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Semih Ergintav - One of the best experts on this subject based on the ideXlab platform.
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Interseismic strain build-up on the submarine North Anatolian Fault offshore Istanbul
Nature Communications, 2019Co-Authors: Dietrich Lange, Pierre Sakic, Valerie Ballu, Jean-yves Royer, Florian Petersen, Ziyadin Cakir, Heidrun Kopp, Pierre Henry, Jörg Bialas, Semih ErgintavAbstract:Using offshore geodetic observations, we show that a segment of the North Anatolian Fault in the central Sea of Marmara is locked and therefore accumulating strain. The strain accumulation along this Fault segment was previously extrapolated from onshore observations or inferred from the absence of seismicity, but both methods could not distinguish between fully locked or fully creeping Fault behavior. A network of acoustic transponders measured crustal deformation with mm-precision on the seafloor for 2.5 years and did not detect any significant Fault displacement. Absence of deformation together with sparse seismicity monitored by ocean bottom seismometers indicates complete Fault locking to at least 3 km depth and presumably into the crystalline basement. The slip-deficit of at least 4 m since the last known rupture in 1766 is equivalent to an earthquake of magnitude 7.1 to 7.4 in the Sea of Marmara offshore metropolitan Istanbul.
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surface creep on the North Anatolian Fault at ismetpasa turkey 1944 2016
Journal of Geophysical Research, 2016Co-Authors: Roger Bilham, Semih Ergintav, Ziyadin Cakir, Haluk Ozener, Asli Dogru, D Mencin, Alkut Aytun, Bahadir Aktug, Onur YilmazAbstract:We re-evaluate the 72 year history of surface slip on the North Anatolian Fault at Ismetpasa since the Mw = 7.4 1944 Bolu/Gerede earthquake. A revised analysis of published observations suggests that days after the earthquake the Fault had been offset by 3.7 m, and 6 years later by an additional 0.74 m. Creep was first recognized on the Fault in 1969 as a 0.13 m offset of a wall constructed in 1957 that now (2016) has been offset by 0.52 m. A carbon-rod creep-meter operated across the Fault in the past two years confirms results from an invar-wire creep-meter operated 1982-1991 that surface slip is episodic. Months of Fault inactivity are interrupted by slow slip (≤10 µm/day) or multiple creep events with cumulative amplitudes of 2-10 mm, durations of several weeks, and with slip-rates briefly exceeding >2.5 mm/hour. Creep events accommodate 80% of the surface slip and individually release ≈ 10-6 shear-strain on the flanks of the uppermost 3-7 km of the Fault. GPS and InSAR methods yield a current Fault slip rate of 7.6 ± 1 mm/yr suggesting that creep-meters incompletely sample the full width of the surface shear zone. The slip rate has slowed from >10 mm/yr in 1969 to 6.1 mm/year at present, 4.65 mm/yr of which appears to be due to steady interseismic creep driven by plate boundary stressing rates. We calculate that a further 1 m of aseismic surface slip will precede the next major earthquake on the Fault assuming a ≈ 260 year mainshock recurrence interval on this segment.
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No significant steady state surface creep along the North Anatolian Fault offshore Istanbul: Results of 6 months of seafloor acoustic ranging
Geophysical Research Letters, 2016Co-Authors: Pierre Sakic, Helen Piété, Valerie Ballu, Jean-yves Royer, Heidrunn Kopp, Dietrich Lange, Florian Petersen, M. Sinan Özeren, Semih Ergintav, Louis GeliAbstract:The submarine Istanbul-Silivri Fault segment, within 15 km of Istanbul, is the only portion of the North Anatolian Fault that has not ruptured in the last 250 years. We report first results of a seafloor acoustic ranging experiment to quantify current horizontal deformation along this segment and assess whether the segment is creeping aseismically or accumulating stress to be released in a future event. Ten transponders were installed to monitor length variations along 15 baselines. A joint least squares inversion for across-Fault baseline changes, accounting for sound speed drift at each transponder, precludes Fault displacement rates larger than a few millimeters per year during the 6 month observation period. Forward modeling shows that the data better fit a locked state or a very moderate surface creep—less than 6 mm/yr compared to a far-field slip rate of over 20 mm/yr—suggesting that the Fault segment is currently accumulating stress.
