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The North Anatolian Fault Zone (NAFZ) is a prominent tectonic structure with a significant impact on the observed active deformation in Türkiye. Detailed knowledge of the seismic anisotropy in the crust and mantle along this nascent shear deformation zone provides insights into the kinematics associated with past and present tectonic events. We employed teleseismic earthquakes observed by the Dense Array North Anatolia seismic network to map 3‐ D variations in crustal and mantle anisotropy in/around the NW segment of the NAFZ. To achieve this, we first performed a harmonic decomposition analysis of P‐receiver functions. The results were then used as a priori information to conduct an anisotropic receiver function inversion with the Neighborhood Algorithm that enabled imaging of the actual orientation and geometry of anisotropic structures. SKS splitting measurements are further used to make a comparison between the anisotropic behavior of crustal and mantle structures. Crustal anisotropy parameters estimated in our analyses/models well identify the signature of deformation caused by accumulated strain in the earthquake cycle through the strike of shallow cutting faults in the brittle crust beneath the NAFZ. Diffuse intense anisotropic energy at lower crustal depths was attributed to lattice preferred orientation of crystals or partially molten lenses elongated along the shear direction. Strong harmonic energy variations beneath the northern part of the Istanbul Zone likely reflect imprints of LPO‐originated frozen fabric at shallow depths (0–20 km) associated with the palaeotectonic Odessa Shelf, Intra‐Pontide Suture Zones or remnants of the Tethys Ocean. Plain Language Summary: We analyze teleseismic observations of distant earthquakes to constrain past/present geodynamic events that have shaped the crust and upper mantle structure beneath the NAFZ and its vicinity. By means of established seismological methods, we discovered detailed patterns of crustal and mantle kinematics that give clues about how the Earth's layers deform. In particular, we found that faults in the region respond to earthquakes and are likely to be concentrated in the brittle part of the crust. The unique patterns beneath the north of the NAFZ indicates the signature of a different lithospheric domain, particularly associated with the Odessa Shelf in the lower crust and upper mantle. The crustal deformation caused by the NAFZ shows how strain builds up during earthquake cycles, leading to the creation of faults in the crust. The details of lateral and vertical variations of seismic anisotropy resolved in the study region helps us to better understand the geological processes that shape the Earth's structure in this particular area. Key Points: Vertically stratified seismic anisotropy exists in the crust and upper mantle along the north‐western part of the North Anatolian Fault Zone (NAFZ)The NAFZ does not appear to control the deformation beyond ∼20–25 km depthUnusually high anisotropy below the IZ reflects imprints of the frozen fabric associated with the paleo‐tectonic Odessa Shelf [ABSTRACT FROM AUTHOR]

The Sarıköy-İnova and the Çan-Bayramiç-Ezine fault zones (SIFZ, ÇBEFZ) comprise the southern strand of the North Anatolian Fault System in the Biga Peninsula. They are located in the area between Sarıköy to northeast and the Dalyan settlement around Bozcaada in the North Aegean Sea to southwest. Both of the fault zones are active. This is evidenced by the 6 March 1737 (Ms =7.0) İnova, 1st February 1809 Hurma (Ms = 6.1), and the 8 February 1826 Güllüce (Ms = 6.2) historical earthquakes resulted from these fault zones. Maximum lengths of fault segments comprising the SIFZ and the ÇBEFZ are 14 km and 15 km, respectively. Based on the maximum lengths of fault segments, the magnitude of the peak earthquakes to be originated from these faults are Mw = 6.3 and 6.6, respectively. Based on both the geological and geographic markers, the total right lateral offsets accumulated on the SIFZ and ÇBEFZ are 12 km and 20 km, respectively. These offset values imply to the slip rates of 4.6 mm/yr and 7.7 mm/yr, respectively. Five pull-apart basins were developed on both fault zones. These are the Sarıköy, İnova, Kazabat, Çan and Ezine-Bayramiç basins. The first three of them are pure strike-slip pull-apart basins, while the type of the rest basins is superimposed. The angular unconformity between the nondeformed basin fill of Quaternary age and the folded to thrust-faulted basement rocks of pre-Quaternary age reveals strongly that the pull-apart basins have formed during the Quaternary time. This relationship also reveals that the commencement age of the strike-slip neotectonic regime and formation of associated fault zones are the Early Quaternary. This work was dedicated to the retirement memory of Dr. Fuat Şaroğlu.

