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SUMMARY The offshore part of the North Anatolian Fault (NAF) beneath the Marmara Sea is a well-known seismic gap for future M > 7 earthquakes in the sense that more than 250 yr have passed since the last major earthquake in the Central Marmara region. Although many studies discussed the seismic potential for the future large earthquake in this region on the basis of historical record, geodetic and geological observations, it is difficult to evaluate the actual situation on the seismic activity and structure along the NAF beneath the Marmara Sea due to the lack of ocean bottom seismic observations. Using ocean bottom seismometer observations, an assessment of the location of possible asperities that could host an expected large earthquake is undertaken based on heterogeneities in the microseismicity distribution and seismic velocity structure. Specifically, seismic tomography and precise hypocentre estimations are conducted using offshore seismic data whose recording period is 11 months. About five times more microearthquakes are detected with respect to events recorded in a land-based catalogue. A comparison with previously published results from offshore observation data suggests that the seismicity pattern had not changed from 2014 September to 2017 May. The location accuracy of microearthquakes is greatly improved from only the land-based earthquake catalogue, particularly for depth direction. There are several aseismic and inactive zones of microearthquake, and the largest one is detected using land-based seismic observation, whereas other zones are newly detected via offshore observations. The obtained velocity model shows a strong lateral contrast, with two changing points. The western changing point corresponds to a segmentation boundary, where the dip angle of the NAF segments changed. High-velocity zones from tomographic images are characterized by low seismicity eastward of the segment boundary. To the east of 28.50°E, the high-velocity zone becomes thicker in the depth direction and is characterized by low seismicity. Although the low seismic activity alone could be interpreted as both strong coupling and fully creeping, the high-velocity features at the same can be concluded that these zones are consist of brittle material and strong coupling. From comparison with other geodetic and seismic studies, we interpret these zones as locked zones that had been ruptured by the past large earthquakes and could be ruptured by future ones. These zones might accumulate strain since the main shock rupture associated with the 1766 May Ms 7.3 earthquake, the latest major earthquake in this region.

As the earliest institute in Turkey dedicated to locating, recording, and archiving earthquakes in the region, the Kandilli Observatory and Earthquake Research Institute (KOERI) has a long history in seismic observation, which dates back to the installation of its first seismometers soon after the devastating Istanbul earthquake of 10 July 1894. For over a century, since the deployment of its first seismometer, the KOERI seismic network has grown steadily in time. In this article, we present the KOERI seismic network facilities as a data center for the seismological community, providing data and services through the European Integrated Data Archive (EIDA) and the Rapid Raw Strong-Motion (RRSM) database, both integrated in the Observatories and Research Facilities for European Seismology (ORFEUS). The objective of this article is to provide an overview of the KOERI seismic services within ORFEUS and to introduce some of the procedures that allow to check the health of the seismic network and the quality of the data recorded at KOERI seismic stations, which are shared through EIDA and RRSM.

In this study, seismic events in the Edirne district (Turkey) and its vicinity have been investigated in order to discriminate earthquakes from quarry blasts. A total of 150 seismic events with Md ≤ 3.5 duration magnitude from a seismic activity catalog between 2009 and 2014 recorded by the Enez (ENEZ), Erikli (ERIK) and Gelibolu (GELI) broadband stations operated by Bogazici University, Kandilli Observatory and Earthquake Research Institute Regional Earthquake-Tsunami Monitoring Center were used in this study. The maximum S-wave and maximum P-wave amplitude ratio of vertical component velocity seismograms, power ratio (Complexity) and total signal duration of the waveform were calculated. Earthquakes and quarry blasts were discriminated using the linear discriminate function (LDF) and back propagation feed forward neural networks, an artificial neural network (ANN) learning algorithm, taking the determination coefficient and variance account values between these parameters into consideration. Eighty-one (54%) of the total 150 seismic events studied were determined to be earthquakes, and sixty-nine (46%) of them were determined to be quarry blasts. The LDF and ANNs methods were applied to the data in Edirne and its vicinity using a pair of parameters and were compared to each other for the first time. The accuracy of the methods are 95% and 99% for LDF and ANNs, respectively.

Turkey is between three major tectonic plates, is the most active area of the Mediterranean region in terms of earthquake activity. Relative motions between the African, Arabian and Eurasian plates account for most of the tectonic activity in the region. As a result, the Anatolian plate has a high danger for seismicity. This consists of the North Anatolian Fault Zone (NAFZ), East Anatolian Fault Zone (EAFZ) and SE Anatolian Thrust Zone which form the borders of the Anatolian Plate and important active fault segments throughout Western Anatolia. All these active faults cause a short time intervals intensive damages in Turkey earthquakes. In order to investigate and to real-time monitor the seismic activity and seismotectonic of Turkey and its vicinity, The Kandilli Observatory and Earthquake Research Institute (KOERI) of Bogaziçi University and AFAD operates seismic stations countrywide. Observatory has been supplying mainly 3 kind of seismological data: phase readings, waveform and catalogue to the earth scientists in Turkey. Earth science studies have an important contribution to the emergence of earthquake hazard. The evaluation of the data receiving from the seismic stations contributes to the determination of earthquake hazard in detail, and to contribute to the minimization of the risks of the earthquake by developing earthquake catalogues. Also, all of the earthquake parameters after the earthquake, automatically distributed and mapped. After an important earthquake, KOERI and AFAD is quickly sent information from the smartphones to the society and the decision-making institutions carrying out disaster studies.

KOERI has a long history of earthquake seismology, beginning its observations right after the devastating earthquake on 10 July 1894 in Istanbul, by deploying the first seismograph in the region. Naturally, its seismic network and earthquake catalog evolved since that time, in harmony with the progress in the science of seismology. Currently, the seismic network consists of 242 stations that record approximately 1500 earthquakes per month during periods of regular seismicity. Magnitude is one of the most critical parameters in determining the size of an earthquake, especially in seismic hazard assessment studies. The objective of this study is to homogenize the magnitudes of the KOERI catalog between 2008 and 2018. For this aim, we computed the Magnitude of Completeness (Mc) for two different time periods between 2008–2011 and 2012–2018 by taking into account the duration magnitude (Md) and local magnitude (Ml), where these parameters might not be available jointly for the both time periods considered. As a result, we present a relationship of Md and Ml magnitudes derived from and applicable to KOERI's earthquake catalogs.

The offshore part of the North Anatolian Fault (NAF) beneath the Marmara Sea is a well-known seismic gap for future M > 7 earthquakes in the sense that more than 250 years have passed since the last major earthquake in the Central Marmara region. Here, an assessment on the location of possible asperities to host the expected next large earthquake is done based on the heterogeneities on the seismic velocity structure. Using long-term ocean bottom seismograph (OBS) observation data, seismic tomography and precise hypocenter estimations have been conducted. As a result, about five times more microearthquakes than the events in a land-based catalog has been detected. A comparison with previously published results suggests that the seismicity pattern has not changed during the three years period between Sep. 2014 and Jun. 2017. The obtained velocity model shows strong lateral contrast whose changing points locate at 28.10°E and 28.50°E. The western corner of the area (28.10°E) corresponds to a segmentation boundary where the dip angle of the NAF segments changed. The high velocity zones in the tomographic images are characterized by low seismicity eastward from the segment boundary at 28.10°E. Eastern 28.50°E, the high velocity zone becomes thicker in the depth direction. These zones are interpreted as asperities to be ruptured by the next large earthquake which are possibly accumulating strain since the mainshock rupture associated with the May 1766 Ms7.3 earthquake.