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crustal deformation and kinematics of the eastern part of the North Anatolian Fault zone turkey from gps measurements
Tectonophysics, 2012Co-Authors: Orhan Tatar, Semih Ergintav, Ziyadin Cakir, Fatih Poyraz, H Gursoy, Zafer Akpinar, Fikret Kocbulut, Fikret Sezen, Tarik Turk, Kemal Ozgur HastaogluAbstract:Abstract The North Anatolian Fault Zone (NAFZ) is a 1200 km long dextral strike-slip Fault zone forming the boundary between the Eurasian and Anatolian plates. It extends from the Gulf of Saros (North Aegean) in the west to the town of Karliova in eastern Turkey. Although there have been numerous geodetic studies concerning the crustal deformation, velocity field and the slip rate of the NAFZ along its western and central segments, geodetic observations along the eastern section of the NAFZ are sparse. In order to investigate the GPS velocities and the slip rate along the eastern part of the NAFZ, a dense GPS network consisting of 36 benchmarks was installed between Tokat and Erzincan on both sides of the Fault zone and measured from 2006 to 2008. Measurement results indicate that the slip rate of the NAFZ increases westwards within about 400 km from 16.3 ± 2.3 mm/year to 24.0 ± 2.9 mm/year, in consistence with the observation that the Anatolian block is being pulled by the Hellenic trench rather than being pushed by the Arabian plate as a result of continental collision between the Arabian and Eurasian plates in eastern Turkey since late Miocene. Modelling the GPS velocities shows that Fault locking depth increases also in the same direction from 8.1 ± 3.3 km to 12.8 ± 3.9 km. Slip rate decreases as moving off the Hellenic trench. An average slip rate of 20.1 ± 2.4 mm/year and a locking depth of 12.5 ± 3.5 km are also estimated for the entire study area by using all of the GPS measurements obtained in this study. The GPS velocities are in good agreement with the kinematic models created by paleomagnetic studies in the region and complete the overall picture.
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determining and modeling tectonic movements along the central part of the North Anatolian Fault turkey using geodetic measurements
Journal of Geodynamics, 2011Co-Authors: Hakan Yavasoglu, Ziyadin Cakir, Okan Tuysuz, Ergin Tari, Semih ErgintavAbstract:Abstract The North Anatolian Fault (NAF), which extends from Karliova in Eastern Turkey to the Gulf of Saros in the Northern Aegean Sea, is one of the longest active strike-slip Faults in the world with a length of about 1500 km. Within the North Anatolian Shear Zone (NASZ) there are long splays off the main trunk of the NAF veering towards the interior parts of Anatolia. Although the whole shear zone is still seismically active, the major seismicity is concentrated along the main branch of the NAF. Splays of the NAF dissect the shear zone into different continental blocks. The largest splay of the NAF was selected to analyze the distribution of movements between the Faults delimiting these blocks. Four years of GPS measurements and modeling results indicate that the differential motion between the Anatolian collage and the Eurasian plate along the central part of the NAF is partitioned between Fault splays and varies between 18.7 ± 1.6 and 21.5 ± 2.1 mm/yr with the main branch taking ∼90% of the motion.
Ziyadin Cakir - One of the best experts on this subject based on the ideXlab platform.
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Interseismic strain build-up on the submarine North Anatolian Fault offshore Istanbul
Nature Communications, 2019Co-Authors: Dietrich Lange, Pierre Sakic, Valerie Ballu, Jean-yves Royer, Florian Petersen, Ziyadin Cakir, Heidrun Kopp, Pierre Henry, Jörg Bialas, Semih ErgintavAbstract:Using offshore geodetic observations, we show that a segment of the North Anatolian Fault in the central Sea of Marmara is locked and therefore accumulating strain. The strain accumulation along this Fault segment was previously extrapolated from onshore observations or inferred from the absence of seismicity, but both methods could not distinguish between fully locked or fully creeping Fault behavior. A network of acoustic transponders measured crustal deformation with mm-precision on the seafloor for 2.5 years and did not detect any significant Fault displacement. Absence of deformation together with sparse seismicity monitored by ocean bottom seismometers indicates complete Fault locking to at least 3 km depth and presumably into the crystalline basement. The slip-deficit of at least 4 m since the last known rupture in 1766 is equivalent to an earthquake of magnitude 7.1 to 7.4 in the Sea of Marmara offshore metropolitan Istanbul.
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quantifying the partition between seismic and aseismic deformation along creeping and locked sections of the North Anatolian Fault turkey
Pure and Applied Geophysics, 2019Co-Authors: Maor Kaduri, Cecile Lasserre, Ziyadin Cakir, Jeanpierre Gratier, Francois RenardAbstract:Shallow aseismic creep is a key deformation component along plate boundaries that contributes to the energy budget during the seismic cycle. Several major active continental Faults show spatial alternation of creeping and locked sections. The present study focuses on the evaluation of the aseismic part of the total displacement along the North Anatolian Fault in Turkey. Detailed microstructural analyses of finite strain were performed using various methods, based on change of length or angle, on six representative samples collected over 32 outcrops along locked and creeping sections of the Fault. Chemical analyses were used to map mineral composition of Fault rocks and to calculate relative volume changes associated with creep. The relationship between finite strain and volume change allowed quantifying the evolution of the penetrative pressure solution cleavage mechanism of creep. In volcanic and analogous creeping rocks, finite strain measurements revealed two spatial scales of strain that correspond to the alternation of two types of shear zones, with cleavages either oblique or sub-parallel to the Fault displacement. Using geodetic and geologic data, cumulative aseismic displacement was calculated in the range 9–49% of the total 80-km displacement in the creping sections and was negligible in locked sections. The large uncertainty in the kilometer-width creeping sections was related to the difficulty of quantifying the high strain values associated with high shear displacement and for which measurement uncertainties are large. A promising way to improve such quantification would be to develop reliable statistical analysis of cleavage orientation in the field.
