Turkish Journal of Earth Sciences (Turkish J. Earth Sci.), VÖo. l .K 2O0,Z 2A0C11I, EpTp .A 3L5.9–378. Copyright ©TÜBİTAK doi:10.3906/yer-0910-45 First published online 15 October 2010 Th e North Anatolian Fault on the Hersek Peninsula, Turkey: Its Geometry and Implications for the 1999 İzmit Earthquake Rupture Propagation ÖZGÜR KOZACI1,2, ERHAN ALTUNEL3, SCOTT LINDVALL2, CHARLIE BRANKMAN2,4 & WILLIAM LETTIS2 1 İstanbul Technical University, Eurasian Earth Sciences Institute, Maslak, TR−34469 İstanbul, Turkey 2 now at Fugro William Lettis & Associates, Inc., Walnut Creek, 94596 California, USA (E-mail: [email protected]) 3 Eskişehir Osmangazi University, Engineering Faculty, Department of Geological Engineering, TR−26040 Eskişehir, Turkey 4 now at Department of Earth & Planetary Sciences, Harvard University, Cambridge, Massachusetts, 02138, USA Received 02 November 2009; revised typescripts receipt 23 June 2010 & 04 August 2010; accepted 03 September 2010 ‘We dedicate this study to Aykut Barka who devoted his life to understanding the earthquake phenomenon. He was a brilliant scientist, a true friend and a giving advisor besides his humble personality. He will be remembered as a source of inspiration and kindness.’ Abstract: Th e western termination of the 1999 İzmit earthquake still remains as an intriguing problem for researchers and the people residing around the Sea of Marmara. Th ere have been numerous off shore mapping and modelling studies performed in the Gulf of İzmit. However, the main debate about the western termination of the 1999 İzmit surface rupture is linked to the Hersek Peninsula and corresponding fault geometry. We focused our eff orts at resolving the fault geometry on the Hersek Peninsula by applying geological mapping, geomorphic analyses, palaeoseismic trenching and geophysical surveys. Our studies reveal that the North Anatolian Fault forms a restraining stepover and did not experience surface rupture during 1999 İzmit earthquake in the vicinity of Hersek Peninsula. We tested this fault geometry with a fi nite element model in half elastic space and correlated the results successfully with the existing topography. In addition, we ran a simple Coulomb model to explain the possible cause of surface rupture termination at this specifi c location. Our studies, combined with detailed off shore bathymetry data, suggest that the restraining step of the North Anatolian Fault on the Hersek Peninsula is capable of creating an effi cient earthquake rupture barrier. Key Words: North Anatolian Fault, Hersek Peninsula, fault geometry, rupture termination, active tectonics Kuzey Anadolu Fayı’nın Hersek Deltası’ndaki Geometrisi ve 1999 İzmit Depremi Kırığının İlerlemesine Etkileri Özet: 1999 İzmit depreminin batıda sonlandığı yer araştırıcılar ve Marmara Denizi civarında yaşayanlar için önemli bir sorun oluşturmaya devam etmektedir. İzmit Körfezi’ni konu alan pek çok kıyı ötesi haritalama ve modelleme çalışmaları yapılmasına rağmen 1999 İzmit depremi yüzey kırığının sonlandığı yerle ilgili tartışmalar Hersek Deltası’na ve Kuzey Anadolu Fayı’nın buradaki geometrisine düğümlenmiştir. Bu sorunu anlamak üzere çalışmalarımız Hersek Deltası’ndaki fay geometrisini anlamamıza yardım edecek şekilde jeomorfolojik analizler, paleosismik hendek kazıları, ve jeofi zik araştırmalar üzerinde yoğunlaştırılmıştır. Çalışmalarımız Kuzey Anadolu Fayı’nın bu bölgede sıkışma oluşturan bir geometriye sahip olduğunu ve 1999 İzmit depremi sırasında yüzey kırığı meydana getirmediğini ortaya koymuştur. Yarı uzayda sonlu elemanlar yöntemiyle modellenen bu fay geometrisi çalışma alanının güncel topoğrafyası ile uyum göstermektedir. Ayrıca, basit bir Coulomb modellemesi ile yüzey kırığının neden burada sonuçlanmış olduğu açıklanmıştır. Deniz çalışmaları ile karada yaptığımız çalışmaların biraraya getirilmesi Kuzey Anadolu Fayı’nın Hersek Deltası’ında sıkışmalı bir