextral strike-slip faults with normal component, tectonic basins related to these faults and other deformation structures with obvious transcurrent component. These faults have been described by Barka and Kadinsky-Cade (1988), Siyako et al. (1989), Herece (1990), Barka (1992) and Şaroğlu et al. (1992). The fault fabric of the area consists of several NE–SW trending strike-slip faults parallel to each other, showing en echelon geometry forming several fault-bounded basins. The relative displacement vectors in the Biga Peninsula have been defined by a dense network of GPS stations (Straub and Kahle, 1995; Straub et al., 1997; Reilinger et al., 1997; Meade et al., 2002; Kreemer et al., 2004) showing that the NAFZ accommodates about 20–25 mm/a of dextral motion, with Anatolia moving westward relative to Eurasia. The GPS data indicate that most of this motion takes place along the northern branch of the NAFZ (Straub, 1996). The other two branches of NAFZ are less active with respect to the northern branch. Meade et al. (2002) suggest 6.8 ± 2.3 mm/a strike-slip and 0.8 ± 3.4 mm/a normal fault rates for the vicinity of the study area (see also, Meade et al., 2002) (Fig. 3). Similarly, Kreemer et al. (2004) suggest 7 mm/a strike-slip rates for the vicinity of the study area. 3. Seismicity and the Yenice–Gönen Earthquake Many destructive earthquakes have occurred during historical times. The historical earthquakes of the study area and its vicinity are shown in Fig. 1. The Yenice–Gönen Fault (YGF) is one of the most important active faults in the Biga Peninsula. On March 18, 1953, a strong (Mw = 7.2) linear
2. Tectonic setting The structural setting of the Biga Peninsula has been modified through three successive deformation stages: the Karakaya orogenesis, the Tertiary–Alpide orogenesis and Late Tertiary tectonic movements. The first phase of Karakaya orogenesis caused the superposition of the various Karakaya Complex units. During the second phase of Karakaya orogenesis, structural sequences have been deformed due to faulting. One of the most important Early Tertiary– Alpide events in the Biga Peninsula is the obduction of the ophiolitic mélange units on continental rocks. Most of the tectonic contact between these two units is either covered by Neogene rocks or reactivated as Late Tertiary faults. In the Biga Peninsula, small lake basins, such as Çan, Etili, Kalkım and Yenice are tectonic depressions bounded by still active strike-slip faults; therefore, it seems that they have subsided considerably between Oligocene and Pleistocene. Structural lines in the Biga Peninsula controlled the development of depositional basins during the Pliocene (Herece, 1985). This strike-slip faulting is confined within a NE–SW trending zone between Edremit Bay and Bandırma. Due to the neotectonic activity (Miocene–present) in the Biga Peninsula, pre-Miocene surfaces have been uplifted at some places (Kazdağ etc) or subsided at some other places (Ezine–Bayramiç, Kalkım–Hamdibey–Pazarköy, Etili, Yenice, Gönen, Biga etc). Apart from the wide-area uplift or subsidence, several morphotectonic features represent evidence of recent deformation in the
Fig. 3. Active faults in the Biga peninsula. Fault map is modified from Şaroğlu et al. (1992); the numbers indicate slip-rate values from GPS measurements (Meade et al., 2002).
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Fig. 4. General morphological view of the Yenice–Gönen Fault (YGF) and the 1953 surface ruptures. SRTM (Shuttle Radar Topography Mission) data is used for the digital elevation model.The focal mechanism of the earthquake is also shown.
morphogenic earthquake (sensu Caputo, 2005) occurred on the YGF, causing 263 casualties. The epicentre of the main shock was located approximately 12 km east of Yenice town (Karasukabaklar village), and
focal depth determinations varied from 10 to 12 km (Herece,1985). A 70km-long surface rupture formed along the YGF during the earthquake between east of Gönen and southwest of Yenice (Fig. 4).
Fig. 5. a. Fault scarp south of Gökçesu village (view towards SW). b. General morphological view of Yenice–Gönen Fault (near Kalfa village) (view towards south).
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Fig. 6. a. 1.5 m deflection on a path during the earthquake (sketch from Ketin and Roesly, 1953) b. View towards NW of the same site today (Photo taken from Kürçer, 2006).
The first detailed macroseismic studies on the YGF were performed by Pınar (1953), Ketin and Roesly (1953). The fault trace of the 1953 event has been investigated in detail for the first time by Herece (1985). Tokay and Dirik (2004) have studied the rupture-fault geometry and slip distribution of YGF. Kürçer (2006) investigated the neotectonic and some palaeoseismological features of the YGF. The surface rupture of the 1953 YGE is shown in detail in Fig. 2. It trends N 85° W between Sepetçi and Saraçlar villages, N 65°–75° E between Korudeğirmeni and Seyvan villages, E–W south of Yenice and N 80° E near Sazak village. The surface rupture affects Neogene sediments to the east of Gönen (near of Sepetçi village), then displaces Tertiary volcanics and Quaternary deposits east of Korudeğirmeni village, where the fault morphology is particularly outstanding (Fig. 5a and b). The fault can be traced through the alluvial area of Gönen and westward across the Neogene deposits near Muratlar village, where the fault scarp is still evident. During the earthquake, the southern block was displaced 10 cm vertically and 1.5 m right-laterally (Fig. 6). This location has been selected as the first trench site (Ketin site). The fault trace continues as a contact between Tertiary volcanics and Neogene deposits trending N 70° E for about 2 km, up to the weathered Tertiary volcanics, northwest of the Kumköy village. It makes a left step between Kumköy and Gaybular villages. The fault trace then crosses through a small Jurassic limestone outcrop northwest of Gaybular village. The fault trace again displaces volcanics at its SW continuation, north of Ortaoba village. A normal displacement of about 1.2 m along the fault scarp south of Karaköy village has been observed, where the fault scarp is still evident (Fig. 7a). This area has been selected as a second trench site (Karaköy site). The trace goes on through alluvial deposits, which were displaced during the earthquake by 1.5 m of right lateral offset south of Çakır village. Then the fault extends to the southwest, crossing the road between Yenice–Kalkım and continuing south–southwest of Seyvan. Between Çakır and Seyvan, the fault trace is well exposed as a scarp approximately 1–1.5 m high. Here the fault break indicates that, in
Fig. 7. a. Fault scarp south of Karaköy (view towards SE). b. Fault scarp south of Seyvan village (view towards SE). c. Fault plane south of Yenice town (view towards S). d. Triangular facets in Sazak valley (view towards S).
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The fault trace then makes a south-westerly bend to Yenice and extends through the valley south of Sazak village. Here it marks the southern border of the valley, which is underlain by the metamorphic rocks of the Karakaya Complex. Dextrally offset triangular facets are visible in the Sazak valley (Fig. 7d). Further SW, the fault trace at the northern side of the valley is made of several en echelon faults that cut metamorphic rocks and seem to terminate somewhere between Eskiyayla and Zeybekçayırı villages. 4. Geophysical investigations
Fig. 8. a. ERT section of Muratlar-1 profile. The dashed lines point out the fracture zone. b. Seismic section of Muratlar-1 profile. Rectangle indicates the trench site.
addition to dextral movement, there was also a 1.3 m normal displacement of the northern block during the earthquake south of Seyvan village (Fig. 7b). This location has been selected for the third trench site (Seyvan site). During the mapping of the 1953 YGE fracture zone, a number of scarps in different stages of erosion were noted in these locations. These scarps indicate multiple faulting events during the Quaternary and are typical in a variety of tectonic settings (e.g. Chatzipetros and Pavlides (1998). The fault trace then enters a granite body, changing its direction from SW to W, south of Yenice. Before the 1953 earthquake, Yenice was located right on the fault some 800 m away from its present position. The YGF shows an oblique character south of Yenice, where the fault plane is exposed at several sites (Fig. 7c).
Fig. 9. a. ERT section of Muratlar-2 profile. The dashed lines point out the fracture zone. b. Seismic section of Muratlar-2 profile. The lines delimit the fracture zone.
