East Anatolian Fault System Research Articles

When did the Dead Sea fault become a transform?

This study re-evaluates the ~20 Myr development of the Dead Sea Fault System (DSFS) and its tectonic definition as a transform plate boundary. The DSFS conveys sinistral displacement between the Arabian-Sinai plates: ~105 km along its ~400 km-long southern segment (Gulf of Aqaba-Eilat to the Hula basin); ~90 km and 4–16 km along the central and northern segments (~190 km long each, across Lebanon, western Syria, and southern Turkey). A review of previous studies, combined with new seismological data analysis, associates the northward displacement decline with obstacles along the DSFS propagation path. During the Miocene, DSFS propagated up to the NW-trending Irbid rift (1st obstacle) and splayed NW towards the Mediterranean and NE along the Late Cretaceous Palmyra fold-thrust belt (2nd obstacle). Its reactivation uplifted the Hermon and the Anti-Lebanon mountain ranges. Northward DSFS propagation into the cold and rigid Aleppo plateau lithosphere (3rd obstacle) was stalled until the early Pliocene (~5 Ma), when volcanism and ongoing regional tectonic forcing enabled the DSFS to shift to the Yammouneh fault and rupture through the Missyaf-Ghab branch farther north (central and northern segments, respectively). During the Pleistocene-recent, connection of the DSFS with the ophiolite belt and East Anatolian Fault System (EAFS) along the Bitlis suture zone (4th obstacle) has not yet been established. Seismological data show a clear separation between the EAFS and the DSFS, while seismicity is scattered across the Aleppo plateau and the central and northern DSFS segments. In contrast, seismicity is localized along the southern DSFS segment. Our findings suggest that, at present, the DSFS has still not made a structural, seismologic, and tectonic connection with the EAFS. Hence, we redefine the DSFS as a pre-transform and suggest its interaction with the EAFS is a world-class example of a fault-fault-fault triple junction in the making.

Seismic variations before Eastern Anatolian catastrophic events in February 2023

AbstractThe East Anatolian Fault System has been intensively studied over the years due to its potential to generate strong earthquakes and the high exposure of the economy and population in the region. This interest intensified even more after the strong earthquakes in the area at the beginning of February 2023, leading to a focused search for features and precursors that might suggest such an upcoming event. We analyze certain characteristics of seismicity within the East Anatolian Fault System before the earthquakes of February 6, 2023, with magnitudes Mw = 7.8 and Mw = 7.5, over the time period between 1983 and 2022. The earthquake catalog from January 1983 to September 2023, created by Turkish Bogazici University KOERI, is used. Processing of the data is performed by the ZMAP 7.1 software used in the MATLAB environment. Events with a magnitude greater than 2.5 are considered in four time periods: 1983–1992, 1993–2002, 2003–2012, and 2013–2022, totaling 29,346 events. The b-value of the magnitude-frequency distribution of earthquakes (slope of the recurrence graph) is determined; the parameter β, indicative of the increase or decrease in the rate of anomalous seismicity, and parameter Z, associated with anomalous seismic quiescence, is evaluated. A significant decrease in the value of b (from 1.07 to 0.84) is observed when comparing the two periods (2013–2017/2018–2022), indicating accumulated stress in the Earth’s crust. Furthermore, the Z parameter analysis for the period July 2021 to December 2022 shows evidence of relative seismic quiet in the examined area compared to the period from January 2020 to the end of June 2021. Those results suggest that the spatiotemporal variations of the studied seismic parameters could serve as predictors of the two very strong seismic events in the southern part of the Eastern Anatolian region of Turkey.

Identification of Source Faults of Large Earthquakes in the Turkey‐Syria Border Region Between 1000 CE and the Present, and Their Relevance for the 2023 Mw 7.8 Pazarcık Earthquake