The historical and instrumental seismicity records along the continental transform faults in the Eastern Mediterranean region represent periodicities within centennial scales. Half a century ago, it was suggested that the spatiotemporal sequences of millennial-scale historical seismicity along the interplate structures represent seismicity switching between the North Anatolian Fault Zone and the East Anatolian Fault Zone. However, many individual historical seismicity catalogs published in the last decade indicate a comparable number of earthquakes in the North Anatolian and Dead Sea fault zones, but not in the East Anatolian Fault Zone. Seismicity records of the instrumental period indicate that the North Anatolian Fault Zone is currently at its peak level of activity. On the other hand, it is well known from the historical records that the seismically quiescent instrumental period of the Dead Sea Fault Zone is not representative of its potential. The comparison of various individual historical earthquake catalogs implies a successive activity for the North Anatolian and Dead Sea fault zones, with a discernible time delay. This observation lends supports to elastic coupling between these continental transform faults, resulting from the direct interaction between the movements of the Arabian and Anatolian plates. The evaluation of both historical and instrumental periods together reveals a possibility to speculate that the Dead Sea Fault Zone could enter a more active phase in the near future, potentially exhibiting a time lag in relation to the activity observed in the North Anatolian Fault Zone. [ABSTRACT FROM AUTHOR]

The Kocaeli region, located in the eastern Marmara near the North Anatolian Fault Zone, is well known as a zone of high seismic hazard due to its proximity to major fault zones and high seismic risk due to the dense distribution of critical industrial facilities in the area. The region experienced two major earthquakes in 1999 in Kocaeli (Mw = 7.4) and Duzce (Mw = 7.1). This study performs site-specific probabilistic and deterministic seismic hazard analyses at 14 sites in the Kocaeli basin. The multi-mode spatial autocorrelation, a modification to the original SPAC method, is performed to obtain the velocity profiles at the selected 14 sites. The updated method used here employs array-based measurement of seismic ambient noise and measures Rayleigh-wave velocity dispersion from which a one-dimensional shear-wave velocity profile is obtained using a series of small arrays of seismometers. In addition to the array data, the horizontal to vertical spectral ratios from the central stations of the array is used. After obtaining the velocity profiles at each site, site-specific seismic hazard analyses are performed. Probabilistic seismic hazard analysis results are compared to the design spectra from Turkey's current and previous seismic design codes. Analyses are also repeated with reference engineering bedrock conditions to investigate the contribution of site conditions to the seismic hazard. Numerical results of the study indicate the high seismic hazard in the region and highlight the significance of using local parameters in seismic hazard analyses. [ABSTRACT FROM AUTHOR]

This study aims to explain the relief characteristics of the Kızılırmak Basin south of the North Anatolian Fault Zone. For this purpose, the topographic position index, absolute height, hypsometric curve and integral, relative height, aspect, topographic openness, slope, slope length, slope form, terrain ruggedness, basin relief, relief ratio, and ruggedness number analyses were applied. It is also understood from morphometric parameters that the elements that determine the relief characteristics in the north of the study area are the high tectonic activity and lithological elements of the North Anatolian Fault. In the south, lithological and tectonically changing conditions and early established drainage systems toward the vicinity of Uğurludağ have led to the emergence of a more flattened and mature topography. The fact that the area around the Salur Strait in the south and the Hacıhamza Strait in the north, which separate these two different sections, shows some morphometric parameters related to ayoung topography indicates that the drainage relationship between the North Anatolian Fault Zone and the Central Anatolian Neogene lakes in the south was established in a very young geological past. Generally, the flow energy of the river basins is increased by the high values of terrain ruggedness index, basin relief, relief ratio, and ruggedness number. The highest of these parameters are found in the basins from Kös, İlgaz, Çal, and Saraycık mountains to the North Anatolian Fault Zone and Hacıhamza Fault Zone. All these suggest that tectonic influence on the relief properties of the work area is the most obvious factor. [ABSTRACT FROM AUTHOR]