During July 2004 several trenches were excavated at three sites along the surface rupture of YGE: (1) Ketin (Muratlar village area), (2) Karaköy (south of Karaköy) and (3) Seyvan (southwest of Seyvan). All these sites were selected on the basis of the ascertained 1953 surface rupture, as well as on local morphological setting and shallow geophysical investigations like Electrical Resistivity Tomographies (ERT) and seismic refraction profiles. Details on each site and their association with the 1953 fault rupture have been described in the previous paragraphs. At Muratlar and Karaköy trench locations, seismic refraction and electrical resistivity methods were applied, with two and one measured profiles, respectively. At Seyvan site, unfavourable weather conditions did not allow any measurements. ABEM Terraloc MK6 for seismic refraction and Scintrex SARIS multi electrode resistivity meter for DCR measurements were employed. Survey parameters were selected according to field conditions and target depth and were kept fix for all the profiles. Seismic method is based on recording the travel time of an elastic wave created by hitting a steel plate with a hammer, refracted from a subsurface, and received via geophones on the surface. Geophone interval was set at 1.5 m. During the survey, the P-wave travel times were considered. First arrivals to each geophone are marked and extracted from the data. Commercial package, SeisOPT was used to evaluate the data. The result of 2D inversion for each profile reveals horizontal and vertical velocity variations of subsurface.
Fig. 10. a. ERT section of Karaköy profile. The dashed lines point out the fracture zones. b. Seismic section of Karaköy profile. Rectangle indicates the trench site.
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For the electrical resistivity method, direct current is injected to the ground via two electrodes, and potential differences are recorded between two potential electrodes (see Caputo et al., 2003, for a detailed description of the methodology). Recorded potential differences depend on the electrode configuration and geological structures. Multi-electrode system of the Scintrex Saris was used in this work. The system has 25 electrodes and does the recordings according to selected configurations, simultaneously. Electrode spacing was set at 1.5 m. Ten levels of measurements were carried out and 130 apparent resistivity data were collected in each profile using Wenner– Schlumberger configuration. Collected data were evaluated using the two-dimensional modelling code (Loke, 1999). In data processing stage, all collected data were evaluated with the algorithm of 2-D inversion. “0” point of P-wave velocity sections and resistivity sections aren't shown at same points. “0” point of seismic sections are ahead 1.5 m from resistivity sections. 4.1. Ketin site (Muratlar area) In Muratlar area two 50 m-long profiles, parallel to each other, were measured (Muratlar-1 and Muratlar-2). In Muratlar-1 seismic section, lateral variation of the velocity is observed between 15 and 25 m (Fig. 8b). In this section, no vertical displacement seems to occur. Similarly, in Muratlar-1 resistivity section (Fig. 8a) a strong horizontal gradient has been observed at about 20 m. In Muratlar-2 section, a
disturbance zone is observed between 14 and 20 m (Fig. 9b). Because the surface is covered by the modern units, fracture has not reached the surface. The same anomaly has been observed in Muratlar-2 resistivity section (Fig. 9a). 4.2. Karaköy site Only one profile was measured in this area (Karaköy profile). In Karaköy seismic section, a low-velocity zone is observed between 20 and 24 m (Fig. 10b) and the seismic horizons show 3 m vertical displacement documenting the cumulative activity of several linear morphogenic earthquakes. Also, the Karaköy resistivity section (Fig. 10a) shows strong lateral variations at about 24 m and between 12 and 15 m. Because of the difference between seismic refraction and ERT methods, prepared geophysical sections cannot be the same. According to the geophysical surveys (processing and modelling) inferred location of fracture zones shows similarities with surface geological data. 5. Palaeoseismology and dating Based on the results of surface mapping and geophysical prospecting, the optimal sites for trenching were selected. The following paragraphs describe the palaeoseismological details and information obtained from the trenches.
Fig. 11. Microtopographical maps of the trench sites. The maps were made on the basis of detailed field surveying. Thick lines represent parts of the ERT and seismic survey profiles, while gray boxes indicate the location of the trenches.
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Fig. 12. a. Log of the east wall of KET-1 trench. b. Log of the west wall of KET-1 trench. West wall is inverted for easier comparison. Numbers refer to the following: 1. Modern soil, dark grey–brown coloured. Medium to coarse grained sand, occasionally silty clay. Few pebbles of up to 2 cm. Well-developed. Contact with lower unit is gradual. 2. Possibly the lowermost part of unit 1. Light brown–reddish. Material is the same as unit 1. The contact with the lower units is unclear at places. It contains sand, possibly injected from unit 3. 3. Liquefied sand. Lateral boundaries unclear at places. Off-whitish coloured. Vent shows clear “flow” structure. 4. Same material as unit 3, but cut by it. It shows locally flow marks. 5. Medium grained reddish brown sand. There are plentiful caliche flakes near the contact with units 3 and 4. 6. Red brown fine sand–clay. It is a massive layer with occasional caliche flakes and ejected (through cracks) light gray fine sand. Solid circles indicate sampling points with their respective radiocarbon dates. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
5.1. Ketin site trenches (Muratlar area) Two trenches (KET-1 and KET-2) were excavated in this site near Muratlar village. Ketin site is located close to Gönen town (Fig. 2), and was named by the authors after the famous Turkish geologist that described in detail the surface ruptures of the 1953 earthquake. The location of the trenches was surveyed using precise microtopographical prospecting (Fig. 11). The survey showed traces of the 1953 surface ruptures, although they appeared to be eroded and modified by human activities. The KET-1 trench was excavated at the site where the maximum dextral displacement was observed in 1953. Based on the microtopographical and geophysical prospecting, this site was expected to yield the best results regarding the recent history of the fault. KET-1 trench has a N–S strike and is 5 m wide and 3 m deep. The logs of the walls (Fig. 12) have revealed that the stratigraphy consists of a sequence of red brown deposits, which are intruded by a vent of liquefied light yellow sand. The sand originates from a lower horizon, visible at the
lowermost part of the trench, and has a distinct flowing texture. The sequence is covered by two soil horizons affected by the 1953 surface ruptures. Based on the above mentioned stratigraphy and the analysis of Table 1 Microstratigraphic correlation and timing of the palaeoevents in trench KET-1 #
Dating
Description of effects
Remarks
1 2
1953 1440?
Surface ruptures Liquefied sand and surface ruptures covered by modern soil
3
?
Older generation of liquefied sand
The event is visible in both trenches The dating of the event is confined by the ages of the overlying and the underlying layers of liquefied sand (510 ± 40 and 760 ± 40 a BP respectively). The event age is tentatively assumed to coincide with the lowermost section of the overlying soil horizon. The dating of the event is not certain, as the stratigraphy does not allow for the discrimination of datable units.
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Fig. 13. Photomosaic (a) and log (b) of the west wall of KAR-1 trench. No fault is evident in this trench. Numbers refer to units as follows: 1. Modern soil with gradual transition towards lower unit. Not very well-developed. 2. Medium grained sand with occasional pebbles and small clay lenses. Brown–reddish brown coloured. 3. Possibly colluvial material. Medium to coarse grained with a lot of pebbles and chunks of bedrock (andesite, basalt, etc.). Also contains lenses of yellowish coarse sand and reddish clay (see unit 4). Unit 3a is more fine-grained than unit 3b. 4. Brown red fine sand and clay. Variable thickness, forms alternations and lenses. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
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Table 2 Microstratigraphic correlation and timing of the palaeoevents in trench SEY-1 #
Dating
Description of effects
Remarks
1
1953
Surface ruptures
2
620 AD?
Ruptures covered by a colluvial wedge
3–4
During the past 4.5 ka
Older generations of colluvia
The event is visible in the northernmost set of fractures that cut through the modern surface. The colluvial wedge was deposited immediately after an earthquake that deformed the surface and produced a hanging normal scarp. The age of this event is confined between 620 AD (wedge date) and 1,270 AD (overlying layer date). Due to the depositional processes for the formation of the wedge, the oldest date should be considered as the most likely dating of the penultimate event in this trench The dating of the events is not certain. They produced the colluvial units that lay below the most recent colluvial wedge and the palaeosoil.