AbstractThe 6 February 2023, Mw 7.8 Pazarcık earthquake in the Turkey‐Syria border region raises the question of whether such a large earthquake could have been foreseen, as well as what is the maximum possible magnitude (Mmax) of earthquakes on the East Anatolian Fault (EAF) system and on continental transform faults in general. To answer such questions, knowledge of past earthquakes and of their causative faults is necessary. Here, we integrate data from historical seismology, paleoseismology, archeoseismology, and remote sensing to identify the likely source faults of fourteen Mw ≥ 7 earthquakes between 1000 CE and the present in the region. We find that the 2023 Pazarcık earthquake could have been foreseen in terms of location (the EAF) and timing (an earthquake along this fault was if anything overdue), but not magnitude. We hypothesize that the maximum earthquake magnitude for the EAF is in fact 8.2, that is, a single end‐to‐end rupture of the entire fault, and that the 2023 Pazarcık earthquake did not reach Mmax by a fortuitous combination of circumstances. We conclude that such unusually large events are hard to model in terms of recurrence intervals, and that seismic hazard assessment along continental transforms cannot be done on individual fault systems but must include neighboring systems as well, because they are not kinematically independent at any time scale.

Coseismic Deformation of the 2023 Türkiye Earthquake Doublet from Sentinel-1 InSAR and Implications for Earthquake Hazard

Abstract The 6 February 2023 Türkiye earthquake doublet occurred on the east Anatolian fault system, which marks the tectonic boundary between the Arabia plate and the Anatolian microplate. This earthquake doublet consists of the Mw 7.8 Pazarcik earthquake along the east Anatolian fault and the Mw 7.6 Çardak earthquake along the Savrun–Çardak fault. Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) satellite successfully imaged the surface deformation caused by this earthquake doublet. The pixel offset from cross correlation of two Synthetic Aperture Radar images complements the interferograms in mapping the surface ruptures and the near-field deformation. We inverted for a coseismic slip model in elastic half-space using the InSAR phase and the range offset data. The variance reduction of the inversion reaches ∼90%. The coseismic slip model shows that the 2023 Türkiye earthquake doublet are left-lateral strike-slip events. The peak slip is located near Nurhak in southern Türkiye along the Savrun–Çardak fault. From measuring discontinuities in the pixel offset images we found that the surface rupture length of the Pazarcik earthquake is ∼300 km and the surface rupture length of the Çardak earthquake is ∼100 km. To first order, the faults are dipping vertically. “Slip gaps” are identified by our modeling, and they might be the source regions of future large earthquakes.

The complex dynamics of the 2023 Kahramanmaraş, Turkey, Mw 7.8-7.7 earthquake doublet.

The destructive 2023 moment magnitude (Mw) 7.8-7.7 earthquake doublet ruptured multiple segments of the East Anatolian Fault system in Turkey. We integrated multiscale seismic and space-geodetic observations with multifault kinematic inversions and dynamic rupture modeling to unravel the events' complex rupture history and stress-mediated fault interactions. Our analysis reveals three subshear slip episodes during the initial Mw 7.8 earthquake with a delayed rupture initiation to the southwest. The Mw 7.7 event occurred 9 hours later with a larger slip and supershear rupture on its western branch. Mechanically consistent dynamic models accounting for fault interactions can explain the unexpected rupture paths and require a heterogeneous background stress. Our results highlight the importance of combining near- and far-field observations with data-driven and physics-based models for seismic hazard assessment.

Correlation of Ground Deformation Induced by the 6 February 2023 M7.8 and M7.5 Earthquakes in Turkey Inferred by Sentinel-2 and Critical Exposure in Gaziantep and Kahramanmaraş Cities

On 6 February 2023, an M7.8 devastating earthquake started rupturing the East Anatolian fault system in Turkey, resulting in intense shaking that lasted over a minute. A second earthquake of magnitude 7.5 struck near the city of Elbistan a few hours later. Both of these events are associated with the East Anatolian fault system. The earthquake sequence caused widespread damage and collapse of structures in densely populated areas throughout the Southern Turkey and Northern Syria regions and a very large number of human losses. This study focuses on the correlation of the ground deformation with the critical exposure of the infrastructures of Gaziantep and Kahramanmaraş cities. The estimation of the ground deformation of the affected area is achieved with the use of Copernicus Sentinel-2 products and the Normalized Cross Correlation algorithm (NCC) of image matching. The results of the East–West component show that specific sections of the region moved towards the East direction, reaching displacement measurements of 5.4 m, while other sections moved towards the West direction, reaching displacement measurements of 2.8 m. The results of the North–South component show that almost the whole affected area moved towards the North direction, with specific areas reaching displacements of 5.5 m, and a few exemptions, as some areas moved towards the South direction, with displacements reaching even 6.9 m. Regarding the cities of Kahramanmaraş and Gaziantep, their estimated movement direction is North-West and North-East, respectively, and is consistent with the movements of the Arabian and Anatolian Plates in which they are located. Important infrastructures of the study areas (education, museums, libraries, hospitals, monuments, airports, roads and railways) are superimposed on the findings, enabling us to detect the critical exposure rapidly.