sıçrama yaptığını ve bu fay geometrisinin etkin bir deprem kırığı engeli oluşturduğunu ortaya koymaktadır. Anahtar Sözcükler: Kuzey Anadolu Fayı, Hersek Deltası, fay geometrisi, kırık sonlanması, aktif tektonik 359 NORTH ANATOLIAN FAULT ON THE HERSEK PENINSULA Introduction that specifi c location are essential for estimating the location and potentially the magnitude of future large On August 17th 1999, the M7.4 İzmit earthquake earthquakes. Researchers (e.g., Barka & Kadinsky- struck the Marmara region of Turkey causing much Cade 1988; Stein et al. 1997; Wesnousky 2008) have devastation. Th e İzmit earthquake is the seventh convincingly demonstrated that fault geometry and surface rupturing, large-magnitude earthquake in Coulomb stress loading can signifi cantly aff ect the a westward migrating earthquake sequence on the initiation point of the next large earthquake on a fault North Anatolian fault (NAF) during the 20th century system. Furthermore, it has been noted that rupture (e.g., Barka et al. 2000, Figure 1a). Th e section of end points usually coincide with discontinuities on the NAF within the Sea of Marmara remains as a faults, such as stepovers (e.g., Segal & Pollard 1980; seismic gap between the 1912 Saros and 1999 İzmit Sibson 1985). Th us, gaining insights into the western earthquake ruptures and the probability of a surface extent of the 1999 İzmit earthquake rupture is rupturing earthquake event is heightened for this essential to estimate the magnitude of the expected region (e.g., Parsons 2004). Th e ~1500-km-long Marmara earthquake. Th e Hersek Peninsula is central dextral transform NAF is one of the major tectonic to the debate on the western termination of the 1999 structures of Anatolia, accommodating ~90% of surface rupture because it is the westernmost locality the deformation between the Eurasian Plate and where the NAF can be observed directly before it Anatolian Block (McClusky et al. 2000; Reilinger et enters the Sea of Marmara (Figure 1b). Th is paper al. 2006). During the İzmit earthquake, four segments aims to describe the geometry of the NAF on the (Karadere, Sakarya, Sapanca, and Gölcük) of the Hersek Peninsula and discusses its implications on NAF experienced surface rupture with right-lateral the fault rupture of the 1999 İzmit earthquake. displacements of up to fi ve metres. Th e ~126-km- long surface rupture terminated near Gölyaka in In this study we employed a comprehensive, the east (Figure 1b), but the western termination of multi-technique approach on the Hersek Peninsula. the İzmit earthquake is more uncertain since it lies Specifi cally, we performed geomorphic analyses, off shore in İzmit Bay. According to some geodetic geological mapping, palaeoseismic trenching, models (i.e. Wright et al. 2001; Reilinger et al. 2000; geophysical surveying, modelling of deformation in Bürgmann et al. 2002) and seismicity analysis (i.e. half-elastic space with fi nite elements and Coulomb Pınar et al. 2001) it was suggested that the 1999 stress change modelling. We also combined our on surface rupture extended 10–30 km west of the land results with the existing off shore data in order Hersek Peninsula. Off shore studies within the Gulf to present a complete fault model for the Hersek of İzmit demonstrated the presence of underwater Peninsula. We then present a detailed discussion of fault scarps (Polonia et al. 2004; Cormier et al. the implications of fault geometry at our study area. 2006; Uçarkuş et al. 2008), but these were somewhat inconclusive in addressing the location of the 1999 Study Site rupture termination. A Historical Background Understanding where earthquake ruptures terminate has fundamental implications for Th e Hersek Peninsula is a triangular fan-delta with Probabilistic Seismic Hazard Analysis (PSHA) and an area of ~25 km2 in the Gulf of İzmit (Figures 1b & earthquake physics. Structural complexities