We investigate significant earthquake sequences in the observation period between 2000 and 2018 along the Tuz Golu Fault Zone in Central Anatolia. These sequences include a series of strong events with moment magnitudes (M-w) > 5.0, e.g. 30 July 2005 Bala-Ankara M-w 5.2, 20 December 2007 Bala-Ankara M-w 5J and 26 December 2007 M-w 5.6 Afar-Ankara earthquakes. The mainshocks are shallow focus strike-slip events with minor normal component at depths of 12-15 km. Focal depths of aftershocks range from 2 to 30 km. The focal mechanisms of the aftershocks are mainly normal faulting with variable strike-slip components. The geometry of focal mechanisms reveals a normal faulting regime with E-W and also NE-SW trending directions of T-axis in the entire activated region. A stress tensor inversion of focal mechanism data is performed to acquire a more accurate picture of the Tuz Gou Fault Zone stress field. The stress tensor inversion results display a predominant normal stress regime with a NNE SSW oriented maximum horizontal compressive stress (S-H). According to high-resolution hypocenter relocations of the Tuz Golu Fault Zone seismic sequences, eight clusters are revealed. The aftershock activities in the observation period between 5 March 2000 and 2 June 2018 extend from NW to SE direction. Seismic cross-sections show that a complex pattern of the hypocenter distribution with the activation of Tuz Gold Fault Zone segments. The western clusters are associated with a fault plane trending mainly N-S and dipping towards almost vertical, while the eastern clusters are related to a fault plane trending NW and dipping towards SE direction. The best constrained focal depths are mainly confined in the crust (depth < 30 km) and range from 2 to 30 km. In this study, we compare the results of an analysis of b-values from seismicity and stress tensors of focal mechanism solutions to understand their coupling in terms of faulting and earthquake hazard implications. In particular, this comparison allows to investigate the spatiotemporal correlation between b-values and stress distributions and it is therefore able to locate fault segments that have a high potential of generating large earthquakes. According to recent seismicity, b-values range from 0.5 to 1.5 along the Tuz Golu Fault Zone in Central Anatolia. The maximum horizontal compressive stress (S-H) indicates N-S and NE-SW directions while the minimum horizontal compressive stress (Sh) displays E-W. These results represent that low stress variances are correlated with high b-values. Low b-values are predominant in areas with high stress rates, consistent with a high heterogeneity of focal mechanisms.

Seismicity catalogs are the most important product of seismic network operating centers, especially for the earthquake hazard studies. Understanding the nature of regional catalogues has primary importance in shedding light on statistical parameters of the seismicity behavior of that given region. It is a well-known truth that man made inhomogeneties and artificial facts exist in the catalogs due to the change of infrastructure with time. Precisely determined earthquake parameters are important not only for understanding the seismicity and seismotectonics of a region but also for providing an accurate estimation of seismic hazard and risk parameters. In this study, we present an evaluation of Kandilli Observatory and Earthquake Research Institute (KOERI) - Regional Earthquake Tsunami Monitoring Center (RETMC) seismicity catalog for the time duration of 2013 – 2017. We mapped the magnitude of completeness, Mc, for Turkey for the RETMC catalog. We compared the results with the Mc values of different local earthquake sequences in the region, by also considering the variations of Mc with time. Results of the study will be a reference guide for researchers who benefit from RETMC-KOERI data.

Kandilli Observatory and Earthquake Research Institute (KOERI), Regional Earthquake-Tsunami Monitoring Center (RETMC) determine source parameters and share results to researchers for earthquakes with magnitude ≥4.5 in Turkey and surrounding region since 2005. In this study, source parameters for 146 earthquakes with a magnitude of M≥4.2 (2016-2019) were found by using the near-field and regional waveforms of KOERI-RETMC and Ministary of Interior Disaster and Emergency Management Presidency Prime Ministry Disaster and Emergency Management Presidency Earthquake Department (AFAD). It is thought that the moment tensor catalog created by KDRAE-BDTİM will be a reliable source for the researcher. In addition, the seismicity of 3 important earthquakes happened in Turkey of years 2016-2019 (Ayvacık-Çanakkale 2017, Gökova 2017 and Aegean Sea 2017) were also examined in this study., 2005 yılından beri Kandilli Rasathanesi ve Deprem Araştırma Ensititüsü (KRDAE), Bölgesel Deprem-Tsunami İzleme ve Değerlendirme Merkezi (BDTİM) Türkiye ve civarında meydana gelen büyüklüğü M≥4.5 olan depremler için kaynak parametrelerini belirlemekte ve çözümlerini araştırmacılar için paylaşmaktadır. Bu çalışmada da büyüklüğü M≥4.2 olan 146 deprem için (2016-2019) BDTİM ve Başbakanlık İçişleri Bakanlığı Afet ve Acil Durum Yönetimi Başkanlığı Deprem Dairesi (AFAD)’ne ait yakın-alan ve bölgesel dalga şekilleri kullanılarak kaynak parametreleri bulunmuştur. KDRAE-BDTİM tarafından oluşturulan moment tensör kataloğunun araştırmacılar için güvenilir bir kaynak olacağı düşünülmektedir. Ayrıca 2016-2019 yılları arasında meydana gelen ülkemiz için önem teşkil edecek 3 önemli depremin (Ayvacık-Çanakkale 2017, Gökova 2017 ve Ege Denizi 2017) depremselliği de çalışma kapsamında irdelenmiştir.

Gorgun, Ethem/0000-0002-4563-3296 WOS:000544243200004 Ayvacik district of canakkale province was hit by four moderate size earthquakes on 6 February 2017 03:51 M-w 5.2, 6 February 2017 10:58 M-w 5.1, 7 February 2017 02:24 M-W 5.2, 12 February 2017 13:48 M-w 5.3. Centroid moment tensor solutions for 60 events with moment magnitudes (M-w) between 3.4 and 5.3 are computed by applying a waveform inversion method on data from the Turkish and Greek broadband seismic networks. The time span of data covers the period between 1 January and 28 February 2017. The mainshock is a shallow focus normal event with strike-slip component at a depth of 10 km. Focal depths of aftershocks range from 3 to 24 km. The seismic moment (M-o) of the mainshock is estimated as 7.62 x 10(16) Nm. The calculated rupture duration of the Ayvacik mainshock is 3 s. The focal mechanisms of the aftershocks are mainly normal faulting with a minor strike-slip component. The geometry of focal mechanisms reveals a normal faulting regime with NE-SW trending direction of T-axis in the entire activated region. We perform stress tensor inversion to acquire more accurate picture for the regional stress field. The stress tensor inversion results indicate a predominant normal stress regime with a WNW-ESE oriented maximum horizontal compressive stress (S-H). With respect the newly determined focal mechanisms, the effect of the propagation of the North Anatolian Fault into Aegean Sea is very clearly pronounced. According to the double-difference relocation algorithm for the 2017 Ayvacik seismic sequence, ten clusters are revealed. In order to find these clusters, we use HypoDD software. According to the relative relocations from HypoDD, we define 10 clusters along the five profiles. The aftershock activity in the observation period between 1 January and 28 February 2017 extends from W to E direction. Seismic cross-sections indicate that a complex pattern of the hypocenter distribution with the ruptured segments. The western cluster is associated with a fault plane trending mainly N-S and dipping vertical, while the eastern is related to a fault plane trending NE-SW and dipping towards NW. The best constrained focal depths operate in the approximate depth range from 3 to 24 km. Coulomb stress analysis is performed to calculate the cumulative effect of all the earthquakes of the swarm and correlate it-with the activated region. Positive lobes with stress more than 3 bars are obtained, these values are large enough to trigger failure towards NW-SE of the swarm activity.