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the implications of Fault zone transformation on aseismic creep example of the North Anatolian Fault turkey
Journal of Geophysical Research, 2017Co-Authors: Maor Kaduri, Francois Renard, Ziyadin Cakir, Jeanpierre Gratier, Cecile LasserreAbstract:Aseismic creep is observed at surface along several segments of the North Anatolian right-lateral active Fault in Turkey, a major plate boundary between Eurasia and Anatolia. Identifying the mechanisms that control creep and their temporal and spatial change represents a major challenge for predicting the mechanical evolution of active Faults, the interplay between creep and earthquakes, and the link between short-term observations from geodesy and the long-term Fault zone evolution. We combine geological observations, laboratory analyses, and imaging techniques, shedding new light on the mechanism of Fault creep along the North Anatolian Fault (NAF) and its time-dependent change. A clear correlation is shown between shallow creep and near-surface Fault gouge composition: locked segments of the NAF are mostly composed of massive limestones without clay gouges, whereas creeping segments comprise clay gouges that contain low-friction minerals. Such Fault gouges appear to result from a progressive change of initial volcanic host rocks during their deformation. Anastomosing cleavage develops during the first stage of displacement, leading to layering, oblique at first and then subparallel to the Fault, which accommodates part of the aseismic creep by pressure solution. Soluble minerals are dissolved, leading to passive concentration of phyllosilicates in the gouges where alteration transformations by fluid flow produce low friction minerals. At the same time damage zones are fractured and fractures are sealed by carbonates. As a result, these mineralogical and structural transformations weaken the gouge and strengthen the damage zone leading to the change from diffuse to localized seismic-aseismic zones.
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surface creep on the North Anatolian Fault at ismetpasa turkey 1944 2016
Journal of Geophysical Research, 2016Co-Authors: Roger Bilham, Semih Ergintav, Ziyadin Cakir, Haluk Ozener, Asli Dogru, D Mencin, Alkut Aytun, Bahadir Aktug, Onur YilmazAbstract:We re-evaluate the 72 year history of surface slip on the North Anatolian Fault at Ismetpasa since the Mw = 7.4 1944 Bolu/Gerede earthquake. A revised analysis of published observations suggests that days after the earthquake the Fault had been offset by 3.7 m, and 6 years later by an additional 0.74 m. Creep was first recognized on the Fault in 1969 as a 0.13 m offset of a wall constructed in 1957 that now (2016) has been offset by 0.52 m. A carbon-rod creep-meter operated across the Fault in the past two years confirms results from an invar-wire creep-meter operated 1982-1991 that surface slip is episodic. Months of Fault inactivity are interrupted by slow slip (≤10 µm/day) or multiple creep events with cumulative amplitudes of 2-10 mm, durations of several weeks, and with slip-rates briefly exceeding >2.5 mm/hour. Creep events accommodate 80% of the surface slip and individually release ≈ 10-6 shear-strain on the flanks of the uppermost 3-7 km of the Fault. GPS and InSAR methods yield a current Fault slip rate of 7.6 ± 1 mm/yr suggesting that creep-meters incompletely sample the full width of the surface shear zone. The slip rate has slowed from >10 mm/yr in 1969 to 6.1 mm/year at present, 4.65 mm/yr of which appears to be due to steady interseismic creep driven by plate boundary stressing rates. We calculate that a further 1 m of aseismic surface slip will precede the next major earthquake on the Fault assuming a ≈ 260 year mainshock recurrence interval on this segment.