the relationships between layers and structural characteristics, three events were identified in this trench. The timing and the stratigraphic correlation is given in Table 1. The main feature of this trench is the liquefied sand, which is directly associated to a previous earthquake, dated at 1440 AD. This date corresponds to the radiocarbon date obtained for the overlying soil layer, as it is considered as deposited immediately after the morphogenic earthquake. The 1953 earthquake did not produce any liquefaction phenomenon at this site due to a lower water table. This vent of liquefied sand intrudes an older generation of liquefaction features, on which it forms a mushroom-shaped sand volcano. There was no available material for this event, but it is evident that an older earthquake, similar in effects to that of 1440 AD occurred along the same fault affecting the site in a similar way. A smaller auxiliary trench (5 m long and 1.5 m depth) was excavated parallel and close to KET-1 trench. Its log confirmed the observations made in the main KET-1 trench. The surface ruptures, as well as the liquefied sand are present here too, but the sand vent is located about 2 m north of the fault, which is not the case in KET-1. This is a further indication that the liquefaction is not associated to the 1953 earthquake. 5.2. Karaköy site trench This site is located near Karaköy village (Fig. 2) and includes a scarp at the base of which, according to local witnesses, surface fractures formed during the 1953 earthquake. The morphological expression of the scarp (Fig. 11) is very prominent; nevertheless, its origin is rather erosional, as it defines the southern border of the Karaköy valley, which shows a distinct asymmetry towards the scarp with the stream flowing very close to the scarp toe. One trench (KAR-1) was excavated at this site, 11 m long and 2.5 to 3 m deep (Fig. 13). Logging of the trench walls shows that there is actually no fault at this site. The layers detected in this trench are a sequence of colluvial and fluvial deposits, showing characteristic lateral transition in places. The layers do not appear to be deformed in any way. It is therefore very probable that the detected geophysical anomalies are due to the carried composition of the material deposited at the toe of the scarp. Taking into account the overall morphology of the larger area (elongated asymme-
Fig. 15. Evolution sketch of faulting sequence in Seyvan site. The fault is manifested in two distinct strands, the newest (1953) one being downslope. Numbers correspond to the numbering of SEY-1 trench. a. A L. Holocene earthquake ruptures the surface. b. The oldest colluvium (colluvial wedge 1) is formed. c. A palaeosoil is formed on top of the first colluvium. d. The earthquake of 620 AD ruptures the surface and causes the formation of colluvial wedge 2. e. The modern soil is ruptured by the 1953 earthquake.
trical valley), the actual fault should be located under the alluvial river deposits and any evidence of the 1953 earthquake surface effects has been destroyed by erosion or covered by modern fluvial sediments.
Fig. 14. a. Log of the west wall of SEY-1 trench. b. Log of the east wall of SEY-1 trench. East wall is inverted for easier comparison. Numbers refer to the following: 1. Brown-coloured, weakly developed modern soil. It consists of fine to medium grained sand with a few angular pebbles coming from the footwall further upslope. 2. Colluvial wedge associated with a palaeoevent on the southernmost fault. Off-white coloured, consisting of medium grained sand with several pebbles. 3. Dark, gray, well-developed palaeosoil. It has a lot of organic material and its transition to the lower unit is gradual at places. 4. Light brown–off white coloured, massive colluvial sequence consisting of medium to coarse grained sand with many pebbles of up to 2 cm in diameter. Several large rock chunks. Lenses and local concentrations of clay. 5. Brown-coloured clay with sparse pebbles. Transition with lower unit is gradual. 6. Brown–green coloured clay with sparse pebbles. Solid circles indicate sampling points for radiocarbon dating. Their ages are also shown. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
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5.3. Seyvan site trench Seyvan site is located at a slope south of Seyvan village (Fig. 2), where the 1953 surface ruptures produced an elongated scarp a few cm high. About 2 m of dextral displacement were reported at this site. The scarp morphology (Fig. 11) is a gentle slope with a very distinctive scarp near its toe. One trench was excavated at this site (SEY-1), 10 m long and 3 to 3.5 m deep. The walls show a sequence of colluvia, derived from the upper part of the slope (Fig. 14). It is also evident that there are two sets of fractures. The northernmost fractures cut through the modern surface and are attributed to the 1953 event. The southernmost set of fractures stops at the base of a colluvial wedge that has a very characteristic shape and covers a palaeosoil which is located under modern soil. The earthquake events traced in this trench are summarised in Table 2. Apart from the 1953 event, at least three more events are recorded, the penultimate one being dated at 620 AD (Fig. 15). 6. Discussion and conclusions The already available and newly gained geological data, prove that the YGF has been active at least since the Miocene. This prolonged activity has shaped the morphology and structural setting of the area, and is still going on today, as it is evident from historical and instrumental large and small earthquakes associated with it. The kinematic indicators (slickenline analysis) show a neotectonic deformation that is consistent with the other major faults of the Biga Peninsula. Based on the radiocarbon dates of the earthquakes recorded in the trenches excavated along this fault, the mean recurrence interval for significant, linear morphogenic earthquakes is calculated at 660 ± 160 years. Although the recurrence interval seems quite large for the NAFZ, it must be taken into account that it refers to only a branch of its western termination, therefore it cannot be extrapolated for the main fault zone. This recurrence interval does not consider smaller earthquakes that are likely not morphogenic, or too small to be detected in the trenches. Another implication of the present study is that the YGF does not behave uniformly throughout its length. Despite its linearity, it does not present the same kinematic character, neither the same palaeoseismic history. This can be explained in two ways. Firstly, the strike of the fault changes along its length. If the active stress field is considered stable throughout the area, it affects the different fault segments in a different way, thus producing different surface effects. Alternatively, being a primarily strike-slip fault, it forms splays in areas of geometrical bends. Although these splays are not evident in all cases, the surface ruptures, especially if deflected near the surface due to the deformation of less competent materials follow or form different strands. This is the reason why KET-1, KET-2 and SEY-1 trenches tell different stories about the recent deformation of the YGF. According to GPS data, mean horizontal displacement for the area of Yenice–Gönen is 6.8 mm/a (Fig. 3). This displacement is not necessarily associated with major co-seismic ruptures, but reflects a rather general trend of the broader area. The maximum co-seismic displacement reported for the 1953 earthquake is 4.2 m. If one takes into account the mean recurrence interval of 660 ± 160 years, as derived from the study of the palaeoseismological trenches, the mean interpolated annual displacement is 6.4 + 2.0–1.3 mm/a, which is in very good agreement with the displacement determined by GPS. This consistency shows a steady deformational behaviour of YGF during historical times. It was not possible to measure the amount of horizontal displacement of past earthquakes, as the trenches only showed the vertical component of displacement. It seems however that the vertical (normal) displacement, as measured in SEY-1 trench, is similar to the 1953 one, so we may tentatively assume that the previous