Abstract The North Anatolian Fault Zone is a dextral system operating between the Eurasian and Anatolian plates in northern Turkey. Across the Marmara Sea south of İstanbul, it deforms at ~18 mm/year slip rate, where the statistics of historical earthquakes suggest that a few M7+ earthquakes are generated every ~250 years. Currently, M7+ earthquakes are overdue as this section of the fault has not been reactivated since the 1766 and 1754 earthquakes. In this frame, identifying the stress change by the 2019 M5.8 İstanbul–Silivri earthquake is essential to characterize its influence on the critically stressed Marmara Sea segments of the North Anatolian Fault Zone. To do this, we mapped not only the main segments but also the secondary faults in the vicinity of the 2019 M5.8 İstanbul–Silivri earthquake to locate the fault patch it reactivated, as well as to accurately model the fault segments, where it significantly changed the stress. The joint analysis of relocated hypocenters and the Coulomb stress modeling shows that the mainshock failed a SW–NE striking splay fault, generating a stress increase of up to three bars on the fault that has the potential to generate M7+ earthquake. Graphical Abstract

On June 14, 2020, Mw 5.9 Kaynarpınar earthquake occurred in the easternmost part of the North Anatolian Fault Zone, along the Yedisu Seismic Gap near the Karlıova Triple Junction. Following the event, various agencies reported different epicenter locations. This issue and the complex fault pattern around the triple junction caused uncertainties about the ruptured fault and the rupture mechanism. To define the geometry of the ruptured fault, we (1) held a field survey within a week of the mainshock, (2) correlated our field data with the multitrack InSAR data, (3) relocated the epicenter of the mainshock, and its aftershocks, and (4) implemented moment tensor inversion analyses to the earthquakes larger than M 3.3. We defined a ~ N70E-striking surface rupture and measured the average co-seismic dextral slip magnitude as ~ 16 ± 1 cm in the field which is compatible with the horizontal displacement magnitude measured by InSAR (13–15 cm). Since no ~ N70E-striking faults were reported in the existing active fault database, we examined the prominent geomorphological structures along the rupture area. We determined two dextral fault families along the eastern part of the Yedisu Seismic Gap; (1) NW–SE-striking faults of the North Anatolian Fault Zone, and (2) N70E-striking faults forming the Kaynarpınar–Yuvaklı Fault Zone. This fault zone, defined and named in this study, is a part of the N70E-striking faults of the Turkish–Iranian High Plateau and the North Anatolian Fault Zone. The fault zone must have carried some, if not most, of the dextral sense-of-slip in the easternmost part of the North Anatolian Fault Zone during the Quaternary. [ABSTRACT FROM AUTHOR]

The Ezinepazarı Fault (EPF) is an active segment that restricts the Niksar Basin in the central part of the North Anatolian Fault Zone and has been the source of the devastating Mw 8.0 earthquake in the last 100 years. Traces of the surface rupture of the EPF, which occurred in AD 1939, can still be observed in the field today as a right-lateral strike-slip character. While paleoseismological studies were mostly focused on the western part of the North Anatolian Fault Zone (NAFZ) in previous studies, the studies on the central and eastern parts of the NAFZ are rarely addressed. In this context, trench-based paleoseismology studies were carried out on the surface rupture traces in order to determine both historical/prehistoric earthquakes caused by the fault and the Quaternary period characteristics of the EPF. According to the data obtained, at least two historical earthquake activities have been detected besides the last 1939 earthquake on the EPF. Accordingly, the first and second events occurred in E1: 5871 ± 2300 BP and E2: 1651 ± 128 BP, respectively. When the determined data are compared with the historical earthquake catalogs, it is concluded that Event 2 (E2) can be correlated with the AD 343 Niksar earthquake; thus, the EPF has an irregular earthquake recurrence interval. [ABSTRACT FROM AUTHOR]

The North Anatolian Fault Zone is a dextral system operating between the Eurasian and Anatolian plates in northern Turkey. Across the Marmara Sea south of İstanbul, it deforms at ~18 mm/year slip rate, where the statistics of historical earthquakes suggest that a few M7+ earthquakes are generated every ~250 years. Currently, M7+ earthquakes are overdue as this section of the fault has not been reactivated since the 1766 and 1754 earthquakes. In this frame, identifying the stress change by the 2019 M5.8 İstanbul–Silivri earthquake is essential to characterize its influence on the critically stressed Marmara Sea segments of the North Anatolian Fault Zone. To do this, we mapped not only the main segments but also the secondary faults in the vicinity of the 2019 M5.8 İstanbul–Silivri earthquake to locate the fault patch it reactivated, as well as to accurately model the fault segments, where it significantly changed the stress. The joint analysis of relocated hypocenters and the Coulomb stress modeling shows that the mainshock failed a SW–NE striking splay fault, generating a stress increase of up to three bars on the fault that has the potential to generate M7+ earthquake. [ABSTRACT FROM AUTHOR]