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an aseismic slip transient on the North Anatolian Fault
Geophysical Research Letters, 2016Co-Authors: B Rousset, Romain Jolivet, Mark Simons, Cecile Lasserre, Bryan Riel, Pietro Milillo, Ziyadin Cakir, Francois RenardAbstract:Constellations of Synthetic Aperture Radar (SAR) satellites with short repeat time acquisitions allow exploration of active Faults behavior with unprecedented temporal resolution. Along the North Anatolian Fault (NAF) in Turkey, an 80 km long section has been creeping at least since the 1944, M_w 7.3 earthquake near Ismetpasa, with a current Interferometric Synthetic Aperture Radar (InSAR)-derived average creep rate of 8 ± 3 mm/yr (i.e., a third of the NAF long-term slip rate). We use a dense set of SAR images acquired by the COSMO-SkyMed constellation to quantify the spatial distribution and temporal evolution of creep over 1 year. We identify a major burst of aseismic slip spanning 31 days with a maximum slip of 2 cm, between the surface and 4 km depth. This result shows that Fault creep along this section of the NAF does not occur at a steady rate as previously thought, highlighting a need to revise our understanding of the underlying Fault mechanics.
A Barka - One of the best experts on this subject based on the ideXlab platform.
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ground penetrating radar investigations along the North Anatolian Fault near izmit turkey constraints on the right lateral movement and slip history
Geology, 2004Co-Authors: Matthieu Ferry, Thomas K Rockwell, Mustapha Meghraoui, Jeanfrancois Girard, Ozgur Kozaci, Serdar Akyuz, A BarkaAbstract:We analyze ground-penetrating radar (GPR) profiles made across and parallel to the August 1999 earthquake ruptures of the North Anatolian Fault in Turkey. The profiles document cumulative right-lateral offset of stream channels and the successive Faulting of a medieval (Ottoman) canal. The dominance of fine sand to coarse gravel in the sections imaged allows for reasonably deep penetration, and processed radar signals clearly image visible reflectors within the uppermost 5 m. Near Kosekoy, buried fluvial-channel deposits, exposed in some trenches dug to determine paleoseismicity, are also visible on profiles and show a maximum 6.7–7.4 m of lateral displacement. Younger channel units display 4.5–4.9 m of right-lateral displacement at 2–3 m depth and show that the penultimate rupture along the Izmit segment produced a similar amount of displacement as in 1999. At the Ottoman canal site, GPR profiles complement a trench study and provide consistent results showing the occurrence of three Faulting events after A.D. 1591, the date of canal construction. This study demonstrates that the use of GPR method in paleoseismology contributes to better identification of cumulative slip along active Faults.
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paleoseismic evidence of characteristic slip on the western segment of the North Anatolian Fault turkey
Bulletin of the Seismological Society of America, 2003Co-Authors: Yann Klinger, A Barka, Erhan Altunel, Aron J Meltzner, Kerry Sieh, Ahmet M Akoglu, T E Dawson, Tania Gonzalez, Thomas K RockwellAbstract:We have conducted a paleoseismic investigation of serial Fault rupture at one site along the 110-km rupture of the North Anatolian Fault that produced the Mw 7.4 earthquake of 17 August 1999. The benefit of using a recent rupture to compare serial ruptures lies in the fact that the location, magnitude, and slip vector of the most recent event are all very well documented. We wished to determine whether or not the previous few ruptures of the Fault were similar to the recent one. We chose a site at a step-over between two major strike-slip traces, where the principal Fault is a normal Fault. Our two excavations across the 1999 rupture reveal fluvial sands and gravels with two colluvial wedges related to previous earthquakes. Each wedge is about 0.8 m thick. Considering the processes of collapse and subsequent diffusion that are responsible for the formation of a colluvial wedge, we suggest that the two paleoscarps were similar in height to the 1999 scarp. This similarity supports the concept of characteristic slip, at least for this location along the Fault. Accelerator mass spectrometry (AMS) radiocarbon dates of 16 charcoal samples are consistent with the interpretation that these two paleoscarps formed during large historical events in 1509 and 1719. If this is correct, the most recent three ruptures at the site have occurred at 210- and 280-year intervals.
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morphology displacement and slip rates along the North Anatolian Fault turkey
Journal of Geophysical Research, 2002Co-Authors: Rolando Armijo, Geoffrey King, Bertrand Meyer, Aurelia Hubertferrari, A BarkaAbstract:[1] Geological and geomorphological offsets at different scales are used to constrain the localization of deformation, total displacement, and slip rates over various timescales along the central and eastern North Anatolian Fault (NAF) in Turkey. The NAF total displacement is reevaluated using large rivers valleys (80 ± 15 km) and structural markers (Pontide Suture, 85 ± 25 km; Tosya-Vezirkopru basins, 80 ± 10 km). These suggest a Neogene slip rate of 6.5 mm/yr over 13 Myr. The river network morphology shows offsets at a range of scales (20 m to 14 km) across the main Fault trace and is also used to estimate the degree to which deformation is localized. At a smaller scale the morphology associated with small rivers is offset by 200 m along the NAF. The age of these features can be correlated with the Holocene deglaciation and a slip rate of 18 ± 3.5 mm/yr is determined. This is consistent with a rate of 18 ± 5 mm/yr deduced independently from the 14C dating of stream terrace offsets. Over the short term, GPS data gives a similar rate of 22 ± 3 mm/yr. All our results tend to show that most of the deformation between the Anatolian and Eurasian lithospheric plates has been accommodated along, or very close to, the active trace of the NAF. The difference between the Neogene and the Holocene slip rate may be due to the recent establishment of the current plate geometry after the creation of the NAF.