earthquakes were of comparable magnitude, provided that the fault segments behave in a uniform way during the past few centuries. In conclusion, the YGF is an active fault of moderate to strong activity. It accommodates a part of the overall NAFZ activity both in terms of recurrence interval and mean annual displacement. As far as seismic hazard is concerned, the geological information shows that there is no immediate threat from this particular fault. The area is however susceptible to distant earthquakes from other Biga Peninsula faults, for which palaeoseismological information is still to be gained. Acknowledgements Eutizio Vittori, Stefan Shanov and an anonymous reviewer provided valuable corrections and additions to the original manuscript. We thank the mayor of Gönen for providing open access to his community, and in assisting with land access. We are grateful to Emin Ulugergerli and Yıldırım Gündogdu for processing the geophysical investigations. This work was supported by TÜBİTAK. Grant no: 103 Y 007. References Ambraseys, N.N., Finkel, C.F., 1991. Long-term seismicity of Istanbul and of the Marmara Sea region. Terra Nova 3, 527–539. Barka, A.A., 1992. The North Anatolian Fault Zone. Ann. Tecton. 6, 164–195. Barka, A., 1997. Neotectonics of the Marmara Sea region, Active tectonics of the Nortwestern Anatolia—The Marmara Poly-Project.vdf Hochschuiverlag AG an der ETH Zürich, pp. 55–87. Barka, A.A., Kadinsky-Cade, K., 1988. Strike-slip fault geometry in Turkey and its influence on earthquake activity. Tectonics 7 (3), 663–684. Caputo, R., 2005. Ground effects of large morphogenic earthquakes. J. Geodyn. 40, 113–118. Caputo, R., Piscitelli, S., Oliveto, A., Rizzo, E., Lapenna, V., 2003. The use of electrical resistivity tomographies in active tectonics: examples from the Tyrnavos Basin, Greece. J. Geodyn. 36, 19–35. Chatzipetros, A., Pavlides, S., 1998. A quantitative morphotectonic approach to the study of active faults; Mygdonia basin, northern Greece. Bull. Geol. Soc. Greece 32 (1), 155–164. Dewey, J.W., 1976. Seismicity of northern Anatolia: Seismological Society of America Bulletin, vol. 66, pp. 843–868. Dewey, J.F., Şengör, A.M.C., 1979. Aegean and surrounding regions: complex multiplate and continuum tectonics in a convergent zone. Geol. Soc. Amer. Bull. Part 1 90, 84–92. Gürer, Ö.F., Sangu, E., Özburan, M., 2006. Neotectonics of the SW Marmara Region, NW Anatolia, Turkey. Geol. Mag. 143 (2), 229–241. Hempton, M.R., 1982, Structure of the northern margin of the Bitlis suture zone near Sivrice, southeastern Turkey, PhD Dissertation, SUNY Albany, p. 563. Herece, E., 1985, The fault trace of 1953 Yenice–Gönen Earthquake and some examples of recent tectonic events in the Biga Peninsula of Northwest Turkey: Penn State University, Ms. S. Thesis 143 s. Herece, E., 1990. 1953 Yenice–Gönen deprem kırığı ve Kuzey Anadolu fay sisteminin Biga Yarımadası'ndaki uzantıları, MTA Dergisi, vol. 111, pp. 47–59. Jackson, J., McKenzie, D.P., 1984. Active tectonics of the Alpine–Himalayan Belt between western Turkey and Pakistan. Geophys. J. R. Astron. Soc., 77, 185–246. Jackson, J.A., McKenzie, D.P., 1988. The relationship between plate motions and seismic moment tensors, and the rates of active deformation in the Mediterranean and Middle East. Geophys. J. Int. 93, 45–73. Ketin, I., 1948. Über die Tekronisch - Mechanischen Folgerunges aus Grossen Anatolischen Erdbeden des Letzten Dezenniums. Geol Rundsch 36, 77–83. Ketin, I., Roesly, F., 1953. Makroseismische Untersuchungen über das nordwestanatolische Beben vom 18. Marz 1953. Eclogae Geol. Helv. 46, 187–208. Kreemer, C., Chamot-Roke, N., Le Pichon, X., 2004. Constraints on the evolution and vertical coherency of deformation in the North Aegean from a comparison of geodetic, geologic and seismologic data. Earth Planet. Sci. Lett. 225, 329–346. Kürçer, A., 2006. Neotectonical features of the vicinity of Yenice–Gönen and palaeoseismology of March 18, 1953 (Mw:7,2) Yenice–Gönen Earthquake Fault, NW Turkey, M.S. Thesis. Çanakkale Onsekiz Mart University, Natural and Applied Sciences Institute, p. 170. (in Turkish with English abstract). Loke, M.H., 1999. Electrical imaging surveys for environmental and engineering studies, pp. 1–57. www.abem.se. McKenzie, D.P., 1970. Plate tectonics of the Mediterranean region. Nature 226, 239–241. McKenzie, D.P., 1972. Active tectonics of the Mediterranean region. Geophys. J. R. Astron. Soc. 30 (2), 109–185. Meade, B., Hager, B., Reilinger, R., 2002. Estimates of seismic potential in the Marmara region from block models of secular deformation constrained by GPS measurements. Bull. Seismol. Soc. Am. 92 (1), 208–215. Pınar, N., 1953. Preliminary Note on the Earthquake of Yenice Gönen, Turkey, March 18, 1953. Bull. Seismol. Soc. Am., vol. 43, pp. 307–310. Reilinger, R.E., McClusky, S.C., Oral, M.B., King, R.W., Toksoz, M.N., Barka, A.A., Kinik, I., Lenk, O., Sanli, I., 1997. Global positioning system measurements of present
A. Kürçer et al. / Tectonophysics 453 (2008) 263–275 day crustal movements in the Arabian–African–Eurasian plate collision zone. J. Geophys. Res. 102, 9983–9999. Şaroğlu, F., Emre, Ö. and Kuşcu, I., 1992, Active fault map of Turkey, (scale: 1:1000, 000). General Direct. Mineral Res. Explor. (MTA), Ankara, Turkey. Şengör, A.M.C., 1979. On some 50% extension in the Aegean area and its implications for orogenic reconstructions in the Taurides. Rapp. Comm. Int. Mer. Mediterr. 25/26 (2a) pp. 41–42. Şengör, A.M.C., Canıtez, N., 1982. The North Anatolian Fault. In: Berekhemer, H., Hsu, K. (Eds.), Alpine Mediterranean Geodynamics. Deuticke, Vienna, pp. 205–216. Şengör, A.M.C., Yılmaz, Y., 1981. Tethyan evolution of Turkey: a plate tectonic approach. Tectonophysics, 75, 181–242. Şengör, A.M.C., Görür, N., Şaroğlu, F., 1985. Strike-slip faulting and related basin formation in zones tectonic escape: Turkey as a case study. In: Biddle, K.T., ChristieBlick, N. (Eds.), Strike-slip Deformation, Basin Formation and Sedimentation. Soc. Econ. Paleontol. Mineral. Spec. Publ., 37, pp. 227–264. Şengör, A.M.C., Barka, A., 1992. Evolution of escape related strike-slip systems: implications for distribution of collision orogens. Abstracts, 29th IGC, Japan.
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Tectonophysics j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / t e c t o
The Yenice–Gönen active fault (NW Turkey): Active tectonics and palaeoseismology Akın Kürçer a ,⁎, Alexandros Chatzipetros b, Salih Zeki Tutkun c, Spyros Pavlides b, Özkan Ateş c, Sotiris Valkaniotis b a b c
Çanakkale Onsekiz Mart University, Engineering and Architecture Faculty, Department of Geophysical Engineering, Terzioglu Campus, 17020, Çanakkale, Turkey Aristotle University of Thessaloniki, Department of Geology, GR-54124, Thessaloniki, Greece Çanakkale Onsekiz Mart University, Engineering and Architecture Faculty, Department of Geological Engineering, Terzioglu Campus, 17020, Çanakkale, Turkey
a r t i c l e
i n f o
Article history: Received 20 November 2006 Accepted 13 July 2007 Available online 4 March 2008 Keywords: Yenice–Gönen Fault Yenice–Gönen Earthquake North Anatolian Fault Palaeoseismology Earthquake recurrence interval
a b s t r a c t The Yenice–Gönen Fault (YGF) is one of the most important active tectonic structures in the Biga peninsula. On March 18, 1953, a destructive earthquake (Mw = 7.2) occurred on the YGF, which is considered to be a part of the southern branch of the North Anatolian Fault Zone (NAFZ). A 70 km-long dextral surface rupture formed during the Yenice–Gönen Earthquake (YGE). In this study, structural and palaeoseismological features of the YGF have been investigated. The YGF surface ruptures have been mapped and three trenches were excavated at Muratlar, Karaköy and Seyvan sites. According to the palaeoseismic interpretation and the results of 14C AMS dating, Seyvan trench shows that an earthquake of palaeoseismic age ca. 620 AD ruptured a different strand of the 1953 fault, producing rather significant surface rupture displacement, while there are indications that at least two older events occurred during the past millennia. Another set of trenches excavated near Gönen town (Muratlar village) revealed extensive liquefaction not only during the 1953 event, but also during a previous earthquake, dated at 1440 AD. The Karaköy trench shows no indications of recent reactivations. Based on the trenching results, we estimate a recurrence interval of 660 ± 160 years for large morphogenic earthquakes, creating linear surface ruptures. The maximum reported displacement during the 1953 earthquake was 4.2 m. Taking into account the palaeoseismologically determined earthquake recurrence interval and maximum displacement, slip-rate of the YGF has been calculated to be 6.3 mm/a, which is consistent with present-day velocities determined by GPS measurements. According to the geological investigations, cumulative displacement of the YGF is 2.3 km. This palaeoseismological study contributes to model the behaviour of large seismogenic faults in the Biga Peninsula. © 2008 Elsevier B.V. All rights reserved.