Neogene volcanism in Elazig-Tunceli area (eastern Anatolia): geochronological and petrological constraints

The Elazig and Tunceli provinces in eastern Anatolia host a complex succession of Miocene-Pleistocene effusive and explosive volcanic rocks, divided into four distinct volcanic phases. The most abundant and widespread products are the calcalkaline Mazgirt volcanic rocks, characterized by wide Sr isotope variations (87Sr/86Sr ~0.7054-0.7077) and narrower 143Nd/144Nd (~0.51246-0.51260) and Pb isotopes (e.g., 206Pb/204Pb ~18.89-19.13). New 40Ar-39Ar ages indicate that Mazgirt volcanic activity occurred between ~16.3 and 15.1 Ma. The other three volcanic phases are represented by the Tunceli mildly alkaline basaltic lavas (~11.4-11.0 Ma), the Pliocene Karakocan (~4.1 Ma) and Pleistocene Elazig (~1.9-1.6 Ma) Na-alkali basaltic lavas with clear OIB-like geochemical signature.Mazgirt volcanics can be subdivided on the base of mode of emplacement into lava flows and lava domes units characterized by petrographic, chemical and isotopic differences: lava flows are calcalkaline, whereas lava domes mostly belong to a high-K calcalkaline series and are, on average, more LREE- and 87Sr-enriched. Lava domes are more porphyritic, with a phenocryst assemblage dominated by amphibole, whereas plagioclase and clinopyroxene are the most abundant phenocryst phases in lava flows, pointing out that evolution of dome magmas occurred in conditions of slightly higher pressure, favouring the crystallization of hydrous phases.The Karabakir Formation, previously reported as late Miocene- Pliocene, encloses Mazgirt volcanics and is capped by Tunceli basalts. These new age data constrain the Karabakir Formation emplacement from early to late Miocene.The evolution of this igneous activity mirrors the geodynamic framework of the region: the early-middle Miocene Mazgirt volcanics represent arc volcanism related to Eurasia-Arabia convergence. The late Miocene Tunceli basalts postdate the onset of post-collisional tectonics in Eastern Anatolia, whereas the Karakocan and Elazig volcanic rocks were emplaced after the initiation of strike-slip motion on the North Anatolian and East Anatolian Fault systems.

Structural analysis of the northern part of the East Anatolian Fault System

The East Anatolian Fault System (EAFS) is an intra-continental strike-slip fault associated with the collision of the Arabian plate with the Anatolian plate in the Alp-Himalaya system. In this study, the northern part of the EAFS, was studied. We measure more than two-hundred fault slip data (strike, dip, striation and slip sense for each fault) in eighteen different localities to make paleostress reconstruction of the related area. Several criteria are taken into consideration in order to reveal chronology of faulting such as superimposed slickenlines, age of the affected strata and syndepositional faults. Our results show three different deformation stages from the Middle Eocene to today in the study area: (1) The NW-SE extensional tectonic, oldest stage, became effective in Middle Eocene-Middle Miocene; (2) the NNE-SSW compressional tectonic become effective in Late Miocene-Early Pliocene; (3) the strike-slip tectonic, youngest stage, has been effective since Late Pliocene. The maximum compressive stress (σ1) orientation averaged around N25°E and N15°E for Stage 2 and Stage 3, respectively. This ca. 100 rotation of the maximum compressive stress (σ1) orientation may be related to the formation of the strike-slip faults concluded changing in the stress orientations between σ3 and σ2 in the Late Pliocene.