Field observations and morphotectonic evaluations on the south of Ulubat Lake and the Susurluk valley show that the dominant active fault pattern consists of northeast-southwest and east northeast-west southwest right-lateral faults and northwestsoutheast normal faults developing between these strike-slip faults. We redefined the active faults in the south of Ulubat Lake and discovered that these northeast-southwest right-lateral faults control the route of Susurluk River. Based on these discoveries and evaluations, we can claim that the "bend model" previously proposed for the region is not valid, as seen in the Mustafakemalpaşa Fault and Balıkesir-Kepsut Fault examples. Instead, we suggest that the faults belonging to the southern branch of the North Anatolian Fault Zone extend to Akhisar and İzmir via Bursa, Susurluk, and Balıkesir. [ABSTRACT FROM AUTHOR]

In the present study, an approach is suggested for the settlement area where there is liquefaction and surface fault rupture hazard at the same time, which allows the assessment of land damage in case an earthquake occurred. Edremit (Balıkesir NW Turkey), mainly under the influence the Edremit Fault Zone in the southern branch of the North Anatolian Fault Zone, was chosen as the study area. According to paleo-seismological findings from the Narli trench, at least three similar earthquakes occurred on the same rupture of Edremit Fault Zone passing in the studied area. In addition, generally the groundwater level in the liquefiable alluvial soil varies between 0.5 and 6 m, and also the ratio of areas of liquefiable soil varies between 56 and 78% at different depths in the area. The buffer zone for the Edremit Fault Zone ruptures was defined based on the distance from the surface fault rupture in the study area, and it was seen that 15% of the study area is within the first-degree fault avoidance zone, while 43.5% is located within free zone. The safety factor against liquefaction for the soil layers was determined by using simple procedure based on SPT-N values, and then, the spatial distribution of the liquefaction potential index was obtained. It is found that 43% of the study area has high or very high liquefaction potential while the rate of the area where liquefaction is not expected is 27.8%. The liquefaction potential and the map showing the fault avoidance zones are important and successful in terms of individual hazard related to earthquake. However, the said maps do not allow to assess, simultaneously and completely, the realistic extent of the possible land damage in case an earthquake occurs. So, using the liquefaction potential index and the distance from the surface fault rupture, a new index, namely land damage index, was defined to create the microzonation of the seismic hazard for liquefaction and surface fault rupture-induced land damage. According to the zonation of land damage index, 29.7% of the study area is consists of Land Damage Zone I where settlement is not allowed. The main goal of the preparation of the said microzonation for the study area is to recognize the hazard from active faults, with respect to liquefaction and surface fault rupture, and to provide guidance to planners on how to mitigate the risk for different types of buildings. [ABSTRACT FROM AUTHOR]

We have investigated the time-dependent seismicity model of the earthquake occurrence on a regional basis through the North Anatolian Fault Zone (NAFZ). To that end, the studied region has been subdivided into 7 seismogenic zones considering the seismotectonic criteria, and then regional time and magnitude predictable (RTIMAP) model has been performed. Intervened times and magnitudes of main shocks produced in each zone have predictive properties defined by the RTIMAP. The probabilities of the next main shocks in 5 decades and the magnitudes of the next events have been estimated using the formation time and magnitude of the past events in the zones. In the second step of the study, we have considered 17 settlements located on the NAFZ to perform point-based site-specific seismic hazard analyses and to determine the design spectra and earthquake parameters using updated Turkish Earthquake Hazard Map. Eigen value and static adaptive pushover analyses have been applied for the sample reinforced concrete building using the design spectra obtained from each settlement. This sample building has been modelled with the same structural characteristics (i.e. material strength, column and beams, applied loads, etc.) for all of the settlements. We have determined that the earthquake building parameters differ from each other which indicates the significance of site-specific seismicity characteristics on the building performance. [ABSTRACT FROM AUTHOR]