In this study, seismic events in Kula district (Manisa, Turkey) and its vicinity have been investigated and then natural and artificial seismic activities are discriminated. Total of 77 digital vertical component velocity seismograms of seismic activities with ML≤3.5 magnitude from seismic activity catalogs between 2009 to 2014 recorded by Manisa Kula (KULA) broadband station operated by Bogazici University, Kandilli Observatory and Earthquake Resarch Institute Regional Earthquake- Tsunami Monitoring Center (RETMC) were used in this study. The maximum S-wave and maximum P-wave amplitude ratio (Ratio) of vertical component velocity seismograms and power ratio for (1 and 12 sec.) (Complexity-C) and total signal duration (Duration) of the waveform were calculated. The earthquakes and the quarry blasts have been discriminated using linear discriminant function (LDF) and Back Propagation-Feed Forward Neural Networks (BPNNs) that is one of the learning algorithms at the artificial neural networks (ANNs) methods taking correlation between these parameters into consideration. 39 (51%) of the 77 seismic activities were identified as quarry blasts and 38 (49%) of them as earthquakes LDF and ANNs methods have been applied together for the first time for Ratio-C, Ratio-logS and Ratio-duration parameter pairs with the data of Manisa and surroundings, and earthquakes and quarry blasts have been distinguished from each other. LDF and ANNs methods were compared for each pair of parameters. Both of two methods are successful but the ANNs method has higher accuracy percentage values than LDF method when there is sufficient number of data. The accuracy percentages are different for a pair of Ratio versus C, for a pair of Ratio versus logS and for a pair of Ratio versus duration, respectively.

Western Anatolia is one of the most seismically active regions in Turkey. The high seismic activity is a result of a complex tectonic deformation dominated by the N-S extensional tectonic regime in Western Anatolia. This tectonic deformation is also a result of the relative movement of the African- Arabian plates towards the north, which causes the Anatolian plate to shift 2.5 cm per year towards W-SW. One of the largest fault zones in the Western Anatolia, Sultandağı Fault Zone (SFZ) has a northwest-southeast trend. SFZ, approximately 120 km long, is an important tectonic structure, which produced three major earthquakes (Mw> 6.0) between the years of 2000 -2002. Therefore, the most significant goals of this study were to monitor the micro-earthquakes along SFZ, to enrich the current seismic network and to increase the earthquake detection threshold in the region (Mc

A tsunami warning system providing services in the Eastern Mediterranean, Aegean, Marmara and Black Seas under the UNESCO Intergovernmental Oceanographic Commission (IOC)—Intergovernmental Coordination Group (ICG) for the Tsunami Early Warning and Mitigation System in the North-Eastern Atlantic, the Mediterranean and Connected Seas (NEAMTWS) framework was established in Turkey by the Kandilli Observatory and Earthquake Research Institute (KOERI) (Özel et al., 2011). KOERI’s Regional Earthquake and Tsunami Monitoring Center (RETMC) was established on the foundations of the legacy KOERI National Earthquake Monitoring Center (NEMC) by adding observation, analysis and operational capability related to tsunami early warnings after an extensive preparatory period during 2009 and 2011. The center initiated its test-mode 7/24 operational status as a national tsunami warning center in 2011, and after a one year period it became operational as a candidate tsunami warning center for NEAMTWS on 1 July 2012, together with CENALT (Centre d’Alerte aux Tsunamis—France) and followed by the NOA (National Observatory of Athens—Greece) on 28 August 2012, INGV (Instituto Nazionale di Geofisica e Vulcanologia—Italy) on 1 October 2014 and IPMA (Instituto Português do Mar e da Atmosfera—Portugal) on 1 February 2018, completing full coverage of the tsunami-prone regions monitored by NEAMTWS. In this paper, an overview of the progress and continuous improvement of KOERI’s tsunami early warning system will be presented, together with lessons learned from important tsunamigenic events, such as the 20 July 2017 Bodrum–Kos Mw 6.6 and 30 October 2020 Samos–Izmir Mw 6.9 earthquakes. Gaps preventing the completion of an effective tsunami warning cycle and areas for future improvement are also addressed.

We investigate significant earthquake sequences in the observation period between 2000 and 2015 along the Afyon-Aksehir Graben system in western Anatolia. These sequences include a series of strong events with moment magnitudes ( M w ) larger than 5.5, e.g. Eber ( M w 5.8), Sultandagi ( M w 6.5) and Cay ( M w 5.8) earthquakes. The mainshocks are shallow focus normal events at depths of 8–15 km. Focal depths of aftershocks range from 2 to 30 km. The focal mechanisms of the aftershocks are mainly normal faulting with variable strike-slip components. The geometry of focal mechanisms reveals a normal faulting regime with NNE-SSW trending direction of T -axis in the entire activated region. A stress tensor inversion of focal mechanism data is performed to acquire a more accurate picture of the Afyon-Aksehir Graben stress field. The stress tensor inversion results display a predominant normal stress regime with a NW–SE oriented maximum horizontal compressive stress ( S H ). According to high-resolution hypocenter relocations of the Afyon-Aksehir Graben seismic sequences, six clusters are revealed. The aftershock activities in the observation period between 17 January 2000 and 26 October 2015 extend from east to west direction. Seismic cross-sections show that a complex pattern of the hypocenter distribution with the activation of Sultandagi Fault segments. The western clusters are associated with a fault plane trending mainly E-W and dipping towards SE, while the eastern clusters are related to a fault plane trending NW-SE and dipping towards vertical. The best constrained focal depths are mainly confined in the crust (depth

Earthquakes trigger other earthquakes and build up clusters in space and time that in turn create a bias in seismic catalogues. Therefore, declustering is considered as a prerequisite in seismic studies, particularly for probabilistic seismic hazard analysis, not only to eliminate the bias but also to decouple mainshocks and triggered events. However, a declustering process is not a straightforward task due to the complex nature of earthquake phenomena. There exist several declustering methods that mostly employ subjective rules to distinguish between background seismicity and offsprings. Eventually, the final declustered catalogues usually deviate significantly according to the employed method. This issue is raising some concerns, such as how to select the most suitable declustering algorithm, or to assess how this selection affects seismic hazard assessment. In consequence, the main goal of this paper is to quantify the sensitivity of seismic hazard assessments to different declustering techniques. Accordingly, the recently compiled Turkish earthquake catalogue was declustered by making use of three declustering algorithms. A total of six declustered catalogues, two catalogues per method, one by implementing the default input parameters, and one by altering the free input parameters of the employed methods, were produced. The clusters of selected earthquakes were studied in terms of the spatial–temporal distribution of earthquake sequences. A sensitivity analysis was conducted through the major steps of seismic hazard assessment for Istanbul metropolitan city. The seismicity of Istanbul and surroundings was modeled on the basis of four areal source zones. Comparative studies showed that, while the selected declustering algorithm did not significantly affect the completeness periods of moderate to large size earthquakes, it considerably altered those of small magnitude events (e.g. Mw 4.3–5.2) and consequently the recurrence parameters of the source zones. Depending on the declustering algorithm and input parameters, the activity rate was observed to vary up to a factor of two. The differences in the declustered catalogues obtained from different declustering approaches resulted in considerable variations in seismic hazard estimations. The hazard maps at return periods of 475 and 2475 years indicated that peak ground acceleration values may vary up to 20% at some locations. Moreover, the differences in 5% damped elastic spectral accelerations at T = 0.2 for the return periods of 475 and 2475 years are about 18 and 12%, respectively, on the southern shores of Istanbul where the highest hazard levels are observed.