Results of the simultaneous measurements of radon around the Black Sea for seismological applications

Results of measurements of radon around of the Black Sea are shown. Radon stations in zones of active faults were placed. Simultaneous hourly measurements of soil radon in 2005 were carried out in the Sivrice Fault Zone that is a segment of East Anatolian Fault System, in the town of Tbilisi (Georgia) and in the South Russia. In 2008 simultaneously hourly measurements of soil radon were carried out in the Western Caucasus (Russia) and in the Mytilene Island (Greece). In 2013 radon in underground waters simultaneously in midday was measuring in Crete (Greece), in the Pamukkale geothermal region (Southwest Turkey) and in the Western Caucasus. Measurements of radon concentration in the points located around of the Black Sea have shown identical regularities in changes of the data. Influence of meteorological, tidal and solar factors on changes of water radon concentrations and soil radon concentrations was observed in all researches points. But this influence was insignificant. Seismological application of observed results also was considered. Various mathematical methods of definition of anomaly in the radon data during earthquakes were considered. During researches in the Black Sea region basically earthquakes with M from 2.0 up to 5.0 and in a depth about 10 km were occurred. For these earthquakes method of daily subtraction of the data of the next and previous day was used. This method has allowed solving a problem with a choice of average value. Probability up to 0.69 (number of earthquakes with radon anomalies/total number of earthquakes) of detection of radon anomalies before earthquakes was achieved applying this method. Changes of radon maps before regional earthquakes were also observed. The frequency analysis of variations of the radon data on the basis of the Wavelet analysis was carried out. Occurrence of the short periods (about 2 days) was observed during regional earthquakes.

A Fuzzy Logic Application for Explain Relationships Between 222Rn Concentration and Earthquakes

Earthquake behaviors are, in general, among the non-linear topics of physics. Unfortunately researches up to now could not yet propose a complete mathematical model for earthquake behavior prediction possibilities. The main reason for not being able to establish such a model is due to the non-linear behavior of the earthquake and its generation is dependent on a variety of indigenous factors. Mathematical expressions and modeling of the non-linear systems is comparatively difficult and sometimes requires high speed and memory computers. For this reason, the expert systems as Fuzzy Logic (FL) are now commonly used for such modelling. Model is suggested a system to examine the space-time behavior of any physical phenomena through a set of convenient mathematical expressions, which describe linear or non-linear aspects. Fuzzy logic applications have a fast increase in past few years. Fuzzy logic modelling can be a very powerful explains about internal structure of dynamic system. The most commonly used indicator in earthquake prediction studies is soil radon gas (222Rn). In this study, we have tried to explain relationships between 222Rn and earthquakes using fuzzy logic. The application region is performed for 222Rn data of Mersin region near the East Anatolian Fault System, Turkey.

Geochemical characteristics of soil radon and carbon dioxide within the Dead Sea Fault and Karasu Fault in the Amik Basin (Hatay), Turkey

The study area is close to the boundary of three tectonic plates (Anatolian, Arabian, and African plates) and is characterized by important tectonic lineaments, which consist mainly of the Dead Sea Fault (DSF), the Karasu Fault, and the East Anatolian Fault (EAF) systems. To understand the origin of soil gas emanation and its relationships with the tectonics of the Amik Basin (Hatay), a detailed soil gas sampling was systematically performed. Together with CO2 flux measurements, >220 soil gas samples were analyzed for Rn and CO2 concentrations. The distribution of soil Rn (kBq/m3), CO2 concentration (ppm), and CO2 flux (g/m2/day) in the area appears as a point source (spot) and/or diffuses (halo) anomalies along the buried faults/fractures due to crustal leaks. The results revealed that Rn and CO2 concentrations in the soil gas show anomalous values at the specific positions in the Amik Basin. The trace of these anomalous values is coincident with the N-S trending DSF. CO2 is believed to act as a carrier for Rn gas. Based on the Rn and CO2 concentrations of soil gases, at least three gas components are required to explain the observed variations. In addition to the atmospheric component, two other gas sources can be recognized. One is the deep crust component, which exhibits high Rn and CO2 concentrations, and is considered the best indicator for the surface location of fault/fracture zones in the region. The other component is a shallower gas source with high Rn concentration and low CO2 concentration. Moreover, He isotopic compositions of representative samples vary from 0.94 to 0.99 Ra, illustrating that most samples have a soil air component and may have mixed with some crustal component, without significant input of the mantle component. Based on the repeated measurements at a few sites, soil gas concentrations at the same site were observed to be higher in 2014 than in 2013, which may be associated with the activity of the DSF in 2013–2014. This suggests that soil gas variations at fault zone are closely related to the local crustal stress, and hence are suitable for monitoring fault activities.