along 2). Th e tip of the Hersek Peninsula extends ~5.5 km faults (i.e. asperities, stepovers, bends, and structural northward into the Gulf of İzmit creating the shortest junctions) may arrest rupture propagation and cause distance (~2.7 km) between the northern and perturbation of the state of stress on adjacent fault southern shores. Th e location and physiography of segments. Th e fi rst and most vital step is documenting the Hersek Peninsula not only allows for a shortened the characteristics (i.e. hypocentre, extent, geometry, gulf crossing but also controls the entrance to the and slip distribution) of individual ruptures. gulf and the route to İzmit (Nicomedia) and İznik Documenting earthquake rupture endpoints and (Nicaea) while providing a suitable landfall area with understanding what caused a rupture to terminate at its beaches and delta plain. Consequently it has been 360 Ö. KOZACI ET AL. 5’ 4 00 4 040BLACKSEA ar Suşehri 1Erzincan939 031 00’ tnemges eredaraK 010 km 031 00’ ka 1999). (b) Location map of the study quake. White bold lines are 1999 İzmit n of the fault geometry based on Kuşçu s rho Nik m Baeartetati 036 1943Ilgaz1942 030 30’ Adapazarı SapancaSakarya segment 030 30’ g earthquakes since 1939 (frocentre of the 17 August 1999 e Gulf of İzmit are our interpr Lake migratins the epines in th 002832 Eİstanbul 4491Bolu1999a1999b2119195767 0029 30’30 00’ E İzmitGulf ofİzmitHersek Gölcük segmentSapanca segmentKaramürsel17August 1999picenterMw 7.4e 0029 30’30 00’ (a) Simplifi ed map of the North Anatolian fault and westward area (dashed square) on LANDSAT image. Star symbol showearthquake surface rupture (from Lettis et al. 2000). Dashed liet al. (2002) bathymetry. N W S 91 04 a N W S b ure 1. 0 g Fi 5’ 4 00 4 361 NORTH ANATOLIAN FAULT ON THE HERSEK PENINSULA occupied for centuries as a strategic location in the era), baths, a cistern, and the Hersekzade Ahmed Gulf of İzmit (Supplementary fi gure 1). Paşa Mosque can still be readily observed in the vicinity of Hersek Village. Th e Hersekzade Ahmed Th e settlement on the Hersek Peninsula has Paşa Mosque experienced extensive damage only been known as various names by diff erent cultures one year aft er its construction during the great 1509 throughout history. It was known as Drepanon until earthquake. It experienced less extensive damage in 318 A.D. when Byzantine emperor Constantine other large earthquakes aff ecting the region including renamed Drepanon as Helenopolis aft er his mother the 1999 İzmit earthquake. who was born there. By 1087, the name Cibotos and/or Civetot were used by Europeans. However, with the eff ects of repetitive earthquakes and Geology/Geomorphology of the Study Site battles Helenopolis was, sometimes, called ‘Eleinou Th e Hersek Peninsula has four main geologic/ Polis’ meaning ‘the wretched town’ (Th e Catholic geomorphic units; (1) delta plain deposits, (2) marine Encyclopaedia 1910). Later in the 16th century terrace deposits, (3) beach ridge deposits, and (4) during the Ottoman Empire it was called Hersek lagoon deposits (Figure 3). aft er Hersekzade Ahmed Paşa. Today, it is still called Hersek Village. Th e oldest deltaic unit is the Upper Pleistocene Altınova formation (Chaput 1957; Akartuna 1968; Th e settlement on the Hersek Peninsula has Sakınç & Bargu 1989), which includes sand with undergone three major construction phases during widespread Ostrea shells, clayey sand, silty sand, history. Th e fi rst major construction took place aft er marl and sandy marl, and uncomformably overlies Constantine renamed Drepanon as Helenopolis. the Yalakdere and Taşköprü sandstone. Dedeler Hill, Constantine stayed in Helenopolis on the way 28 m a.s.l. (above sea level), is the most prominent back to İstanbul (Constantinople) from the Yalova geomorphic feature on the peninsula. Uplift ed thermal baths, especially during his last years. Aft er marine terraces on its