Both the geometry and the depth of the seismogenic zone of the North Anatolian Fault under the Marmara Sea (the Main Marmara Fault (MMF)) are poorly understood, in part because of the fault's undersea location. We recorded 10 months of microseismic data with a dense array of ocean bottom seismographs and then applied double-difference relocation and 3-D tomographic modeling to obtain precise hypocenters on the MMF beneath the central and western Marmara Sea. The hypocenters show distinct lateral changes along the MMF: (1) both the upper and lower crust beneath the Western High are seismically active and the maximum focal depth reaches 26 km; (2) seismic events are confined to the upper crust beneath the region extending from the eastern part of the Central Basin to the Kumburgaz Basin; and (3) the magnitude and direction of dip of the main fault change under the Central Basin, where there is also an abrupt change in the depth of the lower limit of the seismogenic zone. We attribute this change to a segment boundary of the MMF. Our data show that the upper limit of the seismogenic zone corresponds to sedimentary basement. We also identified several seismically inactive regions within the upper crust along the MMF; their spatial extent beneath the Kumburgaz Basin is greater than beneath the Western High. From the comparison with seafloor extensometer data, we consider that these regions might indicate zones of strong coupling that are accumulating stress for release during future large earthquakes.

The Earthquake Model of Middle East (EMME) project was carried out between 2010 and 2014 to provide a harmonized seismic hazard assessment without country border limitations. The result covers eleven countries: Afghanistan, Armenia, Azerbaijan, Cyprus, Georgia, Iran, Jordan, Lebanon, Pakistan, Syria and Turkey, which span one of the seismically most active regions on Earth in response to complex interactions between four major tectonic plates i.e. Africa, Arabia, India and Eurasia. Destructive earthquakes with great loss of life and property are frequent within this region, as exemplified by the recent events of Izmit (Turkey, 1999), Bam (Iran, 2003), Kashmir (Pakistan, 2005), Van (Turkey, 2011), and Hindu Kush (Afghanistan, 2015). We summarize multidisciplinary data (seismicity, geology, and tectonics) compiled and used to characterize the spatial and temporal distribution of earthquakes over the investigated region. We describe the development process of the model including the delineation of seismogenic sources and the description of methods and parameters of earthquake recurrence models, all representing the current state of knowledge and practice in seismic hazard assessment. The resulting seismogenic source model includes seismic sources defined by geological evidence and active tectonic findings correlated with measured seismicity patterns. A total of 234 area sources fully cross-border-harmonized are combined with 778 seismically active faults along with background-smoothed seismicity. Recorded seismicity (both historical and instrumental) provides the input to estimate rates of earthquakes for area sources and background seismicity while geologic slip-rates are used to characterize fault-specific earthquake recurrences. Ultimately, alternative models of intrinsic uncertainties of data, procedures and models are considered when used for calculation of the seismic hazard. At variance to previous models of the EMME region, we provide a homogeneous seismic source model representing a consistent basis for the next generation of seismic hazard models within the region.

Many catalogues, agency reports and research articles have been published on seismicity of Turkey and its surrounding since 1950s. Given existing magnitude heterogeneity, erroneous information on epicentral location, event date and time, this past published data however is far from fulfilling the required standards. Paucity of a standardized format in the available catalogues have reinforced the need for a refined and updated catalogue for earthquake related hazard and risk studies. During this study, ~37,000 earthquakes and related parametric data were evaluated by utilizing more than 41 published studies and, an integrated database was prepared in order to analyse all parameters acquired from the catalogues and references for each event. Within the scope of this study, the epicentral locations of M ≥ 5.0 events were firstly reappraised based on the updated Active Fault Map of Turkey. An improved catalogue of 12.674 events for the period 1900–2012 was as a result recompiled for the region between 32–45N° and 23–48E° by analyzing in detail accuracy of all seismological parameters available for each event. The events consist of M ≥ 4.0 are reported in several magnitude scales (e.g. moment magnitude, Mw; surface wave magnitude, MS; body-wave magnitude mb; local magnitude ML and duration magnitude Md) whereas the maximum focal depth reaches up to 225-km. In order to provide homogenous data, the improved catalogue is unified in terms of Mw. Fore-and aftershocks were also removed from the catalogue and completeness analyses were performed both separately for various tectonic sources and as a whole for the study region of interest. Thus, the prepared homogenous and declustered catalogue consisting of 6573 events provides the basis for a reliable input to the seismic hazard assessment studies for Turkey and its surrounding areas.

Reliable moment magnitude estimates for seismic events in the Middle East region can be difficult to obtain due to the uneven distribution of stations, the complex tectonic structure, and regions of high attenuation. In this study, we take advantage of the many new broadband seismic stations that have become available through improved national networks and numerous temporary deployments. We make coda envelope‐amplitude measurements for 2247 events recorded by 68 stations over 13 narrow frequency bands ranging between 0.03 and 8 Hz. The absolute scaling of these spectra was calculated based on independent waveform modeling solutions of the moment magnitudes for a subset of these events to avoid circularity. Using our 1D path calibrations, we determined coda‐based magnitudes for a majority of the events. We obtain fairly good agreement with waveform‐modeled seismic moments for the larger events ( M w >4.5) at low frequencies ( 0.7 Hz) because of unaccounted 2D path effects, as well as mixing of both Sn coda and Lg coda, which have different attenuation behavior. This scatter leads to increased variance in the magnitudes estimated for smaller events in which low‐frequency amplitudes are below the noise levels and the higher frequencies are the only signals available. We quantify the expected variance in coda envelope amplitudes as a function of frequency using interstation scatter as our metric. The net results of this study provide thousands of new 1D coda magnitude estimates for events in the broad region, as well as the necessary initial starting model for use in a new related 2D coda study (Pasyanos et al. , 2016). Online Material: Table of site terms and moment magnitudes.

Beneath the Marmara Sea, Turkey, the Main Marmara Fault (MMF), the offshore part of the North Anatolian Fault (NAF), is a well-known seismic gap for future M > 7 earthquakes. However, its detailed fault geometry and microearthquake activity have been debated for several decades. Using data acquired from long-term ocean bottom seismograph (OBS) observations, we made precise hypocenter estimations based on 3-D Vp and Vs velocity structures and assessed the fault geometry beneath the western and central parts of the MMF. The results indicate a segmentation boundary between the near-vertical western part and the south-dipping eastern part located around 28.10°E. Enriched OBS locations indicate microseismicity along both the inner and outer boundary faults of the Central Basin, especially on the western side. A comparison with previously published results suggests that the seismicity pattern has not changed for at least two years, between 2014 and 2016. Using a combined dataset of this and previous studies, lateral variations in the dip angle along the MMF fault segment from 27.4°E to 28.8°E were investigated. Based on this, we depicted on-fault seismicity along the MMF and defined three inactive areas of microseismicity. Two are located in the western segment, corresponding to the rupture area of the 1912 Ms. 7.4 earthquake, and the other, the largest, is located on the eastern segment. From a comparison of previous seismic and geodetic studies, it is considered that this area is a fully locked zone and has the potential for large earthquakes. Having compared the difference between hypocenter locations determined from OBSs and land-based stations, it is proposed that the epicentral locations of the mainshock and aftershocks of the September 26, 2019, M 5.7 earthquake are located much closer to the MMF than locations reported from only land-based results.