Slip rates and seismic potential on the East Anatolian Fault System using an improved GPS velocity field

The East Anatolian Fault System (EAFS) is the second major fault system in Turkey, following the North Anatolian Fault System (NAFS). Unlike the NAFS, which produced 11 large earthquakes in the last ∼75 years, the EAFS has been relatively quiet during the same period of time. While historical records show that the EAFS has the potential to produce large earthquakes, the fault slip rates on the EAFS were not studied in detail, and were not quantified sufficiently. This is possibly due to the relatively low seismicity and slow slip-rates of the EAFS with respect to the NAFS. However, the determination of the slip rates of the EAFS is equally important in order to understand the kinematics of the Anatolian plate.In this study, we collected and analyzed new survey-type GPS data, and homogeneously combined published velocities from other studies, to form the most complete GPS data set covering the EAFS. In particular, continuous GPS observations were utilized for the first time to study the northern part of the EAFS. The results of the analysis give well-constrained slip rates of the northwestern segments of the EAFS, which is further connected to the Dead Sea Fault System (DSFS) in the south.The results show that while the slip rate of the EAFS is nearly constant (∼10mm/yr) to the north of Türkoğlu, it then decreases to 4.5mm/yr in the south. The slip rate on the northern part of the Dead Sea Fault System (DSFS) was also found to be 4.2±1.3mm/yr, consistent with earlier studies. The contraction rates along the EAFS are below 5mm/yr, except for the northernmost part near Karliova, where it reaches a maximum value of 6.3±1.0mm/yr. The results also show that two well-known seismic gaps across the EAFS, Palu-Sincik and Çelikhan-Türkoğlu segments, have slip deficits of 1.5m and 5.2m and have the potential to produce earthquakes with magnitudes of Mw7.4 and Mw7.7, respectively.

Optically stimulated luminescence dating of Holocene alluvial fans, East Anatolian Fault System, Turkey

In this study, the optically stimulated luminescence dating technique was used to determine the time of deposition of alluvial sediment samples from the Türkoğlu-Antakya segment of the East Anatolian Fault System (EAFS) in Turkey. The double-single aliquot regenerative dose protocol on fine grain samples was used to estimate equivalent doses (De). Annual dose rate was computed using elemental concentration of uranium (U) and thorium (Th) determined by using thick-source alpha counting and potassium (K) concentrations using X-ray fluorescence and/or atomic absorption spectroscopy. The environmental dose was measured in situ using α-Al2O3:C chips inside plastic tubes for a year. The two different bulk sediment samples collected from the Islahiye trench yielded ages of 4.54 ± 0.28 and 2.91 ± 0.23 ka. We also obtained a 2.60 ± 0.18 ka age for the alluvial deposit in the Kıranyurdu trench and 2.31 ± 0.14 ka age for an excavation area called Malzeme Ocağı. These ages were consistent with the corresponding calibrated Carbon-14 (14C) ages of the region. The differences between the determined ages were insufficient to clearly distinguish the disturbance event from the effects of bioturbation, biological mixing, or other sources of De variation in the region. They provide a record of alluvial aggradation in the region and may determine undocumented historical earthquake events.

Sedimentology and stratigraphy of Cenozoic deposits in the Kağızman-Tuzluca Basin, northeastern Turkey