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surface rupture and slip distribution of the 12 november 1999 duzce earthquake m 7 1 North Anatolian Fault bolu turkey
Bulletin of the Seismological Society of America, 2002Co-Authors: Husnu Serdar Akyuz, Bertrand Meyer, A Barka, Ross D Hartleb, Erhan Altunel, Gursel Sunal, Rolando ArmijoAbstract:The 12 November 1999 earthquake ( M 7.1) occurred on the Duzce Fault, a splay of the North Anatolian Fault in the Bolu basin approximately three months after the 17 August 1999 ( M 7.4) earthquake. The surface rupture was 40 km long, and the maximum right-lateral offset was 500 ± 5 cm, averaging 300 cm. The 9 km of the westernmost part of the rupture along the southern margin of the Eften Lake had a 350-cm maximum vertical displacement (normal Faulting), some of which was already ruptured during the 17 August 1999 event with few tens of centimeters. The surface rupture has a generally simple narrow deformation zone of 0.5-5 m, however, in some places, it widens to 50 m. Transtensional and transpressional structures were observed within releasing and restraining step-over areas respectively. The larger dextral offsets on some streams indicate previous events. The dextral slip measurements along the rupture reflect a symmetric distribution. The eastern connection of this rupture zone with the main trace of North Anatolian Fault remains unclear because the Bakacak and Elmalik Fault, which are connecting Faults, had no surface rupture. Manuscript received 14 November 2000.
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the surface rupture and slip distribution of the 17 august 1999 izmit earthquake m 7 4 North Anatolian Fault
Bulletin of the Seismological Society of America, 2002Co-Authors: A Barka, Rolando Armijo, Bertrand Meyer, Ziyadin Cakir, Baris Yerli, Husnu Serdar Akyuz, Erhan Altunel, Gursel Sunal, Aynur Dikbas, J B De ChabalierAbstract:The 17 August 1999 Izmit earthquake occurred on the Northern strand of the North Anatolian Fault zone. The earthquake is associated with a 145-km-long surface rupture that extends from southwest of Duzce in the east to west of Hersek delta in the west. Detailed mapping of the surface rupture shows that it consists of five segments separated by releasing step-overs; herein named the Hersek, Karamursel-Golcuk, Izmit-Sapanca Lake, Sapanca-Akyazi, and Karadere segments from west to east, respectively. The Hersek segment, which cuts the tip of a large delta plain in the western end of the rupture zone, has an orientation of N80°. The N70°-80°E-trending Karamursel-Golcuk segment extends along the linear southern coasts of the Izmit Gulf between Karamursel and Golcuk and produced the 470-cm maximum displacement in Golcuk. The Northwest-southeast-striking Golcuk normal Fault between the Karamursel-Golcuk and Izmit-Sapanca segments has 2.3-m maximum vertical displacement. The maximum dextral offset along the Izmit-Sapanca Lake segment was measured to be about 3.5 m, and its trend varies between N80°E and east-west. The Sapanca-Akyazi segment trends N75°-85°W and expresses a maximum displacement of 5.2 m. The Karadere segment trends N65°E and produced up to 1.5-m maximum displacement. The Karadere and Sapanca-Akyazi segments form fan-shape or splaying ruptures near their eastern ends where the displacement also diminished.
Mustapha Meghraoui - One of the best experts on this subject based on the ideXlab platform.
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Active Fault segments along the North Anatolian Fault system in the Sea of Marmara: implication for seismic hazard
Mediterranean Geoscience Reviews, 2021Co-Authors: Luca Gasperini, Gulsen Ucarkus, Mustapha Meghraoui, Massimiliano Stucchi, Vincenzo Cedro, Alina PoloniaAbstract:A new analysis of high-resolution multibeam and seismic reflection data, collected during several oceanographic expeditions starting from 1999, allowed us to compile an updated morphotectonic map of the North Anatolian Fault below the Sea of Marmara. We reconstructed kinematics and geometries of individual Fault segments, active at the time scale of 10 ka, an interval which includes several earthquake cycles, taking as stratigraphic marker the base of the latest marine transgression. Given the high deformation rates relative to sediment supply, most active tectonic structures have a morphological expression at the seafloor, even in presence of composite Fault geometries and/or overprinting due to mass-wasting or turbidite deposits. In the frame of the right-lateral strike-slip domain characterizing the North Anatolian Fault system, three types of deformation are observed: almost pure strike-slip Faults, oriented mainly E–W; NE/SW-aligned axes of transpressive structures; NW/SE-oriented trans-tensional depressions. Fault segmentation occurs at different scales, but main segments develop along three major right-lateral oversteps, which delimit main Fault branches, from east to west: (i) the transtensive Cinarcik segment; (ii) the Central (East and West) segments; and (iii) the westernmost Tekirdag segment. A quantitative morphometric analysis of the shallow deformation patterns observed by seafloor morphology maps and high-resolution seismic reflection profiles along the entire basin allowed to determine nature and cumulative lengths of individual Fault segments. These data were used as inputs for empirical relationships, to estimate maximum expected Moment Magnitudes, obtaining values in the range of 6.8–7.4 for the Central, and 6.9–7.1 for the Cinarcik and Tekirdag segments, respectively. We discuss these findings considering analyses of historical catalogues and available paleoseismological studies for the Sea of Marmara region to formulate reliable seismic hazard scenarios.