We examine the 16 April 2015 M w 6.0 offshore eastern Crete earthquake and its aftershock sequence in southern Aegean Sea. Centroid moment tensors for 45 earthquakes with moment magnitudes (M w) between 3.3 and 6.0 are determined by applying a waveform inversion method. The mainshock is shallow focus thrust event with a strike-slip component at a depth of 30 km. The seismic moment (M o) of the mainshock is estimated as 1.33 × 1018 Nm, and rupture duration of the mainshock is 3.5 s. The focal mechanisms of aftershocks are mainly thrust faulting with a strike-slip component. The geometry of the moment tensors (M w ≥ 3.3) reveals a thrust-faulting regime with NE–SW-trending direction of T axis in the entire activated region. According to high-resolution hypocenter relocation of the eastern Crete earthquake sequence, one main cluster consisting of 352 events is revealed. The aftershock activity in the observation period between 5 January 2015 and 7 July 2015 extends from N to S direction. Seismic cross sections indicate a complex pattern of the hypocenter distribution with the activation of three segments. The subduction interface is clearly revealed with high-resolution hypocenter relocation and moment tensor solution. The best constrained focal depths indicate that the aftershock sequence is mainly confined in the upper plate (depth

In the past few decades, the Black Sea has been the subject of intense geological and geophysical studies, including deep seismic sounding, reflection profiling, gravity and magnetic surveys for scientific and petroleum exploration purposes (Nikishin et al. 2010; Soson et al. 2010; Stephenson and Schellart 2010).

Turkey is located in one of the most seismically active regions in the world. Characterizing seismic source zones in this region requires evaluation and integration of geological, geophysical, seismological and geodetical data. This first seismotectonic database for Turkey presented herein was prepared, under the framework of the National Earthquake Strategy and Action Plan—2023. The geographic information system (GIS)-based database includes maps of active faults, catalogues of instrumental and historical earthquakes, moment tensor solutions and data on crustal thickness. On the basis of these data, 18 major seismotectonic zones were delineated for Turkey and the surrounding region. The compilation and storage of the seismotectonic data sets in a digital GIS will allow analyses and systematic updates as new data accrete over time. © 2016, Springer Science+Business Media Dordrecht. Mount Allison University Acknowledgments This work was carried out as the ‘Seismotectonic Maps of Turkey’ project supported by the General Directorate of Mineral Research and Exploration (MTA), Disaster and Emergency Management Authority (AFAD), Kandilli Observatory and Earthquake Research Institution (KRDAE) and General Command of Mapping (GCM). We gratefully acknowledge the MTA, AFAD, KRDAE and GCM for the support provided. Our thanks go to Jacob Chacko (FUGRO-SIAL) for editing the final versions of this manuscript. Additionally, the suggestions of two anonymous reviewers greatly improved this manuscript.

A review on the historical evolution of seismic hazard maps in Turkey is followed by summarizing the important aspects of the updated national probabilistic seismic hazard maps. Comparisons with the predecessor probabilistic seismic hazard maps as well as the implications on the national design codes conclude the paper. © 2018, Springer Science+Business Media B.V., part of Springer Nature. Acknowledgements T-SHM project is granted by AFAD and financially supported by TCIP. The members of this project (the co-authors of this paper) express their sincere gratitude to the administrations of these two entities, in particular the currently acting and former presidents of AFAD Dr. Mehmet Güllüog^lu, Mr. Halis Bilden and Dr. Fuad Oktay; the acting and former directors of AFAD Earthquake Department Dr. Murat Nurlu and Mr. Ulubey C¸eken; the AFAD project coordination team Mrs. Nazan Yılmaz Kılıc¸, Mrs. 'lknur Dalyan and Mr. Cenk Erkmen; the deputy director general of TCIP Mr. İsmet Güngör and the general secretary of TCIP Mrs. Serpil Öztürk. The valuable comments of the project reviewers are also greatly appreciated by the project team. This paper is reviewed by Professor Julian J. Bommer at Imperial College and Professor Abdullah Sandıkkaya at Hacettepe University. Their comments improved some of the discussions and illustrations in the paper. Finally, the first author appreciates the help of Prof. S¸es¸etyan in the preparation of Table 1 as well as Professor Özkan Kale and Mrs. Senem Tekin for the preparation/improvement of many figures in the paper.

A detailed study, based on ocean-bottom seismometers (OBSs) recordings from two recording periods (3.5 months in 2011 and 2 months in 2014) and on a high-resolution, 3D velocity model, is presented here, which provides an alternative view of the microseismicity along the submerged section of the North Anatolian fault (NAF) within the western Sea of Marmara (SoM). The nonlinear probabilistic software packages of NonLinLoc and NLDiffLoc were used for locating earthquakes. Only earthquakes that comply with the following location criteria (e.g., representing 20% of the total amount of events) were considered for analysis: (1) number of stations >= 5; (2) number of phases >= 6, including both P and S; (3) root mean square (rms) location error 8 km) along the axis of the Main Marmara fault (MMF). In contrast, the following features were observed: (1) a significant number of earthquakes occurred off-axis (e.g., 24%), with predominantly normal focal mechanisms, at depths between 2 and 6 km, along tectonically active, structural trends oriented east-west or southwest-northeast, and (2) a great number of earthquakes was also found to occur within the upper sediment layers (at depths < 2 km), particularly in the areas where free gas is suspected to exist, based on high-resolution 3D seismics (e.g., 28%). Part of this ultra-shallow seismicity appears to occur in response to deep earthquakes of intermediate (M-L similar to 4-5) magnitude. Resolving the depth of the shallow seismicity requires adequate experimental design ensuring source-receiver distances of the same order as hypocentral depths. To reach this objective, deep-seafloor observatories with a sufficient number of geophone sensors near the fault trace are needed.

The Aegean Sea, is one of the most seismically active areas of the Eastern Mediterranean region (Fig. 1). Generally, North Aegean Sea region has been tectonically developed after the collision of Arabian plate with the Eurasian in the Late Miocene time and the subsequent westward escape of the Anatolian Plate relative to the Eurasian Plate, during the Early Pliocene.

The Earthquake Model of Middle East (EMME) Project aimed to develop regional scale seismic hazard and risk models uniformly throughout a region extending from the Eastern Mediterranean in the west to the Himalayas in the east and from the Gulf of Oman in the south to the Greater Caucasus in the North; a region which has been continuously devastated by large earthquakes throughout the history. The 2014 Seismic Hazard Model of Middle East (EMME-SHM14) was developed with the contribution of several institutions from ten countries. The present paper summarizes the efforts towards building a homogeneous seismic hazard model of the region and highlights some of the main results of this model. An important aim of the project was to transparently communicate the data and methods used and to obtain reproducible results. By doing so, the use of the model and results will be accessible by a wide community, further support the mitigation of seismic risks in the region and facilitate future improvements to the seismic hazard model. To this end all data, results and methods used are made available through the web-portal of the European Facilities for Earthquake Hazard and Risk ( www.efehr.org ).