The Kagizman-Tuzluca Basin is located in the northeastern Anatolia, to the east of the intersection point (near Karliova) of the major North and East Anatolian Fault systems. This intermontane basin displays a thick sequence (over 2000 m) of mostly terrestrial deposits represented by repetitive alternations of the lake and fluvial environments ranging from ?Late Eocene/Oligocene to Middle/? Late Miocene. A marine incursion only mappable in the southeastern margin of the basin deposited limestones and sandy limestones rich in marine mollusks and nummulites, in particular N. fichteli that constrain an Early Oligocene age for this marine unit (Kagan Fm). The terrestrial basin-fill deposits show different thicknesses throughout the basin due to irregular bottom topography and tectonic configuration of the basin margins. The thickest deposits were accumulated along the different margins of the basin, which received high quantities of siliciclastics from meandering river, alluvial and coastal fans, fan delta/Gilbert-type delta and wave-worked fluvial delta. Climate changes have also driven the development of lake environments during distinct depositional periods. Siliciclastic-dominated overfilled lakes (Halikislak and Kizilkaya formations) and chemical-dominated underfilled lakes (Turabi and Tuzluca formations) were formed. They have been also classified as “Newark-type” and “Fundy-type” lakes, respectively. Fluvial systems evolved from high-energy meandering rivers deposited under humid climate (Gungoren Formation) to low-energy meandering rivers resulted from arid and semiarid climates (Cincavat Formation). The transitional intervals from ephemeral river-dry mudflat (Cincavat Formation) to saline pan/lake (Tuzluca Formation) indicate wadi-sand flat-playa fluvial systems. The chronostratigraphic constrains of the entire sequence remain poor and so far solely based on vertebrate fossil assemblages. The evaporitic Tuzluca Formation would be Middle Miocene in age due to its stratigraphic position over the Cincavat Formation.

Crustal structure of the North Anatolian and East Anatolian Fault Systems from magnetotelluric data

Magnetotelluric (MT) studies can map subsurface resistivity structure and have located zones of low resistivity (high conductivity) within major strike-slip fault zones worldwide which have been interpreted as regions of elevated fluid content. This study describes MT data from the eastern part of the North Anatolian and the East Anatolian Fault Systems (NAFS and EAFS) and presents the results of the first MT studies of these faults. The inversion of the MT data produced 2-D resistivity models which showed that both fault systems are underlain by a broad low resistivity zone that extended into the lower crust. However, the resistivity beneath the East Anatolian Fault System was much lower than beneath the eastern part of the North Anatolian Fault System. These conductors begin at a depth of 10km – not at the surface as on the central San Andreas Fault (SAFS). This difference is interpreted as being due to the fact that the EAFS and NAFS are young fault systems characterized in the upper crust by multiple fault traces – as opposed to the SAFS that has evolved into a single through going fault. Different stages of the seismic cycle may also influence the resistivity structure, although this is difficult to constrain without knowledge of time variations in resistivity structure at each location.

Evolution of neotectonic activity of East Anatolian Fault System (EAFS) in Bingöl pull-apart basin, based on fractal dimension and morphometric indices

This study is an attempt of a semi-automatic geomorphological GIS analysis based on morphometric indices. In the study, 10-m-resolution Digital Elevation Models (DEMs) are used to assess the neotectonic signals regarding the recent topographic developments and to attach additional significance to active tectonics in the Bingöl basin area. The methodology incorporates the determination of the structural similarities of the faults in the basins using fractal concepts and the application of four morphometric indices (Stream Power Index (SP), Multi-resolution Index of Valley Bottom Flatness (MRVBF), Terrain Ruggedness Index (TRI) and Valley Width-to-Height Ratio (Vf)). In order to detect the deviation from spatial randomness of the applied indices, the weighted correlation coefficient Moran’s I is used and the results are interpreted at a confidence interval of 99%. The spatial distribution of integrated index values is evaluated with the tectonically active fault zones in order to determine the probable activity and the structural deformation in the basin.The applied methodology reveals that the fractal analysis of the fault lines and the spatial analysis of the morphometric indices proved to be effective tools in analyzing the tectonic influence of the fault system on the basin area. Within the basin area, a relatively lesser degree of tectonic activity is observed, in contrast with the high tectonic activity outside the basin.

On the Correction of Spatial and Statistical Uncertainties in Systematic Measurements of 222Rn for Earthquake Prediction

In earthquake prediction studies, the regional behaviour of accurate 222Rn measurements at a set of sites plays a significant role. Here, measurements are obtained using active and passive radon detector systems in an earthquake-active region of Turkey. Two new methods are proposed to explain the spatial behaviours and the statistical uncertainties in the 222Rn emission measurements along fault lines in relation to earthquake occurrence. The absolute point cumulative semivariogram (APCSV) and perturbation method (PM) help to depict the spatial distribution patterns of 222Rn in addition to the joint effects of the K dr, the radon distribution coefficient, and the perturbation radon distribution coefficient (PRDC). The K dr coefficient assists in identifying the spatial distributional behaviour in 222Rn concentrations and their migration along the Earth’s surface layers. The PRDC considers not only the arithmetic averages but also the variances (or standard deviations) and the correlation coefficients, in addition to the size of the error among the 222Rn measurements. The applications of these methodologies are performed for 13,000 222Rn measurements that are deemed to be sufficient for the characterization of tectonics in the Keban Reservoir along the East Anatolian Fault System (EAFS) in Turkey. The results are evaluated for the Icme earthquake (M L 5.4, 5.7 km, 23 June 2011), which occurred in the vicinity of the EAFS.