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Paleoseismic history and slip rate along the Sapanca-Akyazi segment of the 1999 Izmit earthquake rupture (M-w=7.4) of the North Anatolian Fault (Turkey)
Tectonophysics, 2018Co-Authors: Aynur Dikbas, Cengiz Zabci, H. Serdar Akyüz, Erhan Altunel, Matthieu Ferry, Mustapha Meghraoui, Robert Langridge, Cahit Caglar YalcinerAbstract:The Sapanca-Akyazı segment (SAS) is located on western part of the North Anatolian Fault (NAF) of Turkey. It was ruptured together with four other segments during the 17th August 1999 İzmit earthquake (Mw = 7.4) which caused ~145-km-long surface rupture in the east Marmara region. We conducted geomorphological investigations and 2D–3D paleoseismic trenching at 3 different sites near the Sakarya River along the SAS to obtain new data for the timing of past earthquakes and slip rate of this section of the NAF. Detailed investigations using Ground Penetrating Radar on the western bank of the Sakarya River reveal 18.5 ± 0.5 m of right-lateral cumulative offset of an alluvial terrace dated as 850 ± 11 years BP using Optically Stimulated Luminescence. The analysis of trench data from the three different sites of the SAS indicates the occurrence of four surface rupturing past earthquakes including the 1999 İzmit earthquake. According to the radiocarbon dating, these paleo-earthquakes can be correlated with the 1719 CE, 1567 CE, and 1037 CE historical earthquakes and suggest an average recurrence period between 273 and 322 years. The total dextral offset, the age of trench units and the terrace deposits together suggest a 22 ± 3 mm/yr slip rate for this portion of the NAF.
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Paleoseismology of the North Anatolian Fault at Güzelköy (Ganos segment, Turkey): Size and recurrence time of earthquake ruptures west of the Sea of Marmara
Geochemistry Geophysics Geosystems, 2012Co-Authors: Mustapha Meghraoui, H. Serdar Akyüz, Matthieu Ferry, M. Ersen Aksoy, Aynur Dikbas, Erhan AltunelAbstract:The Ganos Fault is the westernmost segment of the North Anatolian Fault that experienced the Mw = 7.4 earthquake of 9 August 1912. The earthquake revealed 45-km-long of surface ruptures inland, trending N70 E, and 5.5 m of maximum right lateral offset near Güzelköy. The long-term deformation of the Fault is clearly expressed by several pull-apart basins and sag ponds, pressure and shutter ridges and offset streams. In parallel with detailed geomorphologic investigations, we measured co-seismic and cumulative displacements along the Fault, and selected the Güzelköy site for paleoseismology. A microtopographic survey at the site yields 10.5 0.5 m and 35.4 1.5 m cumulative lateral offsets of stream channels and geomorphologic features. Seven paleoseismic parallel and cross-Fault trenches document successive Faulting events and provide the timing of past earthquakes on the Ganos Fault segment. Radiocarbon dating of successive colluvial wedges in trench T1, and the fresh scarplet above (probably 1912 surface rupture) indicate the occurrence of three Faulting events since the 14th century. Parallel trenches (3, 5, 6 and 7) expose paleo-channels and show a cumulative right-lateral offset of 16.5 1.5 m next to the Fault, and 21.3 1.5 m total channel deflection. Radiocarbon dating of past channel units and Fault scarp-related colluvial deposits imply an average 17 +/ 5 mm/year slip rate and 323 142 years recurrence interval of large earthquakes during the last 1000 years on the Ganos Fault. The succession of past Faulting events and inferred slip rate west of the Marmara Sea provide more constraint on the long-term Faulting behavior in the seismic gap of the North Anatolian Fault and may contribute to a better seismic hazard assessment in the Istanbul region.