The Simav Earthquake that occurred on 19 May 2011 in western Turkey was investigated on the basis of seismological data and geological observations. Approximately WNW?ESE trending surface ruptures were observed on the Simav Fault. The focal mechanism parameters of the earthquake (Mw = 5.8) and its aftershocks (Mw??>??3.5) were estimated using time-domain moment tensor inversion. A total of 2245 events were located with Geiger?s conventional absolute location method then relocated using the double difference (DD) algorithm. The calculated locations at a depths between 2 and 16?km were found to be consistent with Coulomb stress variation in the area. Average variance reduction (VR) of the solutions was calculated as ~70%. The focal parameters of strike dip and slip of the main shock, occurring at a depth of 11?km dipping towards the NNE, were estimated at 277, 62 and ?92, respectively. The most striking indication of the study is that the area is dominated by normal faults with mainly WNW?ESE trends. It is also concluded that earthquakes in the region are caused by an active and regional NNE?SSW (N 12? E) trending (?3 axis) extension regime. The mean stress ratio is 0.80, indicating a triaxial stress state. This extension is probably associated with a slab?pull force and /or roll-back due to the complex subduction process of the African Plate beneath Anatolian block along both the Hellenic and Cyprus arcs in the eastern Mediterranean region.

The deformation of the North Aegean Sea is mainly controlled by the westernmost segments of North Anatolian Fault System. On 8 January 2013, a moderate earthquake (Mw=5.7) occurred in the North Aegean Sea. A series of aftershocks were occurred within four months following the mainshock, which have magnitudes varying from Ml=0.9 to 5.0. We have obtained a total of 23 earthquake moment tensor solutions that belong to the 2013 earthquake sequence. The source of this earthquake sequence is a N75 degrees E trending pure dextral strike-slip fault. The temporal and spatial distribution of the earthquakes indicate that the rupture unilaterally propagates from SW to NE. The stress tensor analysis shows that the direction of the regional compressive stress is WNW-ESE. The 1968 Aghios earthquake (Ms=7.3) and the 2013 North Aegean Sea earthquake sequences indicate that the regional stress has been transferred from SW to NE in this region. The 1672 Bozcaada earthquake (M=7.0) had been occurred to the north-east of the 2013 earthquake sequence. The elapsed time (342year) and the regional stress transfer point out that the 1672 earthquake segment is probably a seismic gap and it is a potential earthquake hazard for this region.

This article summarizes a recent study in the framework of the Global Earth model (GEM) and the Earthquake Model of the Middle East (EMME) project to establish the new catalog of seismicity for the Middle East, using all historical (pre-1900), early and modern instrumental events up to 2006. According to different seismicity, which depends on geophysical, geological, tectonic, and seismicity data, this region is subdivided to nine subregions, consisting of Alborz–Azerbaijan, Afghanistan–Pakistan, Saudi Arabia, Caucasus, Central Iran, Kopeh–Dagh, Makran, Zagros, and Turkey (Eastern Anatolia; after 30° E). After omitting the duplicate events, aftershocks, and foreshocks by using the Gruenthal method, and uniform all magnitude to Mw scale, 28,244 main events remain for the new catalog of Middle East from 1250 B.C. through 2006. The magnitude of completeness (Mc) was determined as 4.9 for five out of nine subregions, where the least values of Mc were found to be 4.2. The threshold of Mc is around 5.5, 5.0, 4.5, and 4.0, for the time after 1950, 1963, 1975, and 2000, respectively. The average of teleseismic depths in all regions is less than 15 km. Totally, majority of depth for Kopeh–Dagh and Central Iran, Zagros, and Alborz–Azerbaijan, approximately, is 15, 13, and 11 km and for Afghanistan–Pakistan, Caucasus, Makran, Turkey (after 30° E), and Saudi Arabia is about 9 km.

We provide a complete description of the characteristics of excitation and attenuation of the ground motion in the Lake Van region (eastern Turkey) using a data set that includes three‐component seismograms from the 23 October 2011 M w 7.1 Van earthquake, as well as its aftershocks. Regional attenuation and source scaling are parameterized to describe the observed ground motions as a function of distance, frequency, and magnitude. Peak ground velocities are measured in selected narrow frequency bands from 0.25 to 12.5 Hz; observed peaks are regressed to define a piecewise linear regional attenuation function, a set of excitation terms, and a set of site response terms. Results are modeled through random vibration theory (see Cartwright and Longuet‐Higgins, 1956). In the log–log space, the regional crustal attenuation is modeled with a bilinear geometrical spreading ![Graphic][1] characterized by a crossover distance at 40 km: ![Graphic][2] fits our results at short distances ( r is better at larger distances (40< r

On 23 October 2011 at 1341 local time, a strong earthquake (Mw = 7.1) occurred east of Lake Van (KOERI; Kandilli Observatory and Earthquake Research Institute). The focal parameters of the main shock and 29 aftershocks with M ≥ 4.0 were obtained from regional broadband seismic data from KOERI network by using Regional Moment Tensor Inversion Code (Dreger 2002). It is confirmed that the main shock had thrust faulting mechanism. The stress tensor analysis was completed using the focal mechanism solutions and the software developed by (Gephart Comp Geosci 16: 953-989, 1990). The maximum principal stress (P compressional) of the main shock is aligned in a N-S (NNW/SSE) direction and the tensional axis (T dilatation) is aligned in an E-W (ENE-WSW) direction. The b value is calculated as 0.96 using the maximum likelihood method (Utsu 1999).

Satellite remote sensing images play an important role in environmental monitoring for mining industry. There are a number of environmental variables, soil and surface variables, associated with mineral activities, that are to some extent detectable easily with satellite earth observation data. The aim of this paper is to detect the quarrying-mining activities are located in seismically active regions of Turkey using satellite images. Because mining-quarrying blasts have been observed and listed as earthquakes in the seismicity catalogue by seismic networks. The presence of mines-quarries in an active seismic zone can cause errors during the analysis of the distribution of microseismicity and the editing of seismic catalogs. Therefore, this study is a meaningful analysis for seismic networks interested in tectonic researches, because it highlights areas where need to pay careful attention is advisable for identification of mining-quarrying blasts. The new digital database was created using the satellite images of mining and quarrying areas taken from the Google Earth program ( http://maps.google.com ). In the study, approximately 721 known and illegal mining-quarrying sources have been detected. That were organized in an informational atlas includes information on locations, geographic coordinates and satellite images of the mining-quarrying sources in Turkey which can be distributed as a CD or on the WEB. Kekovali et al. (International Journal of the Physical Sciences 6(15), 3784–3794, 2011) estimated potential mining and quarry areas of Turkey from the Kandilli Observatory Earthquake Research Institute & National Earthquake Monitoring Center (KOERI-NEMC) seismic catalogs using daytime to nighttime ratio analysis (Qm). In this study, the correlation between the estimated satellite locations of the mining and quarrying activities and the areas with Qm ≥ 2.0 values taken from the previous study was examinated. The result of the study, the important potential mining-quarrying sources were estimated for Turkey includes: Kutahya, Mugla, Manisa, Balikesir, Istanbul, Izmit, Edirne, Bursa, Bilecik, Tekirdag, Ankara, Konya, Eskisehir, Malatya, Yozgat, Kirikkale, Malatya, Sanliurfa, Sinop, Trabzon. Monitoring and controlling mining-quarrying activities through traditional methods is quite difficult due to high costs and lengthy time in obtaining accurate and updated maps. The use of satellite images is an inexpensive and effective tool for mapping large mining-quarrying activity areas that can be also used to supplement data from environmental studies. In the future work, the satellite database can be processed and analyzed in order to produce a proper GIS database that includes important mining-quarrying sources of Turkey.