Geochemical Monitoring Along the Türkoğlu (Kahramanmaraş)-Gölbaşı (Adıyaman) Segments of the East Anatolian Fault System

We revisited the historical and instrumental period records and recognized that due to Golbasi-Turkoglu and Turkoglu-Antakya segments of the East Anatolian Fault System (EAFS), densely populated Kahramanmaras district is at great seismic risk. Therefore, in this study, Golbasi-Turkoglu segment of East Anatolian Fault was continuously monitored by collecting data of different geochemical parameters of spring waters emanating from major fault segments (pH, temperature, conductivity, anion and cation concentrations) and correlating with seismicity. For this purpose, three online spring water observation stations located on the Golbasi-Turkoglu segment of EAFS which is the most important source of earthquakes for Kahramanmaras and its surroundings were established. Physical and chemical changes of the spring waters which are thought to be directly related to the fault were monitored. Spring water temperature and electrical conductivity and pH were measured on an hourly basis, whereas anion-cation concentrations were determined daily from bottled spring water samples. Dense seismology network run under the TURDEP Project (EOS Transactions, 88, 333–334, 2007) in the area provided means for monitoring earthquakes down to magnitude 1. We show that a magnitude 4.2 event (20 August 2008) caused significant changes in the geochemical parameters of a nearby spring. From the geochemical transients determined we conclude that there is a close relation between earthquakes and geochemical parameters of spring waters in the region. In order to see this correlation better, measurements of geochemical parameters should continue in the future.

Far-field tectonic effects of the Arabia–Eurasia collision and the inception of the North Anatolian Fault system

AbstractNew thermochronological data show that rapid Middle Miocene exhumation occurred synchronously along the Bitlis suture zone and in the southeastern Black Sea region, arguably as a far-field effect of the Arabia–Eurasia indentation. Collision-related strain focused preferentially along the rheological boundary between the multideformed continental lithosphere of northeastern Anatolia and the strong (quasi)oceanic lithosphere of the eastern Black Sea. Deformation in the southeastern Black Sea region ceased in late Middle Miocene time, when coherent westward motion of Anatolia and the corresponding activation of the North and East Anatolian Fault systems mechanically decoupled portions of the foreland from the Arabia–Eurasia collision zone.

Seismicity and strain accumulation around Karliova Triple Junction (Turkey)

GPS studies in Turkey date back to the early 1990s, but were mostly focused on the seismically active North Anatolian Fault System (NAFS), or on the more populated Western Anatolia. Relatively few studies were made of the seismically less-active East Anatolian Fault System (EAFS), although it has the potential to produce large earthquakes. In this study, we present the results of a combination of geodetic and seismological data around the Karliova Triple Junction (KTJ), which lies at the intersection of the North- and East Anatolian Fault Systems. In particular, the geodetic slip rates obtained through block modeling of GPS velocities were compared with b-values to assess seismicity in the region. Yedisu segment, one of the best-known seismic gaps in Turkey, was specifically analyzed. The relatively low b-values across Yedisu segment verify the accumulation of seismic energy in this segment, and the GPS-derived geodetic slip rates suggest that it has the potential to produce an earthquake of Mw 7.5 across an 80-km rupture zone.Additionally, analysis of earthquake data reveals that the study area has a ductile or rigid–ductile behavior with respect to its surroundings, characterized by varying b-values. Although, seismic events of moderate- to high magnitudes are confined along the major fault zones, there are also low-seismicity zones along the eastern part of the Bitlis Suture Zone and around Yedisu. Since the high seismicity areas within the region may not accumulate sufficient stress for a large earthquake to occur, it is considered that the deformation in such areas occurs in a ductile manner. On the other hand, the areas characterized by low b-values may have the capacity of stress accumulation, which could lead to brittle deformation.