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palaeoseismology of the North Anatolian Fault near the marmara sea implications for Fault segmentation and seismic hazard
Geological Society London Special Publications, 2009Co-Authors: Thomas K Rockwell, Gordon G Seitz, Daniel Ragona, R M Langridge, Ersen M Aksoy, Gulsen Ucarkus, Matthieu Ferry, Aron J Meltzner, Yann Klinger, Mustapha MeghraouiAbstract:We conducted palaeoseismic studies along the North Anatolian Fault both east and west of the Marmara Sea to evaluate its recent surface rupture history in relation to the well-documented historical record of earthquakes in the region, and to assess the hazard of this major Fault to the city of Istanbul, one of the largest cities in the Middle East. Across the 1912 rupture of the Ganos strand of the North Anatolian Fault west of the Marmara Sea, we excavated 26 trenches to resolve slip and constrain the earthquake history on a channel–fan complex that crosses the Fault at a high angle. A distinctive, well-sorted fine sand channel that served as a marker unit was exposed in 21 trenches totaling over 300 m in length. Isopach mapping shows that the sand is channelized North of the Fault, and flowed as an overflow fan complex across a broad Fault scarp to the south. Realignment of the feeder channel thalweg to the fan apex required about 9±1 m of reconstruction. Study of the rupture history in several exposures demonstrates that this displacement occurred as two large events. Analysis of radiocarbon dates places the age of the sand channel as post ad 1655, so we attribute the two surface ruptures to the large regional earthquakes of 1766 and 1912. If each was similar in size, then about 4–5 m of slip can be attributed to each event, consistent with that reported for 1912 farther east. We also found evidence for two additional surface ruptures after about ad 900, which probably correspond to the large regional earthquakes of 1063 and 1344 (or 1354). These observations suggest fairly periodic occurrence of large earthquakes (RI=c. 283±113 years) for the past millennium, and a rate of c. 16 mm/a if all events experienced similar slip. We excavated six trenches at two sites along the 1999 Izmit rupture to study the past earthquake history along that segment of the North Anatolian Fault. One site, located in the township of Kosekoy east of Izmit, revealed evidence for three surface ruptures (including 1999) during the past 400 years. The other trench was sited in an Ottoman canal that was excavated (but never completed) in 1591. There is evidence for three large surface rupturing events in the upper 2 m of alluvial fill within the canal at that site, located only a few kilometres from the Kosekoy site. One of the past events is almost certainly the large earthquake of 1719, for which historical descriptions of damage are nearly identical to that of 1999. Other earthquakes that could plausibly be attributed to the other recognized rupture of the Izmit segment are the 1754, 1878 or 1894 events, all of which produced damage in the region and for which the source Faults are poorly known. Our palaeoseismic observations suggest that the Izmit segment of the North Anatolia Fault ruptures every one and a half centuries or so, consistent with the historical record for the region, although the time between ruptures may be as short as 35 years if 1754 broke the Izmit segment. Release of about 4 m of seismic slip both west and east of the Marmara Sea this past century (1912, 1999) support the contention that Istanbul is at high risk from a pending large earthquake. In that historical records suggest that the last large central Marmara Sea event occurred in 1766, there may be a similar 4 m of accumulated strain across the Marmara basin segment of the North Anatolian Fault.
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creeping along the ismetpasa section of the North Anatolian Fault western turkey rate and extent from insar
Earth and Planetary Science Letters, 2005Co-Authors: Ziyadin Cakir, Semih Ergintav, Ahmet M Akoglu, Samir Belabbes, Mustapha MeghraouiAbstract:Creeping along the North Anatolian Fault (NAF) at Ismetpasa (Turkey) was discovered some thirty years ago, about a decade after the first observations of the phenomenon along the San Andreas Fault in California. However, little is known about its lateral extent and rate. In order to study its three dimensional nature and rupture characteristics, we use Synthetic Aperture Radar Interferometry (InSAR) and elastic dislocation models compared also with field observations. Interferograms with temporal baselines ranging between 1.25 and 5 years show that the creeping section starts at the western termination of the 1943 (M=7.6) earthquake rupture. It continues about 70-km to the west, overlapping with the eastern part of the 1944 (M=7.3) earthquake rupture. Offsets along strike indicate a maximum creep rate of 11F3 mm/year near the mid point of the creeping section decreasing gradually towards the edges. Near Ismetpasa, InSAR data yield 8F3 mm/year of creep rate, consistent with recent instrumental (triangulation and creepmeter) measurements. Modeling of the InSAR and GPS data suggests that the Faultcreep occurs most probably at a shallow depth (0–7 km). Our analysis combined with previous studies suggests that creeping might have commenced following the 1944 earthquake, and thus may be a long-lasting, but transient slip episode. D 2005 Elsevier B.V. All rights reserved.