A unique and very interesting earthquake of magnitude Mw 7.2 occurred in the Van region of Turkey on October 23, 2011 that caused a heavy loss of human lives and properties. The earthquake occurred on a blind oblique thrust fault oriented towards the NE–SW direction and dipping towards NW as evidenced by focal mechanism solution and aftershock distribution. In this study, we analyzed the seismogenesis and earthquake triggering during this sequence with the help of estimated seismological parameters (b-value of frequency–magnitude relation, p-value of aftershocks temporal decay and D-value of fractal dimension), 2D mapping of b- and p-values, 3D mapping of b-value and coseismic Coulomb stress modeling. The estimated seismic b-value equal to 0.89 reveals that the mainshock occurred in a highly stressed region and sequence comprised larger magnitude aftershocks due to the presence of large size asperities within the rupture zone. The normal estimate of p-value (0.98) suggests a tectonic genesis of the aftershocks sequence. The estimated D-value equal to 1.80 reveals that rupture propagated in a two-dimensional plane filled up by fractures. The spatial 2D and 3D mapping of seismic b-value suggests that the Van earthquake originated in a highly heterogeneous fractured rock matrix with fluid intrusions into it at deeper depth beneath the mainshock hypocenter region. The estimated coseismic Coulomb stress using the variable slip model for depth range 0–30 km exhibits a ‘butterfly’ pattern and most of the aftershocks fall (90%) in the region of enhanced Coulomb stress. This suggests that most of the aftershock activities have been triggered by transfer of positive Coulomb stress due to coseismic slip of the mainshock. The results estimated in the present study have potential useful implications in future seismic hazard assessment and risk mitigation in Van and the surrounding regions.

Frequency distribution of azimuth and plunges of P- and T-axes of focal mechanisms is compared with the orientation of maximum compressive stress axis for investigating the frictional strength of three fault segments of North Anatolian fault (NAF) in eastern Marmara Sea, namely Princes’ Islands, Yalova–Cinarcik and Yalova–Hersek fault segments. In this frame, we retrieved 25 CMT solutions of events in Cinarcik basin and derived a local stress tensor incorporating 30 focal mechanisms determined by other researches. As for the Yalova–Cinarcik and Yalova–Hersek fault segments, we constructed the frequency distribution of P- and T-axes utilizing 111 and 68 events, respectively, to correlate the geometry of the principle stress axes and fault orientations. The analysis yields low frictional strength for the Princes’ Island fault segments and high frictional strength for Yalova–Cinarcik, Yalova–Hersek segments. The local stress tensor derived from the inversion of P- and T-axes of the fault plane solutions of Cinarcik basin events portrays nearly horizontal maximum compressive stress axis oriented N154E which is almost parallel to the peak of the frequency distribution of the azimuth of the P-axes. The fitting of the observed and calculated frequency distributions is attained for a low frictional coefficient which is about μ ≈ 0.1. Evidences on the weakness of NAF segments in eastern Marmara Sea region are revealed by other geophysical observations. Our results also show that the local stress field in Cinarcik basin is rotated ≈30° clockwise compared to the regional stress tensor in Marmara region derived from the large earthquakes, whereas the local stress tensor in Yalova–Cinarcik area is found to be rotated ≈30° counterclockwise. The rotation of the two local stress fields is derived in the area where NAF bifurcates into two branches overlaying large electrical conductor.

A detailed source and rupture process analyzes of the 10 June 2012 Oludeniz-Fethiye (Dodecanese Islands; Mw 6.1) earthquake has been carried out using inversion of both complex body waves and strong ground motion records. The rupture starting from the hypocenter propagated gradually to the southwest. The main rupture is modeled by a main asperity located 2–3 km beneath the hypocenter and two small asperities. The size of the effective source area is about 24 × 12 km, the rupture duration was approximately 12 s and the total seismic moment was estimated to be 1.955 × 1018 Nm. Continuation of compression from the Hellenic Arc to the southeast part of Fethiye Gulf in the north developed many active faults with complex geometries in the region. According to the stress field obtained from the focal mechanism solutions of the 10 June 2012 Fethiye (Dodecanese Islands; Mw 6.1) earthquake and M ≥ 3.5 earthquakes which occurred in Fethiye Gulf, the region between Fethiye Gulf and Rhodes Basin was deformed by the NW–SE oriented extension. (T-σ3) principal stress axis is dominant in the region. Additionally, NNW–SSE compression (P-σ1) in further southwest of Fethiye Gulf contributed to forming normal and strike-slip faults. Continuation of the NE–SW trending thrust faults located from the west limb of the Hellenic Arc to the southeast of Fethiye Gulf caused deformation in the region due to the seismotectonic model of the region. Both, normal faulting related to the “pure extension” occurred after the compression, and strike-slip faulting associated with the “transtension”, have been expressed by the spatial positions of the principal stress axes in the study area.

The 8–28 December 2013 Mw 5.0–5.8 Antalya Basin earthquake sequence in eastern Mediterranean is examined. Centroid moment tensors for 16 earthquakes with moment magnitudes (Mw) between 3.6 and 5.8 are determined by applying a waveform inversion method. All earthquakes are shallow focus thrust events at a depth of 40–45 km. The seismic moments (Mo) of the earthquakes are estimated as 4.10 × 1016–5.54 × 1017 N m and rupture durations of the mainshocks are 20–22 s. The focal mechanisms of the aftershocks are mainly thrust faulting with a strike-slip component and reveal NW–SE trending direction of T-axis in the entire activated region. According to high-resolution hypocenter relocation of the Antalya earthquake sequence, seven main clusters are revealed. The aftershock activity in the observation period between 1 December 2013 and 23 January 2015 extends in an N to S direction. A seismic cross-section indicates that a complex pattern of the hypocenter distribution with the activation of seven segments. The westernmost cluster (cluster 1) is associated with a fault plane trending mainly WNW–ESE and dipping vertical, while the cluster 5 is related to a fault plane trending NNE–SSW and dipping towards SSE. The best constrained focal depths indicate that the aftershock sequence is mainly confined in the crust (depth < 40 km) and are operating in the approximate depth range from 3 to 110 km. A stress tensor inversion of focal mechanism data is performed to obtain a more precise picture of the Antalya Basin stress field. The stress tensor inversion results indicate a predominant thrust stress regime with a NE–SW oriented maximum horizontal compressive stress (SH). According to variance of the stress tensor inversion, to first order, the Antalya Basin is characterized by a homogeneous interplate stress field. The Coulomb stress change associated with two mainshocks are also investigated to evaluate any significant enhancement of stresses along the Antalya Basin and surrounding regions. Positive lobes with stress of more than 0.4 bars are obtained for two mainshocks, indicating that these values are large enough to increase the Coulomb stress failure towards NE–SW and NW–SE directions, respectively.

The Isparta Angle (IA) is a reverse Λ-shaped morphotectonic structure located to the north of Antalya Gulf in the Eastern Mediterranean Sea. It resulted from the northward curvature of the originally E–W-trending Tauride orogenic belt owing to the nappe emplacements and related clockwise and anti-clockwise rotations in a time period of Early Paleocene to Early Pliocene. The IA is included in the southwest Anatolian tensional neotectonic domain and characterized by a series of grabens and horsts bounded by active normal faults of dissimilar length and trend. The evolutionary history of the graben-horst system is episodic. It is evidenced by two graben fills. These are older and modern (younger) graben fills separated by an intervening angular unconformity. The modern graben fill is nearly flat-lying (non-deformed) whereas older graben fill was deformed into a series of anticlines and synclines with ENE-trending curvi-linear axes by a short-term compressive tectonic regime operated in NNW–SSE direction duri...