The intersection of the Eurasian and Arabian plates and the smaller Anatolian Scholle created the Karlıova Triple Junction (KTJ) in eastern Turkey. In this study, we present analogue model experiments for this region and compare the results with our field observations and data from remote sensing imagery. Our comparison suggests that the sense of slip along curvilinear faults at the west of the KTJ changes along strike moving away from the principal displacement zones, from strike-slip to oblique normal and then to pure normal slip. Although, the active Prandtl cell model has been proposed to explain the overall regional fault pattern at eastern part of the Anatolian Scholle, the map view orientation of the secondary faults within the Karlıova wedge and performed analogue modelling results suggest that the passive wedge-shaped Prandtl cell model with a normal dip-slip component along slip lines is more appropriate in order to explain not only deformation pattern around the KTJ but also internal deformation of eastern part of the Anatolia. Moreover, these faults accumulate the significant amount of deformation that causes to the irregular earthquake behavior and the relatively lower geologic slip-rates along the main fault branch of boundary faults around the KTJ. Abbreviations: Strike-slip; Karlıova Triple Junction (KTJ); continental deformation; North Anatolian Fault Zone (NAFZ); East Anatolian Fault Zone (EAFZ);Varto Fault Zone (VFZ)

The base of the Quaternary was formally redefined in 2009 by the International Commision on Stratigraphy at 2.6 Ma by shifting a 800 ka, formerly part of the Pliocene epoch, into the Pleistocene. It has made tremendous impression in literature. The Quaternary period is unique because of its climatic characteristics; however, it is a geochronological unit, and a redefinition of its position would affect many areas, such as the definition of neotectonic period in Turkey. The major tectonic elements of the Eastern Mediterranean region are located in there. Recent studies related to neotectonics in Turkey present a consensus on the driving mechanism and age of this tectonic period: the late Pliocene (before the formal adding of Gelasian stage into the Quaternary period) westward escape of the Anatolian plate. Following the collision of the Arabian and Eurasian plates at ~11 Ma BP, the North Anatolian Fault Zone created in the east and the escape tectonics could not occur until the propagation of the North Anatolian Fault Zone to the Aegean Arc at ~2.5 Ma BP and gaining a transform fault character with a similar slip rate as in today. The spatial distribution of active faults in Turkey also supports such an approach. The great majority of them have no relations with the pre-Quaternary formations, on the other hand are bounding the Quaternary basins. In this study, the neotectonics of Turkey discussed within the view of the redefined Quaternary. The comparison suggests the using of the term Quaternary tectonics substantially coincides with neotectonics in literature for Turkey, because the base level of this period in this region overlaps with the redefined base level of the Quaternary period. [ABSTRACT FROM AUTHOR]

Turkey is bounded by the two of the most active fault zones: the North Anatolian Fault Zone (NAFZ) and the East Anatolian Fault Zone (EAFZ). Therefore, Turkey has experienced several great earthquakes (M > 7.0) in these fault zones. These earthquakes caused huge devastation on buildings and roads as a result of landslides and liquefaction. Because of these huge effects, we aim to evaluate earthquake hazards by calculating the conditional probability of an earthquake with three probabilistic models (Weibull, gamma, and lognormal) in three selected regions along the NAFZ and EAFZ. For this purpose, the model parameters were calculated by using maximum likelihood estimates from the earthquake (Mw ≥ 5.5) recurrence times that occurred between 1900 and 2016 in the study regions. The fitting of model and data were tested with the log-likelihood value, Akaike information criterion, and the Kolmogorov-Smirnov minimum distance criterion. The lognormal model is the best-fit model for three regions according to the Kolmogorov-Smirnov distance criterion while the gamma is the best for region 3 according to the other two test criteria. The gamma model gives the highest probability value (> 0.80) for all regions, and lognormal results reach the values > 0.90 for region 1 (t = 0, τ = 11), for region 2 (t = 0, τ = 7), and for region 3 (t = 0, τ = 11). These results indicated that the short-time-period earthquake probabilities are high in the study regions. On the other hand, this study will be very useful for assessing the seismic risk and constituting the disaster mitigation plans of the study regions. [ABSTRACT FROM AUTHOR]