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structure controlled seismic anisotropy along the karadere duzce branch of the North Anatolian Fault revealed by shear wave splitting tomography
Earth and Planetary Science Letters, 2014Co-Authors: Haijiang Zhang, Zhigang PengAbstract:Abstract We use a three-dimensional (3D) shear-wave splitting (SWS) tomography method developed by Zhang et al. (2007) to map the spatial distribution of crustal anisotropy in the Karadere–Duzce branch of the North Anatolian Fault (NAF) in western Turkey. The input data consists of 20 751 measurements of the SWS delay times from 7856 aftershocks of the 1999 Mw 7.4 Izmit and Mw 7.1 Duzce earthquakes. The results show a continuous belt-like highly anisotropic zone along the Karadere-Duzce branch of NAF, generally ∼ 3 km wide and down to ∼ 5 km deep. The observed asymmetric pattern of anisotropy along the Karadere segment is qualitatively consistent with asymmetric damages from the unilateral eastward propagation of the Izmit rupture. Another strong anisotropy region was found near the end of the Izmit rupture zone, close to the dipping direction of the Fault segment that ruptured during the subsequent Duzce earthquake. These results are generally consistent with the shallow Fault-zone anisotropy inferred from previous studies. While the anisotropy generally becomes weaker at depth and/or outside the Fault zone, we also identify several highly anisotropic regions as deep as ∼ 10 km , primarily within the Almacik block. These isolated anisotropy regions could be explained by individual intrusive igneous rock bodies with different mineral alignment. Overall, seismic anisotropy in upper crust of the Karadere-Duzce branch of the NAF is structurally controlled.
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velocity contrast across the 1944 rupture zone of the North Anatolian Fault east of ismetpasa from analysis of teleseismic arrivals
Geophysical Research Letters, 2012Co-Authors: Y Ozakin, Yehuda Benzion, Mustafa Aktar, Hayrullah Karabulut, Zhigang PengAbstract:[1] We use differences between arrival times of teleseismic events at sets of stations crossing the North Anatolian Fault east of Ismetpasa, where shallow creep has been observed, to detect and quantify a contrast of seismic velocities across the Fault. Waveform cross correlations are utilized to calculate phase delays of P waves with respect to expected teleseismic arrivals with incident angles corresponding to the generating events. Compiled delay times associated with 121 teleseismic events indicate about 4.3% average P wave velocity contrast across the Fault over the top 36 km, with faster velocity on the North side. The estimated contrast is about 8.3% if the velocity contrast is limited to the top 18 km. The sense of velocity contrast is consistent with the overall tectonic setting and inference made for the examined Fault section based on theoretical expectations for bimaterial ruptures and observed asymmetry of rock damage across the Fault. Our data indicate lack of significant microseismicity near the Fault, suggesting that creep in the area is limited to the depth section above the seismogenic zone.
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systematic analysis of crustal anisotropy along the karadere duzce branch of the North Anatolian Fault
Geophysical Journal International, 2004Co-Authors: Zhigang Peng, Yehuda BenzionAbstract:S U M M A R Y We perform a systematic analysis of crustal anisotropy along and around the Karadere–Duzce branch of the North Anatolian Fault (NAF), which ruptured during the 1999 Mw 7.4 Izmit and Mw 7.1 Duzce earthquakes. A method consisting of an iterative grid search for the best shear wave splitting parameters in sliding time windows is applied to ∼22 000 measurements recorded in the 6-month period after the Izmit main shock. Based on objective criteria, ∼6600 measurements are assigned high quality and used for further detailed analysis. Most stations near the rupture zone have fast polarization directions that are parallel to, and change with, the nearby Fault strike. The average delay times for ray paths that propagate along the rupture zone are larger than for the other paths. These results suggest the existence of an approximately 1-km broad zone around the Karadere–Duzce branch with Fault-parallel cracks or shear fabric. However, some Fault zone (FZ) stations record bimodal or scattered polarization directions, while stations near large structural complexities (e.g. branching and offsets) show average fast polarization directions that are almost perpendicular to the local Fault strike. The average fast polarization directions from ray paths that propagate inside the Almacik block, south of the Karadere–Duzce branch, are neither parallel to the local Fault strike nor to the expected regional maximum compressive stress direction. The large overall spatial variations of the results imply that multiple structures and mechanisms contribute to the observed crustal anisotropy in our study area. Most stations do not exhibit a clear dependency of shear wave splitting delay time with increasing depth and hypocentral distance, indicating that the anisotropy is confined primarily to the top 3–4 km of the crust. Using the observed average delay time at FZ stations and assumed propagation distance of 3.5 km, we estimate the apparent crack density in the damaged shallow FZ rock to be approximately 7 per cent.