1. Introduction The devastating August 1999 Gölcük (Mw = 7.4) and November 1999 Düzce (Mw = 7.1) earthquakes are the latest reminders that Turkey is located in one of the most seismically active continental regions of the Eastern Mediterranean Region. The activity is driven by the westward movement of the Anatolian Plate along two major fault zones, namely the dextral North Anatolian Fault Zone (NAFZ) and the sinistral East Anatolian Fault Zone (EAFZ), presumably as it is extruded between the northward moving Arabian Plate and the relatively stable Eurasian Plate (Ketin, 1948; McKenzie, 1972; Dewey, 1976; Şengör, 1979; Şengör and Canıtez, 1982; Hempton, 1982; Şengör et al., 1985). The neotectonic regime of Turkey is mainly controlled by the ongoing convergence of the African, Arabian and Eurasian Plates, which began in the Middle Miocene, and result in the westward migration of the Anatolian Plate (Ketin, 1948; McKenzie, 1970, 1972; Dewey and Şengör, ⁎ Corresponding author. E-mail addresses: [email protected] (A. Kürçer), [email protected] (A. Chatzipetros), [email protected] (S.Z. Tutkun), [email protected] (S. Pavlides), [email protected] (Ö. Ateş), [email protected] (S. Valkaniotis). 0040-1951/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.tecto.2007.07.010
1979; Şengör and Yılmaz, 1981; Jackson and McKenzie, 1984, 1988) (Fig. 1). The NAFZ and the EAFZ are two of the most important active continental transform fault zones in the Eastern Mediterranean Region. The NAFZ is probably the most important active fault zone in this area, as testified by major historical and minor instrumental seismicity. The NAFZ is a dextral strike-slip fault zone more than 1200 km-long, which forms the northern boundary of the westward moving Anatolian Plate. The width of the zone trace ranges from 100 m in the east, whereas it widens up to 5 km to the west. In general, while the fault exhibits strike-slip faulting with reverse component to the east, due to the northward movement of the Arabian Plate, its western part shows a normal component due to its interaction with the Aegean area extensional regime. The NAFZ starts around Karlıova triple junction to the east and runs NW to Vezirköprü, where it makes a left bend and continues westward. The NAFZ contains few master segments of more than 100 km in length and several smaller segments shorter than 100 km. From east to west, the main NAFZ segments are the Erzincan segment (350 km, ruptured in 1939), the Ladik–Tosya segment (260 km, ruptured in 1943), the Gerede segment (180 km, ruptured in 1944), the Saros segment (uncertain length, more than
264 A. Kürçer et al. / Tectonophysics 453 (2008) 263–275 Fig. 1. Western segments of North Anatolian Fault Zone (modified from Şaroğlu et al., 1992) and historical earthquakes in the Biga Peninsula and surroundings at between 32 AD and 1900 (modified from Ambraseys and Finkel, 1991), See inset map for location and general geotectonic setting.
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Fig. 2. Geological map of Yenice–Gönen area (modified and simplified from Kürçer 2006).
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100 km, ruptured in 1912), the Manyas segment (ruptured in 1964) and the Yenice–Gönen segment (70 km, ruptured in 1953). Most of the earthquakes occurred sequentially in a westward progression (Stein et al., 1997). East of Adapazarı it splits into a northern, a central and a southern branch extending in the Marmara Sea and northern Aegean regions, illustrating a horse-tail character (Şengör and Barka, 1992) (Fig. 1). The northern branch starts from southeast of Sapanca Lake and then passes through the south of Gulf of İzmit, Marmara Sea, Saros Gulf and Northern Aegean Sea. The central branch follows the path southeast of Sapanca Lake, Geyve, Pamukova, south of İznik Lake, southern coast of Marmara Sea and Kapıdağ Peninsula, where it makes a left bend and continues southwest in the Biga Peninsula. The central branch of NAFZ consists of several en echelon faults in the Biga Peninsula. These faults are the Etili Fault, the Sarıköy–İnova Fault, the Biga–Çan Fault Zone and the Edincik Fault from northeast to southwest, respectively. The southern branch of NAFZ consists of the Bursa Fault, the Uluabat Fault, the Manyas Fault, the Yenice–Gönen Fault and the Edremit Fault (Fig. 1). Long-term seismicity, GPS measurements and geological data suggest that the northern branch of the NAFZ is more active than the other two southern branches (Barka, 1997). The Aegean Region is undergoing NNE–SSW trending extension. At the Turkish coast of the Aegean, the Western Anatolian Graben System (WAGS) consists of several grabens and horsts bounded by oblique E– W trending normal faults. The Biga Peninsula area is a transition zone between the WAGS and the westernmost segments of NAFZ. While the north-eastern and northern parts of Biga Peninsula are deformed by WAGS, in the central part of the Biga Peninsula, the deformation is primarily controlled by NAFZ. In the study area, the deformation is related to both WAGS and the western part of NAFZ and it may be defined as a transition zone. In this paper, the geological and structural features of the YGF and its surroundings, including the surface ruptures of the YGE, have been mapped in detail (Fig. 2). The rock ages in the study area range from Carboniferous to Quaternary belonging to the basement, Karakaya Complex tectonic unit, Mesozoic marine deposits, the Kanlıoba Ophiolithic Mélange, Oligocene–Miocene volcanic intrusive bodies and a complex mainly clastic Neogene sequence.
Biga Peninsula, such as fault scarps, asymmetric valleys, triangular facets, linear valleys, deflected stream channels, etc. The presence of geothermal fields in the Biga Peninsula (Kırkgeçit, Gönen, Ekşidere, Ilıcaoba, Çan, Tepeköy, Hıdırlar, Bardakçılar, Güre, Derman, etc.), as well as historical and instrumental seismicity, are also evidence of active tectonics. The Biga Peninsula has been deformed by both the WAGS and the westernmost part of NAFZ (Gürer et al., 2006). This combined deformation has formed dextral strike-slip faults with normal component, tectonic basins related to these faults and other deformation structures with obvious transcurrent component. These faults have been described by Barka and Kadinsky-Cade (1988), Siyako et al. (1989), Herece (1990), Barka (1992) and Şaroğlu et al. (1992). The fault fabric of the area consists of several NE–SW trending strike-slip faults parallel to each other, showing en echelon geometry forming several fault-bounded basins. The relative displacement vectors in the Biga Peninsula have been defined by a dense network of GPS stations (Straub and Kahle, 1995; Straub et al., 1997; Reilinger et al., 1997; Meade et al., 2002; Kreemer et al., 2004) showing that the NAFZ accommodates about 20–25 mm/a of dextral motion, with Anatolia moving westward relative to Eurasia. The GPS data indicate that most of this motion takes place along the northern branch of the NAFZ (Straub, 1996). The other two branches of NAFZ are less active with respect to the northern branch. Meade et al. (2002) suggest 6.8 ± 2.3 mm/a strike-slip and 0.8 ± 3.4 mm/a normal fault rates for the vicinity of the study area (see also, Meade et al., 2002) (Fig. 3). Similarly, Kreemer et al. (2004) suggest 7 mm/a strike-slip rates for the vicinity of the study area. 3. Seismicity and the Yenice–Gönen Earthquake Many destructive earthquakes have occurred during historical times. The historical earthquakes of the study area and its vicinity are shown in Fig. 1. The Yenice–Gönen Fault (YGF) is one of the most important active faults in the Biga Peninsula. On March 18, 1953, a strong (Mw = 7.2) linear
2. Tectonic setting The structural setting of the Biga Peninsula has been modified through three successive deformation stages: the Karakaya orogenesis, the Tertiary–Alpide orogenesis and Late Tertiary tectonic movements. The first phase of Karakaya orogenesis caused the superposition of the various Karakaya Complex units. During the second phase of Karakaya orogenesis, structural sequences have been deformed due to faulting. One of the most important Early Tertiary– Alpide events in the Biga Peninsula is the obduction of the ophiolitic mélange units on continental rocks. Most of the tectonic contact between these two units is either covered by Neogene rocks or reactivated as Late Tertiary faults. In the Biga Peninsula, small lake basins, such as Çan, Etili, Kalkım and Yenice are tectonic depressions bounded by still active strike-slip faults; therefore, it seems that they have subsided considerably between Oligocene and Pleistocene. Structural lines in the Biga Peninsula controlled the development of depositional basins during the Pliocene (Herece, 1985). This strike-slip faulting is confined within a NE–SW trending zone between Edremit Bay and Bandırma. Due to the neotectonic activity (Miocene–present) in the Biga Peninsula, pre-Miocene surfaces have been uplifted at some places (Kazdağ etc) or subsided at some other places (Ezine–Bayramiç, Kalkım–Hamdibey–Pazarköy, Etili, Yenice, Gönen, Biga etc). Apart from the wide-area uplift or subsidence, several morphotectonic features represent evidence of recent deformation in the
Fig. 3. Active faults in the Biga peninsula. Fault map is modified from Şaroğlu et al. (1992); the numbers indicate slip-rate values from GPS measurements (Meade et al., 2002).