fl anks indicate it is an area Constantine, especially during Justinian’s time, of active uplift . Dedeler hill is a NE–SW-trending Helenopolis gained more importance when the ridge, bounded by a steep scarp on its south-eastern gulf crossing traffi c was shift ed between here and fl ank (Figure 2) and more gentle slopes on its north- Dakibyza (Gebze). Justinian rebuilt Helenopolis by western fl ank. adding an aqueduct, a second public bath (a rare situation for the time), churches, a palace and other Th e delta is ~2–3 m a.s.l. and constitutes most of buildings (Supplementary fi gure 2). He also cleared the Hersek Peninsula (Kozacı 2002) (Figure 2). It is the entrance of the Drakon River (currently known formed by the north-fl owing Yalakdere River. Th e as Yalakdere), built bridges and widened the road headwaters of Yalakdere in the Samanlı Mountains to Nicaea (İznik). During this period the Drakon are ~480 m a.s.l. and ~17 km south of the Hersek River valley was used as the route connecting Peninsula. Recent deposition occurs in the northwest Constantinople (İstanbul), Helenopolis (Hersek) and portion of the delta (Figure 2). Nicaea (İznik). Later, in the 16th century, Hersekzade Th e youngest marine terraces are composed of Ahmed Paşa built a small harbour, 700 houses, a marine sand with loose fabric and coarse Gastropod mosque with two minarets named aft er him, two packages, which in some places uncomfortably inns, and a care house for the poor and a school of overlie the Altınova formation. Th ey are exposed Islamic theology. approximately 400–500 m inland near Hersek Many great earthquakes (Supplementary table 1) Village at an average elevation of about 1–2 m a.s.l. as well as battles throughout history aff ected the study (Figures 2 & 3). Th e middle and youngest marine site. During the palaeoseismic excavations by Witter terrace deposits overlie the oldest marine terrace et al. (2000) following the 1999 İzmit earthquake deposits with angular unconformity. Although all two destruction horizons were identifi ed within the marine terrace deposits have a similar lithology they trenches. In addition, many graves and bones were can be easily diff erentiated on aerial photographs by recovered. Th e remnants of an aqueduct (Justinian their elevation diff erence. Th e oldest marine terrace 362 Ö. KOZACI ET AL. Figure 2. Map showing the vicinity of the study area. Coloured contours are extracted from the 20X exaggerated digital elevation model (DEM) and overlaid on the aerial photo. Colour-coded contour intervals represent 5-m elevation changes. Note that Dedeler Hill has a NE–SW-trending elongated shape located at the north of the peninsula with an elevation of 28 m (a.s.l.). Th e delta morphology with its active and passive lobes became easily recognized as a result of using 1/1000 scale survey data. Trench locations are shown as yellow lines (T4, T5, T6…). Seismic refl ection profi le location is shown as white bold line (SRP). Very Low Frequency-Electromagnetic profi le locations are shown as a white box (VLF). Previous palaeoseismic study site by Witter et al. (2000) is shown as a yellow box (1999). Dashed white box shows the area of Figure 3 and yellow box north of Hersek Lagoon shows the location of Figure 4. Th e DEM was created using 1/1000 scale topographic survey of T.C. İller Bankası. 363 NORTH ANATOLIAN FAULT ON THE HERSEK PENINSULA deposits, about 5–6 metres thick and 10–15 m a.s.l, across a south-facing scarp forming the southern fl ank represent the shore facies with sand lenses and local of Dedeler Hill and the shore of the lagoon (Figures Ostrea rich zones. 