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An M 7.4 earthquake occurred near the town of Izmit on August 17, 1999 causing enormous casualties and economic losses: over 15 000 victims and several thousand irreparably damaged buildings and structures. The earthquake produced a set of fractures and fissures in the ground extending for more than 70 km from the Gulf of Izmit, with a new tectonic fault being formed that is more than 150-km long. This paper reports results from mathematical modeling of the state of stress and strain in the epicentral zone before and after the Izmit earthquake along with seismological observations. The modeling used a method for calculating the state of stress and strain in a blocky elastic isotropic heterogeneous medium that has been disturbed by a system of faults caused by an external tectonic stress field, with the boundary conditions being specified from seismological data. We show that the epicenters of large crustal earthquakes tend to occur in areas of highly concentrated stress intensity under a definite relationship between the principal stresses. The aftershock process is due to the release of stresses produced by a new rupture, while the resulting aftershock clusters correlate spatially with the zone of released stress intensity. The tectonic rupture is assumed to propagate toward zones of high stress intensity. The results obtained in this study can be useful in a deterministic approach to the assessment and prediction of earthquake hazard, as well as the length and area of earthquake rupture. [ABSTRACT FROM AUTHOR]

North Anatolian Fault Zone, on which large earthquakes have occurred in the past, migrates regularly from east to west, and it is one of the most active faults in the world. The purpose of this study is to estimate the coda wave quality factor (Qc) for each of the five sub regionsthat were determined according to the fault rupture of these large earthquakes and along the fault. 978 records have been analyzed for 1.5, 3, 6, 9, 12 and 18 Hz frequencies by Single Backscattering Method. Along the fault, the variations in the Qc with lapse time are determined via, Qc = (136±25)f(0.96±0.027), Qc = (208±22)f(0.85±0.02)Qc = (307±28)f(0.72±0.025) at 20, 30, 40 sec lapse times, respectively. The estimated average frequency-dependence quality factor for all lapse time are; Qc(f) = (189±26)f(0.86±0.02) for Karliova-Tokat region; Qc(f) = (216±19)f(0.76±0.018) for Tokat-Çorum region; Qc(f) = (232±18)f(0.76±0.019) for Çorum-Adapazari region; Qc(f) = (280±28)f(0.79±0.021) for Adapazari-Yalova region; Qc(f) = (252±26)f(0.81±0.022) for Yalova-Gulf of Saros region. The coda wave quality factor at all the lapse times and frequencies is Qc(f) = (206±15)f(0.85±0.012) in the study area. The most change of Qc with lapse time is determined at Yalova-Saros region. The result may be related to heterogeneity degree of rapidly decreases towards the deep crust like compared to the other sub region. Moreover, the highest Qc is calculated between Adapazari – Yalova. It was interpreted as a result of seismic energy released by 1999 Kocaeli Earthquake. Besides, it couldn’t be established a causal relationship between the regional variation of Qc with frequency and lapse time associated to migration of the big earthquakes. These results have been interpreted as the attenuation mechanism is affected by both regional heterogeneity and consist of a single or multi strands of the fault structure.

The 1944 earthquake segment of the North Anatolian Fault Zone contains paleoseismological signatures of major earthquake events. The segment consists of three active main faults and secondary faults showing anastomosing fault pattern. Stratigraphic and structural relationships and radiocarbon ages from trench excavation reveal that the main active fault located at the northernmost part of the region has produced four major earthquakes events up to now. These events, from north to south, correspond to 1944, 1668, 967, and 300 AD earthquakes on the segment. Our findings suggest that earthquake recurrence interval on the segment range from 276 ± 30 to ~700 years. The amount of displacement caused by surface faulting and earthquake recurrence interval indicates that the slip rate along the 1944 earthquake segment is 17–21 mm/yr in the late Holocene. [ABSTRACT FROM AUTHOR]

The applicability of the time-dependent seismicity model was investigated for earthquakes occurrence along the North Anatolian Fault Zone. This region was separated into thirteen seismogenic zones by virtue of specific seismological and geomorphological criteria, and RTIMAP (regional time and magnitude predictable) model was applied for these zones. The data including in both instrumental period (Ms ≥ 5.5) until the beginning of 2016 and historical period (Io ≥ 9.0 corresponding to Ms ≥ 7.0) before 1900 have been used in the study. Interevent times and magnitudes of mainshocks generated in each zone have predictive properties expressed by the RTIMAP. For the region considered, the relationship with increasing slope between the time interval of the events and the magnitude of the preceding earthquake shows that this model is suitable. On the basis of these equations and taking into account the formation time and magnitude of the last events in each zone, probabilities to the next main shocks in five decades and the magnitudes of the next events were estimated. [ABSTRACT FROM AUTHOR]