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Fig. 4. General morphological view of the Yenice–Gönen Fault (YGF) and the 1953 surface ruptures. SRTM (Shuttle Radar Topography Mission) data is used for the digital elevation model.The focal mechanism of the earthquake is also shown.
morphogenic earthquake (sensu Caputo, 2005) occurred on the YGF, causing 263 casualties. The epicentre of the main shock was located approximately 12 km east of Yenice town (Karasukabaklar village), and
focal depth determinations varied from 10 to 12 km (Herece,1985). A 70km-long surface rupture formed along the YGF during the earthquake between east of Gönen and southwest of Yenice (Fig. 4).
Fig. 5. a. Fault scarp south of Gökçesu village (view towards SW). b. General morphological view of Yenice–Gönen Fault (near Kalfa village) (view towards south).
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Fig. 6. a. 1.5 m deflection on a path during the earthquake (sketch from Ketin and Roesly, 1953) b. View towards NW of the same site today (Photo taken from Kürçer, 2006).
The first detailed macroseismic studies on the YGF were performed by Pınar (1953), Ketin and Roesly (1953). The fault trace of the 1953 event has been investigated in detail for the first time by Herece (1985). Tokay and Dirik (2004) have studied the rupture-fault geometry and slip distribution of YGF. Kürçer (2006) investigated the neotectonic and some palaeoseismological features of the YGF. The surface rupture of the 1953 YGE is shown in detail in Fig. 2. It trends N 85° W between Sepetçi and Saraçlar villages, N 65°–75° E between Korudeğirmeni and Seyvan villages, E–W south of Yenice and N 80° E near Sazak village. The surface rupture affects Neogene sediments to the east of Gönen (near of Sepetçi village), then displaces Tertiary volcanics and Quaternary deposits east of Korudeğirmeni village, where the fault morphology is particularly outstanding (Fig. 5a and b). The fault can be traced through the alluvial area of Gönen and westward across the Neogene deposits near Muratlar village, where the fault scarp is still evident. During the earthquake, the southern block was displaced 10 cm vertically and 1.5 m right-laterally (Fig. 6). This location has been selected as the first trench site (Ketin site). The fault trace continues as a contact between Tertiary volcanics and Neogene deposits trending N 70° E for about 2 km, up to the weathered Tertiary volcanics, northwest of the Kumköy village. It makes a left step between Kumköy and Gaybular villages. The fault trace then crosses through a small Jurassic limestone outcrop northwest of Gaybular village. The fault trace again displaces volcanics at its SW continuation, north of Ortaoba village. A normal displacement of about 1.2 m along the fault scarp south of Karaköy village has been observed, where the fault scarp is still evident (Fig. 7a). This area has been selected as a second trench site (Karaköy site). The trace goes on through alluvial deposits, which were displaced during the earthquake by 1.5 m of right lateral offset south of Çakır village. Then the fault extends to the southwest, crossing the road between Yenice–Kalkım and continuing south–southwest of Seyvan. Between Çakır and Seyvan, the fault trace is well exposed as a scarp approximately 1–1.5 m high. Here the fault break indicates that, in
Fig. 7. a. Fault scarp south of Karaköy (view towards SE). b. Fault scarp south of Seyvan village (view towards SE). c. Fault plane south of Yenice town (view towards S). d. Triangular facets in Sazak valley (view towards S).
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The fault trace then makes a south-westerly bend to Yenice and extends through the valley south of Sazak village. Here it marks the southern border of the valley, which is underlain by the metamorphic rocks of the Karakaya Complex. Dextrally offset triangular facets are visible in the Sazak valley (Fig. 7d). Further SW, the fault trace at the northern side of the valley is made of several en echelon faults that cut metamorphic rocks and seem to terminate somewhere between Eskiyayla and Zeybekçayırı villages. 4. Geophysical investigations
Fig. 8. a. ERT section of Muratlar-1 profile. The dashed lines point out the fracture zone. b. Seismic section of Muratlar-1 profile. Rectangle indicates the trench site.
addition to dextral movement, there was also a 1.3 m normal displacement of the northern block during the earthquake south of Seyvan village (Fig. 7b). This location has been selected for the third trench site (Seyvan site). During the mapping of the 1953 YGE fracture zone, a number of scarps in different stages of erosion were noted in these locations. These scarps indicate multiple faulting events during the Quaternary and are typical in a variety of tectonic settings (e.g. Chatzipetros and Pavlides (1998). The fault trace then enters a granite body, changing its direction from SW to W, south of Yenice. Before the 1953 earthquake, Yenice was located right on the fault some 800 m away from its present position. The YGF shows an oblique character south of Yenice, where the fault plane is exposed at several sites (Fig. 7c).
Fig. 9. a. ERT section of Muratlar-2 profile. The dashed lines point out the fracture zone. b. Seismic section of Muratlar-2 profile. The lines delimit the fracture zone.
During July 2004 several trenches were excavated at three sites along the surface rupture of YGE: (1) Ketin (Muratlar village area), (2) Karaköy (south of Karaköy) and (3) Seyvan (southwest of Seyvan). All these sites were selected on the basis of the ascertained 1953 surface rupture, as well as on local morphological setting and shallow geophysical investigations like Electrical Resistivity Tomographies (ERT) and seismic refraction profiles. Details on each site and their association with the 1953 fault rupture have been described in the previous paragraphs. At Muratlar and Karaköy trench locations, seismic refraction and electrical resistivity methods were applied, with two and one measured profiles, respectively. At Seyvan site, unfavourable weather conditions did not allow any measurements. ABEM Terraloc MK6 for seismic refraction and Scintrex SARIS multi electrode resistivity meter for DCR measurements were employed. Survey parameters were selected according to field conditions and target depth and were kept fix for all the profiles. Seismic method is based on recording the travel time of an elastic wave created by hitting a steel plate with a hammer, refracted from a subsurface, and received via geophones on the surface. Geophone interval was set at 1.5 m. During the survey, the P-wave travel times were considered. First arrivals to each geophone are marked and extracted from the data. Commercial package, SeisOPT was used to evaluate the data. The result of 2D inversion for each profile reveals horizontal and vertical velocity variations of subsurface.
Fig. 10. a. ERT section of Karaköy profile. The dashed lines point out the fracture zones. b. Seismic section of Karaköy profile. Rectangle indicates the trench site.
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For the electrical resistivity method, direct current is injected to the ground via two electrodes, and potential differences are recorded between two potential electrodes (see Caputo et al., 2003, for a detailed description of the methodology). Recorded potential differences depend on the electrode configuration and geological structures. Multi-electrode system of the Scintrex Saris was used in this work. The system has 25 electrodes and does the recordings according to selected configurations, simultaneously. Electrode spacing was set at 1.5 m. Ten levels of measurements were carried out and 130 apparent resistivity data were collected in each profile using Wenner– Schlumberger configuration. Collected data were evaluated using the two-dimensional modelling code (Loke, 1999). In data processing stage, all collected data were evaluated with the algorithm of 2-D inversion. “0” point of P-wave velocity sections and resistivity sections aren't shown at same points. “0” point of seismic sections are ahead 1.5 m from resistivity sections. 4.1. Ketin site (Muratlar area) In Muratlar area two 50 m-long profiles, parallel to each other, were measured (Muratlar-1 and Muratlar-2). In Muratlar-1 seismic section, lateral variation of the velocity is observed between 15 and 25 m (Fig. 8b). In this section, no vertical displacement seems to occur. Similarly, in Muratlar-1 resistivity section (Fig. 8a) a strong horizontal gradient has been observed at about 20 m. In Muratlar-2 section, a
disturbance zone is observed between 14 and 20 m (Fig. 9b). Because the surface is covered by the modern units, fracture has not reached the surface. The same anomaly has been observed in Muratlar-2 resistivity section (Fig. 9a). 4.2. Karaköy site Only one profile was measured in this area (Karaköy profile). In Karaköy seismic section, a low-velocity zone is observed between 20 and 24 m (Fig. 10b) and the seismic horizons show 3 m vertical displacement documenting the cumulative activity of several linear morphogenic earthquakes. Also, the Karaköy resistivity section (Fig. 10a) shows strong lateral variations at about 24 m and between 12 and 15 m. Because of the difference between seismic refraction and ERT methods, prepared geophysical sections cannot be the same. According to the geophysical surveys (processing and modelling) inferred location of fracture zones shows similarities with surface geological data. 5. Palaeoseismology and dating Based on the results of surface mapping and geophysical prospecting, the optimal sites for trenching were selected. The following paragraphs describe the palaeoseismological details and information obtained from the trenches.