2 & 4). Trench T-10 was excavated as a series of short trenches down the southern fl ank of Dedeler Hill Beach ridges of well-rounded pebbly sands (Figure 4). It exposed a marine terrace that abruptly are well exposed west of Hersek Village. Modern thickened and a drop of the abrasion platform, most rounded pebbly beach sand is well exposed on both probably indicative of fault deformation. Strands of the east and west shores of the Hersek Peninsula. the North Anatolian fault and related deformation Modern basin deposits and tidal marsh is composed were exposed in Trenches T-12, T-14, and T-16. of sandy silts and can be observed around Hersek Trench T-15 was excavated perpendicular to T-16 Lagoon (Figure 3). and parallel to the NAF (Figure 4), and exposed secondary strands of the NAF at this locality. Th ere Palaeoseismic Trenching was no compelling evidence of deformation within trench T-17. Following the 17 August 1999 İzmit earthquake, Witter et al. (2000) excavated several palaeoseismic trenches ~250 m northwest of the Hersek Lagoon Trench T-12 (Figure 2) in an eff ort to document the rupture Trench T-12 was excavated across a N70°E-trending history of the North Anatolian Fault on the Hersek dilatational crack that was formed during the 17 Peninsula. However, this trench site unearthed August 1999 İzmit earthquake in south of Dedeler remnants of an ancient settlement (Witter et al. Hill (Figures 4 & 5a, b). Trench T-12 is 16 metres long, 2000). Walls, foundations, clay water pipes, graves, 1.5 metres wide and 2.5 metres deep, and exposes bone fragments, and evidence of destruction were the North Anatolian fault at station eight. Th e fault documented during these excavations and the site strikes N70°E with a near vertical-dip and extends was abandoned. to the surface (Figures 5b, c & 6). South-dipping During the summer of 2000, we performed (30°), shell-rich units south of the fault and massive additional palaeoseismic trenching in two diff erent clay with sand and gravel are juxtaposed along the locations on the Hersek Peninsula (Figure 2). Th e main fault. Secondary deformation is expressed as a N65°W-trending near-vertical fi ssure at station two. fi rst set of trenches was located across the tonal Th e tilting of the units south of the fault indicates and vegetation lineaments that were mapped on north-side-up deformation. the delta plain as a result of our aerial photography interpretations. We excavated six, approximately north–south-oriented slot trenches (T-4, T-5, T-6, Trench T-14 T-7, T-8, and T-9) on the delta plain west of the Trench T-14, 22 metres long, 1.5 metres wide, and Witter et al. (2000) site (Figure 2). Th e total length approximately 2 metres deep, was excavated east of of these 1.5-m-wide trenches is ~604 m, with depths trench T-12 (Figure 4). Th e fault zone is exposed ranging between 1 to 2.2 metres, depending on between stations six and seven with an orientation ground water conditions and trench wall stability. Th e of N70°E. Marine terrace deposits and fl uvial trenches located on the delta plain exposed laterally units are juxtaposed along the fault zone (Figure continuous and undeformed strata consisting of 7a). Units south of the fault zone dip gently to the predominantly marine sand overlying silty sand, south consistent with T-12 stratigraphy (Figure 7b). sand, and clay of deltaic and lagoonal origin, but no Radiocarbon samples T14-6, T14-9, and T14-14 faults were exposed. Nevertheless, these trenches yielded calibrated (2-sigma) ages of 2215 (+133,-65) provide a spatial constraint for the fault locations on ybp (years before present), 1562 (+129,-39) ybp, and the delta plain. 3785 (+174,-93) ybp, respectively. Th ese ages indicate Th e second set of palaeoseismic trenches (T-10, faults in the trench have experienced recurrent late T-12, T-14, T-15, T-16 and T-17) were excavated Holocene ruptures. 