Natural radioactivity is widespread in the earth and is present in different environment geological formations in the soil and rocks. Natural radionuclides in soil originate from the members of 238U and 232Th series, and 40K radionuclide is the main external source of radiation to the human body. In this study, concentrations of the natural radioactivity 226Ra, 232Th, and 40K are measured in soil samples collected along the Ganos fault. The radioactivity levels of the soil samples for the study are determined by scintillation gamma spectroscopy. Concentrations of 226Ra in the soil samples ranged from ND to 24.1 Bq kg−1, 232Th concentrations from ND to 40.2 Bq kg−1, and 40K concentrations from 315.9 to 748.9 Bq kg−1. Obtained results were compared with the literature data. [ABSTRACT FROM AUTHOR]

Analogue and numerical models show that strong or weak domains in a deforming ductile material cause stress concentrations that may promote strain localization. Such domains commonly occur in the lithosphere through variations in composition or mineral fabric. Here we use a 2D plane-stress, non-Newtonian, viscous model to explore how strain localization develops from an initial isolated weak inclusion. We use a temperature-dependent rheological law for which the material weakens as a result of work done by shear converted to heat. The progress of strain localization follows a power-law growth that is strongly non-linear and may be regarded as an instability. Although this localization mechanism is ultimately limited by thermal diffusion, this parametrization permits a robust criterion for the conditions in which localized shear zones can form within the lithosphere. Shear zones in the lower crust are typically depicted as the downward continuation of faults. We argue that the depth-extent of narrow shear zones within the lithosphere is limited by the stability criteria that we infer from 2D numerical experiments. When applied to the rheological laws for common lithospheric minerals, the combination of temperature and stress-dependence provides a direct means of predicting the depth below which the localization instability does not occur. For an olivine based rheology, the maximum depth at which rapid localization is expected is in the range of ~20 to 60 km, depending on heat flow, strain-rate and water fugacity. We apply our calculations to two major continental strike-slip zones, the San Andreas Fault and North Anatolian Fault, and compare our predicted maximum localization depths with published seismological images. Strain localization in the lower crust requires a dry rheology comparable to plagioclase. Observations that imply localized strain in the uppermost mantle beneath these fault zones are consistent with the localization criteria and the rheological properties of dry olivine. • Shear-heating enhances local strain concentration and promotes further localization. • Thermally activate localization in a shear zone follows a power-law type growth. • Strain localization rate depends on background temperature, depth and lithology. • Maximum localization depths are consistent with seismic images of major shear zones. • Thermal localization of mantle below continental Moho to ~60 km is possible. [ABSTRACT FROM AUTHOR]

This study investigates the 2D-lateral distribution of frequency-dependent crustal seismic attenuation parameters beneath the central part of the North Anatolian Fault Zone in Turkey. Parameter estimations are based on an optimal fit between observed and synthetically computed seismogram envelopes in four different frequency bands (1.5 to 12 Hz). The forward modeling of the synthetic data relies on acoustic radiative transfer theory under the assumption of multiple isotropic scattering. Lateral variations of intrinsic and scattering attenuation clearly separate the main branch of the central part of the fault zone. Comparisons between intrinsic and scattering attenuation imply that seismic energy loss in the region of the central part of the North Anatolian Fault Zone is clearly dominated by the process of intrinsic attenuation. As a by-product of the inversion, moment magnitudes of the investigated events are calculated. Comparison of coda-derived magnitudes with magnitudes obtained from the earthquake catalog indicate that the analytical inversion approach can successfully be applied, even in this tectonically complex regime. [ABSTRACT FROM AUTHOR]