Fig. 11. Microtopographical maps of the trench sites. The maps were made on the basis of detailed field surveying. Thick lines represent parts of the ERT and seismic survey profiles, while gray boxes indicate the location of the trenches.
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Fig. 12. a. Log of the east wall of KET-1 trench. b. Log of the west wall of KET-1 trench. West wall is inverted for easier comparison. Numbers refer to the following: 1. Modern soil, dark grey–brown coloured. Medium to coarse grained sand, occasionally silty clay. Few pebbles of up to 2 cm. Well-developed. Contact with lower unit is gradual. 2. Possibly the lowermost part of unit 1. Light brown–reddish. Material is the same as unit 1. The contact with the lower units is unclear at places. It contains sand, possibly injected from unit 3. 3. Liquefied sand. Lateral boundaries unclear at places. Off-whitish coloured. Vent shows clear “flow” structure. 4. Same material as unit 3, but cut by it. It shows locally flow marks. 5. Medium grained reddish brown sand. There are plentiful caliche flakes near the contact with units 3 and 4. 6. Red brown fine sand–clay. It is a massive layer with occasional caliche flakes and ejected (through cracks) light gray fine sand. Solid circles indicate sampling points with their respective radiocarbon dates. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
5.1. Ketin site trenches (Muratlar area) Two trenches (KET-1 and KET-2) were excavated in this site near Muratlar village. Ketin site is located close to Gönen town (Fig. 2), and was named by the authors after the famous Turkish geologist that described in detail the surface ruptures of the 1953 earthquake. The location of the trenches was surveyed using precise microtopographical prospecting (Fig. 11). The survey showed traces of the 1953 surface ruptures, although they appeared to be eroded and modified by human activities. The KET-1 trench was excavated at the site where the maximum dextral displacement was observed in 1953. Based on the microtopographical and geophysical prospecting, this site was expected to yield the best results regarding the recent history of the fault. KET-1 trench has a N–S strike and is 5 m wide and 3 m deep. The logs of the walls (Fig. 12) have revealed that the stratigraphy consists of a sequence of red brown deposits, which are intruded by a vent of liquefied light yellow sand. The sand originates from a lower horizon, visible at the
lowermost part of the trench, and has a distinct flowing texture. The sequence is covered by two soil horizons affected by the 1953 surface ruptures. Based on the above mentioned stratigraphy and the analysis of Table 1 Microstratigraphic correlation and timing of the palaeoevents in trench KET-1 #
Dating
Description of effects
Remarks
1 2
1953 1440?
Surface ruptures Liquefied sand and surface ruptures covered by modern soil
3
?
Older generation of liquefied sand
The event is visible in both trenches The dating of the event is confined by the ages of the overlying and the underlying layers of liquefied sand (510 ± 40 and 760 ± 40 a BP respectively). The event age is tentatively assumed to coincide with the lowermost section of the overlying soil horizon. The dating of the event is not certain, as the stratigraphy does not allow for the discrimination of datable units.
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Fig. 13. Photomosaic (a) and log (b) of the west wall of KAR-1 trench. No fault is evident in this trench. Numbers refer to units as follows: 1. Modern soil with gradual transition towards lower unit. Not very well-developed. 2. Medium grained sand with occasional pebbles and small clay lenses. Brown–reddish brown coloured. 3. Possibly colluvial material. Medium to coarse grained with a lot of pebbles and chunks of bedrock (andesite, basalt, etc.). Also contains lenses of yellowish coarse sand and reddish clay (see unit 4). Unit 3a is more fine-grained than unit 3b. 4. Brown red fine sand and clay. Variable thickness, forms alternations and lenses. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
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Table 2 Microstratigraphic correlation and timing of the palaeoevents in trench SEY-1 #
Dating
Description of effects
Remarks
1
1953
Surface ruptures
2
620 AD?
Ruptures covered by a colluvial wedge
3–4
During the past 4.5 ka
Older generations of colluvia
The event is visible in the northernmost set of fractures that cut through the modern surface. The colluvial wedge was deposited immediately after an earthquake that deformed the surface and produced a hanging normal scarp. The age of this event is confined between 620 AD (wedge date) and 1,270 AD (overlying layer date). Due to the depositional processes for the formation of the wedge, the oldest date should be considered as the most likely dating of the penultimate event in this trench The dating of the events is not certain. They produced the colluvial units that lay below the most recent colluvial wedge and the palaeosoil.
the relationships between layers and structural characteristics, three events were identified in this trench. The timing and the stratigraphic correlation is given in Table 1. The main feature of this trench is the liquefied sand, which is directly associated to a previous earthquake, dated at 1440 AD. This date corresponds to the radiocarbon date obtained for the overlying soil layer, as it is considered as deposited immediately after the morphogenic earthquake. The 1953 earthquake did not produce any liquefaction phenomenon at this site due to a lower water table. This vent of liquefied sand intrudes an older generation of liquefaction features, on which it forms a mushroom-shaped sand volcano. There was no available material for this event, but it is evident that an older earthquake, similar in effects to that of 1440 AD occurred along the same fault affecting the site in a similar way. A smaller auxiliary trench (5 m long and 1.5 m depth) was excavated parallel and close to KET-1 trench. Its log confirmed the observations made in the main KET-1 trench. The surface ruptures, as well as the liquefied sand are present here too, but the sand vent is located about 2 m north of the fault, which is not the case in KET-1. This is a further indication that the liquefaction is not associated to the 1953 earthquake. 5.2. Karaköy site trench This site is located near Karaköy village (Fig. 2) and includes a scarp at the base of which, according to local witnesses, surface fractures formed during the 1953 earthquake. The morphological expression of the scarp (Fig. 11) is very prominent; nevertheless, its origin is rather erosional, as it defines the southern border of the Karaköy valley, which shows a distinct asymmetry towards the scarp with the stream flowing very close to the scarp toe. One trench (KAR-1) was excavated at this site, 11 m long and 2.5 to 3 m deep (Fig. 13). Logging of the trench walls shows that there is actually no fault at this site. The layers detected in this trench are a sequence of colluvial and fluvial deposits, showing characteristic lateral transition in places. The layers do not appear to be deformed in any way. It is therefore very probable that the detected geophysical anomalies are due to the carried composition of the material deposited at the toe of the scarp. Taking into account the overall morphology of the larger area (elongated asymme-
Fig. 15. Evolution sketch of faulting sequence in Seyvan site. The fault is manifested in two distinct strands, the newest (1953) one being downslope. Numbers correspond to the numbering of SEY-1 trench. a. A L. Holocene earthquake ruptures the surface. b. The oldest colluvium (colluvial wedge 1) is formed. c. A palaeosoil is formed on top of the first colluvium. d. The earthquake of 620 AD ruptures the surface and causes the formation of colluvial wedge 2. e. The modern soil is ruptured by the 1953 earthquake.
trical valley), the actual fault should be located under the alluvial river deposits and any evidence of the 1953 earthquake surface effects has been destroyed by erosion or covered by modern fluvial sediments.