364 Ö. KOZACI ET AL. N Qhb W E Qhpk S Qhb Qmt 1 Gulf of İ zmit Qmt 3 Qhpk Qmt 1 Qpu Qhp Qhpk Qmt2 T10 T10Qmt2 Qmt 1 Hersek Lagoon North Anatolian FQauhlat Qhb 0 1 km Explanations Qmt middle marine terrace Qhpk modern beach sand 2 Qhb modern basin and tidal marsh Qmt3 oldest marine terrace Qhp Holocene beach ridge deposits Qpu PleistoceneAltı nova f ormation terrace riser Qha Holocene alluvium Qmt young marine terrace drainage system 1 Figure 3. Geomorphic and geologic map of the Hersek Peninsula. Trench T-16 N Trench T-16, 27 m long, 1.5 m wide, with its deepest W E T-14 S T-17 section reaching 2.2 metres in depth, is located between trenches T-12 and T-14 (Figure 4). Th e T-16 N680E fault zone was observed between stations zero and eight (Figure 8a, b). A vertical fault juxtaposes T-12a horizontal units in the south against north dipping T-15 units in the north at station 0.5. Th e main fault zone, however, is oriented ~N65°E and exposed between HersekLagoon stations fi ve and eight. Th is north-dipping reverse fractures T-12b fault is accompanied with almost vertical antithetic deformation around station seven. Furthermore, the 0 30m stratigraphic units north of the main fault zone are Figure 4. Detailed map showing trench locations (T12, T14, folded and uplift ed as a result of transpression in this T15, T16, and T17) and mapped fault traces on the area. Radiocarbon samples T16-1, T16-2, and T16- south-facing scarp of Dedeler Hill. 11 yielded calibrated (2-sigma) ages of 6662 (+117,- 365 NORTH ANATOLIAN FAULT ON THE HERSEK PENINSULA Fault: N70 °E a c 5 e r u g i F c b Figure 5. (a) A fracture formed during the August 1999 earthquake. (b) Two diff erent units are juxtaposed on both sides of the North Anatolian fault in Trench T-12. (c) Close-up view of the fault on the western wall of the trench. 164) ybp, 6131 (+146,-139) ybp, and 5922 (+68,- Th ese results suggest that units north of the fault zone 152) ybp, respectively. Th e ~6.6 ka-old T16-1 was did not override the units south of the fault as a result recovered from marine terrace deposits (Unit K). Th e of reverse faulting until ~5.9 ka years before present. ~6.1 ka-old T16-2A, however, was recovered from a Th e trench exposures provided direct large anthropologic excavation (Unit L) cutting and confi rmation of the location of fault strands of the postdating units F, I, K, and J. Th ese dates suggest NAF and demonstrated that the style of deformation that the marine terrace deposits emerged above sea (right-lateral with a considerable north-side-up level some time between ~6.6 and 6.1 ka years before reverse component) is consistent with the long-term present. Th e units north of the fault zone are older style of deformation produced from repeated surface than the buried soil horizon (Unit D) south of the rupturing earthquakes refl ected in the uplift and tilt fault zone, where Sample T16-11 was recovered. of Dedeler Hill. 366 Ö. KOZACI ET AL. T-12a S N 0 A F m F A root carbonate lining B ? F contactF F ? C carbonate D D cloinnitnagct F 2 fissure N65ºW, sub-vertical E FAULTZONE N70ºE, sub-vertical 0 2 4 6 8 10 12 14 16 m A very coarse shell hash; minor sand minor amount of recrystalized fibrous material, weakly cemented; localized alterations B medium coarse shell hash to shell rich zone; upper 20 cm of unit contains fewer shell fragments and greater clay content C medium coarse shell to shell rich zone; upper 30-40 cm of zone contains very few shells, fine sand to silty sand, weakly cemented D medium coarse shell hash and some sand, fining upwards, fine sand to silty sand matrix supported E thin lens of fine sand; no shell fragments F clay (bedrock) interbedded with sand, gravel, cobbles; clay is massive, mottled; sands range from fine to well sorted and well Figure 6. Log of trench T-12 (western wall). Geophysical Surveys plots and demonstrate a structural anomaly between metres 50 and 70, in agreement with the observed Seismic refl ection and Very Low Frequency – Electro deformation on the seismic refl ection profi le (Figure Magnetometer (VLF-EM) surveys were performed 10). on the delta plain in order to locate the westward continuation of the North Anatolian Fault (Figure 2). Th e north–south-oriented, 650-m-long seismic Model refl ection profi le is located ~600 m west of the lagoon Combination of our palaeoseismic investigations on (see Figure 2). A sledge hammer was used as the energy Hersek Peninsula and off shore geophysical surveys source. A 12-channel recording system was used with (Kuşçu et al. 2002 and Cormier et al. 2006) revealed fi ve-metre geophone spacing. Interpretation of the a left -stepping geometry for the North Anatolian low-fold stacked profi le indicates the presence of a Fault (Figure 11). As a further test, we utilized fi nite discontinuity 200 metres north of the southern end element modelling in half elastic space for comparing of the seismic profi le (Figure 9). the resultant deformation of this fault geometry VLF-EM surveys, which have been successfully with the present day geomorphology (Figure 12). In used for non-mineralized shallow fault zone addition, a simple Coulomb model (Figure 13) was investigations (e.g., Jeng et al. 2004), were focused employed to provide a plausible physical explanation on the area of deformation in seismic refl ection data on how this restraining stepover might have aff ected (Figure 2). Four parallel, 90-metre-long profi les were the 1999 rupture propagation. performed fi ve metres apart in order to confi rm this deformation both laterally and vertically. Data were Finite Element Modelling in Half Elastic Space collected using an ENVI Scintrex VLF instrument with 2 metre intervals. Th e in-phase (IP), out- We tested the fault geometry documented during of-phase (OP), and TILT values were measured our fi eld studies by using fi nite element modelling in simultaneously in three diff erent frequencies between half-elastic space (Figure 12). Coulomb 2.0 (King et 15 kHz to 30 kHz (16.0, 23.4, and 26.8 kHz). All al. 1994 and Toda et al. 1998) was used to correlate measurements were stacked into three dimensional the modelled deformation patterns of various fault 367 NORTH ANATOLIAN FAULT ON THE HERSEK PENINSULA Trench T-14 S C14-T14/9 N C14-T14/6 C14-T14/14 m A1 0 A2 E A2 B F H H F D C D G F F 2 a 0 2 4 6 8 10 12 14 16 18 20 22 m A 1 Ahorizon,similartoA2butincludessomesilt b A 2 claywithsandandgravel,organicrich B sandy clay to clayey sand with gravel, many gravel clasts with diameters up to 3 cm; few tile fragments, weakly disseminated carbonate concentrated along roots andpores C similar to unit B but no carbonate concentration; fewer and smaller tile fragments; amount of sand increases towardsthebottomoftheunit D terrace deposits composed of gravelly sand to locally clayey sand; upper contact is formed by well-rounded cobbles with diameters up to 8 cm; common shell fragments E palaeo-soil;sandygravelwithroundedclastsupto1cmin diameter, common shell fragments, weakly disseminated carbonatealongtherootsandpores F marineterracedepositscomposedofinterbeddedmedium to very coarse sand and fine gravel lenses; common to manyshellfragmentsconcentratedalongbeds G clay,gravelyclay,gravelysandandclayinterbedding H palaeo-trenchesbyhumanactivity charcoalsamplesC14-T14/6C14-T14/9C14-T14/14 Figure 7. (a) Photo showing two diff erent units (white and black arrow heads) juxtaposing both sides of the fault (red arrow). (b) Log of trench T-14 (western wall). geometries with the current morphology of the same fault parameters were applied: 1 m of dextral Hersek Peninsula. We ran diff erent models with and 0.3 m vertical slip for the segments to the east of various plausible fault geometries (such as right the peninsula and on the peninsula. Th ese values are stepping, left stepping, overlapping, no overlap) both compatible with the InSAR inversions (please see determined by onshore and off shore studies (see discussions for details) and a potential segmentation online data repository for results). In all models the boundary-type deformation. Assuming that the fault 368