In order to create high-resolution images of the crust and upper mantle in central Anatolia, we deployed a 2-year 71 station broadband embedded the Kandilli Observatory and Earthquake Research Institute (KOERI) of Bogazici University national seismic network. This study focuses on crust and upper mantle studies such as earthquake locations (especially micro-seismic activity) and shear wave splitting (SKS) analysis. Distribution of earthquake locations supports the presence of seismic activity partly localized along major tectonic structures. The CAFZ, generally considered to be less seismically active, shows a significant amount of seismic activity that is consistent with internal plate deformation. Additional seismicity is observed near volcanically active regions of central Anatolia. We found that velocities for the crust and uppermost mantle are; P waves 6.01 km/s, and 8.21 km/s, and for S waves 3.89 km/s, and 4.64 km/s, respectively. The shear-wave splitting analysis has been carried out on teleseismic data acquired by CD-CAT stations mainly from May-2013 to 2014. The averaged fast polarization directions in the EAFZ are fairly uniform and show NE-SW orientations, but they are well aligned with the EAFZ. Rapid spatial variations in splitting parameters are observed at the stations located in the Adana region.

The faults’ geometry and their seismic activity beneath the Marmara Sea have been under debate for a couple of decades. We used data recorded by three ocean bottom seismographs (OBSs) over a period of 3 months in 2014 to investigate the relationship of fault geometry to microseismicity under the western Marmara Sea in Turkey. We detected a seismic swarm at 13 to 20 km depth beneath the main Marmara fault (MMF), and the maximum depth of seismogenic zone was 25 km within the OBS observation area. These results provided evidence that the dip of the MMF is almost vertical and that the seismogenic zone in this region extends into the lower crust. Our analysis of past seismicity indicated that the seismic swarm we recorded is the most recent of an episodic series of seismic activity with an average recurrence interval of 2–3 years. The repetitive seismicity indicates that the MMF beneath the western Marmara Sea is coupled and that some of the accumulated strain is released every 2 to 3 years. Our study shows that OBS data can provide useful information about seismicity along the MMF, but more extensive studies using more OBSs deployed over a wider area are needed to fully understand the fault geometry and stick–slip behavior of faults under the Marmara Sea.

Different types of seismic activity were recorded in Konya, central Turkey, after the installation of broadband stations by the Kandilli Observatory and the Earthquake Research Institute (KOERI) in 2007. Fifty-nine seismic events with duration magnitudes (Md) between 2.2 and 3.5 were recorded by the Konya (KONT) station in 2007 for statistical analysis. In this study, the microseismic activity in the vicinity of Konya was classified by using the maximum peak amplitude ratio (S/P), power ratio, and spectral amplitude ratio of the vertical component of the seismograms; these differences were used as discriminants. The classification was carried out by using a linear discriminant function (LDF) between two different events. In the discrimination analysis between the quarry blast and the earthquakes, three variables were used together to increase the reliability instead of two variables. After adding one variable to the classification functions, the correct classification percentage increased to 98 from 95%. The results of this study indicate that about 10 and 90% of the selected events are earthquakes and quarry blasts, respectively.

We have investigated the spatial variation of the stress field along the fault rupture zone of the 1999 Izmit earthquake (Mw 7.4) using first-motion polarity data at seven distinct aftershock clusters. In our approach, the first-motion polarities of all the aftershocks in a cluster are simultaneously inverted to determine the stress tensor parameters and fault plane solutions of individual events, in accordance with the method of Horiuchi et al. (1995). Where post-seismic slip was significant (e.g., Sapanca, Sakarya-Akyazi, and Karadere segments), we obtained stress tensors with the fault parallel or fault normal maximum (σ1) and minimum (σ3) principal compressive stress axes, which may imply either low frictional coefficients or fault weakness. A stress tensor with similar features was derived from the Cinarcik cluster, where the aftershocks lie in a low-velocity zone beneath the geothermal area. The maximum principal stress axis tends to remain parallel to the trend of the pre-mainshock σ1 around the Yalova segment; this segment experienced little to no co-seismic displacements. The stress tensor around the Golcuk segment, where the largest surface displacement of 5.5 m was observed, was determined to be 20–25° counterclockwise rotated, but the aftershock alignment remained fault parallel. We interpret these results in terms of the strong crust. On the other hand, both the aftershock alignment and the stress tensor were found to be rotated in the Izmit earthquake epicentral region despite the lower co-seismic displacements. We attribute this feature to the weak crust.

We conducted a study of the spatial distributions of seismicity and earthquake hazard parameters for Turkey and the adjacent areas, applying the maximum likelihood method. The procedure allows for the use of either historical or instrumental data, or even a combination of the two. By using this method, we can estimate the earthquake hazard parameters, which include the maximum regional magnitude Mˆ max , the activity rate of seismic events and the well-known bˆ value, which is the slope of the frequency-magnitude Gutenberg-Richter relationship. These three parameters are determined simultaneously using an iterative scheme. The uncertainty in the determination of the magnitudes was also taken into consideration. The return periods ( RP ) of earthquakes with a magnitude M ≥ m are also evaluated. The whole examined area is divided into 24 seismic regions based on their seismotectonic regime. The homogeneity of the magnitudes is an essential factor in such studies. In order to achieve homogeneity of the magnitudes, formulas that convert any magnitude to an M S -surface scale are developed. New completeness cutoffs and their corresponding time intervals are also assessed for each of the 24 seismic regions. Each of the obtained parameters is distributed into its respective seismic region, allowing for an analysis of the localized seismicity parameters and a representation of their regional variation on a map. The earthquake hazard level is also calculated as a function of the form Θ = ( Mˆ max , RP 6.0 ), and a relative hazard scale (defined as the index K ) is defined for each seismic region. The investigated regions are then classified into five groups using these parameters. This classification is useful for theoretical and practical reasons and provides a picture of quantitative seismicity. An attempt is then made to relate these values to the local tectonics.

Structural, mass-wasting and sedimentation processes along an active dextral shear zone beneath the Gulf of Saros and the NE Aegean Sea were investigated on the basis of new high-resolution swath bathymetric data and multi-channel seismics. A long history of dextral shearing operating since the Pliocene culminated in the formation of a NE-SW-trending, ca. 800-m-deep basin (the so-called inner basin) in this region, which is bordered by a broad shelf along its northern and eastern sides and a narrow shelf at the southern side. The western extension of the North Anatolian Fault Zone (the Ganos Fault) cuts the eastern shelf along a narrow deformation zone, and ends sharply at the toe of the slope, where the strain is taken up by two NE-SW-oriented fault zones. These two fault zones cut the basin floor along its central axis and generate a new, Riedel-type pull-apart basin (the so-called inner depression). According to the bathymetric and seismic data, these basin boundary fault zones are very recent features. The northern boundary of the inner depression is a through-going fault comprising several NE-SW- and E-W-oriented, overlapping fault segments. The southern boundary fault zone, on the other hand, consists of spectacular en-echelon fault systems aligned in NE–SW and WNW–ESE directions. These en-echelon faults accommodate both dextral and vertical motions, thereby generating block rotations along their horizontal axis. As the basin margins retreat, the basin widens continuously by mass-wasting of the slopes of the inner basin. The mass-wasting, triggered by active tectonics, occurs by intense landsliding and channel erosion. The eroded material is transported into the deep basin, where it is deposited in a series of deep-sea fans and slumps. The high sedimentation rate is reflected in an over 1,500-m-thick basin fill which has accumulated in Pliocene–Quaternary times.