Fig. 14. a. Log of the west wall of SEY-1 trench. b. Log of the east wall of SEY-1 trench. East wall is inverted for easier comparison. Numbers refer to the following: 1. Brown-coloured, weakly developed modern soil. It consists of fine to medium grained sand with a few angular pebbles coming from the footwall further upslope. 2. Colluvial wedge associated with a palaeoevent on the southernmost fault. Off-white coloured, consisting of medium grained sand with several pebbles. 3. Dark, gray, well-developed palaeosoil. It has a lot of organic material and its transition to the lower unit is gradual at places. 4. Light brown–off white coloured, massive colluvial sequence consisting of medium to coarse grained sand with many pebbles of up to 2 cm in diameter. Several large rock chunks. Lenses and local concentrations of clay. 5. Brown-coloured clay with sparse pebbles. Transition with lower unit is gradual. 6. Brown–green coloured clay with sparse pebbles. Solid circles indicate sampling points for radiocarbon dating. Their ages are also shown. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
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5.3. Seyvan site trench Seyvan site is located at a slope south of Seyvan village (Fig. 2), where the 1953 surface ruptures produced an elongated scarp a few cm high. About 2 m of dextral displacement were reported at this site. The scarp morphology (Fig. 11) is a gentle slope with a very distinctive scarp near its toe. One trench was excavated at this site (SEY-1), 10 m long and 3 to 3.5 m deep. The walls show a sequence of colluvia, derived from the upper part of the slope (Fig. 14). It is also evident that there are two sets of fractures. The northernmost fractures cut through the modern surface and are attributed to the 1953 event. The southernmost set of fractures stops at the base of a colluvial wedge that has a very characteristic shape and covers a palaeosoil which is located under modern soil. The earthquake events traced in this trench are summarised in Table 2. Apart from the 1953 event, at least three more events are recorded, the penultimate one being dated at 620 AD (Fig. 15). 6. Discussion and conclusions The already available and newly gained geological data, prove that the YGF has been active at least since the Miocene. This prolonged activity has shaped the morphology and structural setting of the area, and is still going on today, as it is evident from historical and instrumental large and small earthquakes associated with it. The kinematic indicators (slickenline analysis) show a neotectonic deformation that is consistent with the other major faults of the Biga Peninsula. Based on the radiocarbon dates of the earthquakes recorded in the trenches excavated along this fault, the mean recurrence interval for significant, linear morphogenic earthquakes is calculated at 660 ± 160 years. Although the recurrence interval seems quite large for the NAFZ, it must be taken into account that it refers to only a branch of its western termination, therefore it cannot be extrapolated for the main fault zone. This recurrence interval does not consider smaller earthquakes that are likely not morphogenic, or too small to be detected in the trenches. Another implication of the present study is that the YGF does not behave uniformly throughout its length. Despite its linearity, it does not present the same kinematic character, neither the same palaeoseismic history. This can be explained in two ways. Firstly, the strike of the fault changes along its length. If the active stress field is considered stable throughout the area, it affects the different fault segments in a different way, thus producing different surface effects. Alternatively, being a primarily strike-slip fault, it forms splays in areas of geometrical bends. Although these splays are not evident in all cases, the surface ruptures, especially if deflected near the surface due to the deformation of less competent materials follow or form different strands. This is the reason why KET-1, KET-2 and SEY-1 trenches tell different stories about the recent deformation of the YGF. According to GPS data, mean horizontal displacement for the area of Yenice–Gönen is 6.8 mm/a (Fig. 3). This displacement is not necessarily associated with major co-seismic ruptures, but reflects a rather general trend of the broader area. The maximum co-seismic displacement reported for the 1953 earthquake is 4.2 m. If one takes into account the mean recurrence interval of 660 ± 160 years, as derived from the study of the palaeoseismological trenches, the mean interpolated annual displacement is 6.4 + 2.0–1.3 mm/a, which is in very good agreement with the displacement determined by GPS. This consistency shows a steady deformational behaviour of YGF during historical times. It was not possible to measure the amount of horizontal displacement of past earthquakes, as the trenches only showed the vertical component of displacement. It seems however that the vertical (normal) displacement, as measured in SEY-1 trench, is similar to the 1953 one, so we may tentatively assume that the previous
earthquakes were of comparable magnitude, provided that the fault segments behave in a uniform way during the past few centuries. In conclusion, the YGF is an active fault of moderate to strong activity. It accommodates a part of the overall NAFZ activity both in terms of recurrence interval and mean annual displacement. As far as seismic hazard is concerned, the geological information shows that there is no immediate threat from this particular fault. The area is however susceptible to distant earthquakes from other Biga Peninsula faults, for which palaeoseismological information is still to be gained. Acknowledgements Eutizio Vittori, Stefan Shanov and an anonymous reviewer provided valuable corrections and additions to the original manuscript. We thank the mayor of Gönen for providing open access to his community, and in assisting with land access. We are grateful to Emin Ulugergerli and Yıldırım Gündogdu for processing the geophysical investigations. This work was supported by TÜBİTAK. Grant no: 103 Y 007. References Ambraseys, N.N., Finkel, C.F., 1991. Long-term seismicity of Istanbul and of the Marmara Sea region. Terra Nova 3, 527–539. Barka, A.A., 1992. The North Anatolian Fault Zone. Ann. Tecton. 6, 164–195. Barka, A., 1997. Neotectonics of the Marmara Sea region, Active tectonics of the Nortwestern Anatolia—The Marmara Poly-Project.vdf Hochschuiverlag AG an der ETH Zürich, pp. 55–87. Barka, A.A., Kadinsky-Cade, K., 1988. Strike-slip fault geometry in Turkey and its influence on earthquake activity. Tectonics 7 (3), 663–684. Caputo, R., 2005. Ground effects of large morphogenic earthquakes. J. Geodyn. 40, 113–118. Caputo, R., Piscitelli, S., Oliveto, A., Rizzo, E., Lapenna, V., 2003. The use of electrical resistivity tomographies in active tectonics: examples from the Tyrnavos Basin, Greece. J. Geodyn. 36, 19–35. Chatzipetros, A., Pavlides, S., 1998. A quantitative morphotectonic approach to the study of active faults; Mygdonia basin, northern Greece. Bull. Geol. Soc. Greece 32 (1), 155–164. Dewey, J.W., 1976. Seismicity of northern Anatolia: Seismological Society of America Bulletin, vol. 66, pp. 843–868. Dewey, J.F., Şengör, A.M.C., 1979. Aegean and surrounding regions: complex multiplate and continuum tectonics in a convergent zone. Geol. Soc. Amer. Bull. Part 1 90, 84–92. Gürer, Ö.F., Sangu, E., Özburan, M., 2006. Neotectonics of the SW Marmara Region, NW Anatolia, Turkey. Geol. Mag. 143 (2), 229–241. Hempton, M.R., 1982, Structure of the northern margin of the Bitlis suture zone near Sivrice, southeastern Turkey, PhD Dissertation, SUNY Albany, p. 563. Herece, E., 1985, The fault trace of 1953 Yenice–Gönen Earthquake and some examples of recent tectonic events in the Biga Peninsula of Northwest Turkey: Penn State University, Ms. S. Thesis 143 s. Herece, E., 1990. 1953 Yenice–Gönen deprem kırığı ve Kuzey Anadolu fay sisteminin Biga Yarımadası'ndaki uzantıları, MTA Dergisi, vol. 111, pp. 47–59. Jackson, J., McKenzie, D.P., 1984. Active tectonics of the Alpine–Himalayan Belt between western Turkey and Pakistan. Geophys. J. R. Astron. Soc., 77, 185–246. Jackson, J.A., McKenzie, D.P., 1988. The relationship between plate motions and seismic moment tensors, and the rates of active deformation in the Mediterranean and Middle East. Geophys. J. Int. 93, 45–73. Ketin, I., 1948. Über die Tekronisch - Mechanischen Folgerunges aus Grossen Anatolischen Erdbeden des Letzten Dezenniums. Geol Rundsch 36, 77–83. Ketin, I., Roesly, F., 1953. Makroseismische Untersuchungen über das nordwestanatolische Beben vom 18. Marz 1953. Eclogae Geol. Helv. 46, 187–208. Kreemer, C., Chamot-Roke, N., Le Pichon, X., 2004. Constraints on the evolution and vertical coherency of deformation in the North Aegean from a comparison of geodetic, geologic and seismologic data. Earth Planet. Sci. Lett. 225, 329–346. Kürçer, A., 2006. Neotectonical features of the vicinity of Yenice–Gönen and palaeoseismology of March 18, 1953 (Mw:7,2) Yenice–Gönen Earthquake Fault, NW Turkey, M.S. Thesis. Çanakkale Onsekiz Mart University, Natural and Applied Sciences Institute, p. 170. (in Turkish with English abstract). Loke, M.H., 1999. Electrical imaging surveys for environmental and engineering studies, pp. 1–57. www.abem.se. McKenzie, D.P., 1970. Plate tectonics of the Mediterranean region. Nature 226, 239–241. McKenzie, D.P., 1972. Active tectonics of the Mediterranean region. Geophys. J. R. Astron. Soc. 30 (2), 109–185. Meade, B., Hager, B., Reilinger, R., 2002. Estimates of seismic potential in the Marmara region from block models of secular deformation constrained by GPS measurements. Bull. Seismol. Soc. Am. 92 (1), 208–215. Pınar, N., 1953. Preliminary Note on the Earthquake of Yenice Gönen, Turkey, March 18, 1953. Bull. Seismol. Soc. Am., vol. 43, pp. 307–310. Reilinger, R.E., McClusky, S.C., Oral, M.B., King, R.W., Toksoz, M.N., Barka, A.A., Kinik, I., Lenk, O., Sanli, I., 1997. Global positioning system measurements of present
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