U‐Th dating of carbonate veins in connection with active tectonics has recently been used as an attractive tool for constraining the absolute timing of late Quaternary crustal deformations. In this study, for the first time we correlate U‐Th ages of travertine deposits in coseismic fissures along the North Anatolian Fault Zone with records of paleoseismological studies supported by historical earthquake catalogued data. U‐Th ages are assessed in relation to the recurrence interval and the size and epicenter distance of major Holocene earthquakes. Our statistical evaluations on age correlations indicate that the carbonate vein precipitation is concentrated in eight different periods along the North Anatolian Fault Zone. The periods are well correlated with historical earthquake records and with previous dating results of the nearby trench studies. At least six of the periods correspond to the earthquakes reported in the historical catalogues. The age correlations of carbonate precipitation intervals for the last millennium show a recurrence along the eastern North Anatolian Fault Zone with a mode at 130–330 years that is consistent with a previously proposed paleoseismic recurrence interval of the fault. Recorded events in carbonate veins indicate a close‐epicenter (d < 200 km) and high‐intensity (I > VI) paleoearthquakes. Our results suggest that coseismic carbonate veins could be used to determine paleoseismic records as a supplementary tool to augment paleoseismological techniques. This tool has advantages over traditional paleoseismological methods for the understanding of long‐term earthquake behavior, particularly for prehistoric late Pleistocene events which cannot be dated easily by traditional paleoseismological methods. Key Points: Age distributions of coseismic carbonate veins are comparable with historical earthquakesCoseismic carbonates are precipitated with the close‐epicenter (d < 200 km) and high‐intensity (I > VI) earthquakesCoseismic carbonates are a good candidate to determine the long‐term seismic release records [ABSTRACT FROM AUTHOR]

Soil liquefaction is one of the ground deformations occurred during an earthquake which may cause serious damages such as settlement and tilting of structures due to loss of bearing capacity of foundations. Düzce and its surrounding settle on a plain which consists of silty and sandy layers with shallow groundwater level. Besides, the North Anatolian Fault Zone is a major seismic source which is capable of producing large magnitude earthquakes. All these data point out that the ground deformations like liquefaction and lateral spreading may occur during a probable large earthquake around Düzce and its close vicinity. In this study, the geotechnical data of 40 boreholes drilled to determine the local ground conditions and the groundwater level in Düzce were considered. Based on the field studies, it was aimed to evaluate the liquefaction potential considering the fact that the groundwater level is shallow as well as the subsurface soil is composed of loose alluvium. Liquefaction Potential Index (LPI) and Liquefaction Severity Index (LSI) methods were taken into account and the liquefaction potential of Düzce province was determined and mapped with respect to various earthquake scenarios in GIS environment. These maps are compared on the basis of different scenarios. Accordingly, it is concluded that the liquefaction potential is high-very high in the south and south-eastern sections of the study area where the construction of new residential buildings progressively continues. [ABSTRACT FROM AUTHOR]

The intersection of the Eurasian and Arabian plates and the smaller Anatolian Scholle created the Karlıova Triple Junction (KTJ) in eastern Turkey. In this study, we present analogue model experiments for this region and compare the results with our field observations and data from remote sensing imagery. Our comparison suggests that the sense of slip along curvilinear faults at the west of the KTJ changes along strike moving away from the principal displacement zones, from strike-slip to oblique normal and then to pure normal slip. Although, the active Prandtl cell model has been proposed to explain the overall regional fault pattern at eastern part of the Anatolian Scholle, the map view orientation of the secondary faults within the Karlıova wedge and performed analogue modelling results suggest that the passive wedge-shaped Prandtl cell model with a normal dip-slip component along slip lines is more appropriate in order to explain not only deformation pattern around the KTJ but also internal deformation of eastern part of the Anatolia. Moreover, these faults accumulate the significant amount of deformation that causes to the irregular earthquake behavior and the relatively lower geologic slip-rates along the main fault branch of boundary faults around the KTJ. Abbreviations: Strike-slip; Karlıova Triple Junction (KTJ); continental deformation; North Anatolian Fault Zone (NAFZ); East Anatolian Fault Zone (EAFZ);Varto Fault Zone (VFZ) [ABSTRACT FROM AUTHOR]

Abstract We analysed the interplay between coastal uplift, sea level change in the Black Sea, and incision of the Kızılırmak River in northern Turkey. These processes have created multiple co-genetic fluvial and marine terrace sequences that serve as excellent strain markers to assess the ongoing evolution of the Pontide orogenic wedge and the growth of the northern margin of the Central Anatolian Plateau. We used high-resolution topographic data, OSL ages, and published information on past sea levels to analyse the spatiotemporal evolution of these terraces; we derived a regional uplift model for the northward-advancing orogenic wedge that supports the notion of laterally variable uplift rates along the flanks of the Pontides. The best-fit uplift model defines a constant long-term uplift rate of 0.28 ± 0.07 m/ka for the last 545 ka. This model explains the evolution of the terrace sequence in light of active tectonic processes and superposed cycles of climate-controlled sea-level change. Our new data reveal regional uplift characteristics that are comparable to the inner sectors of the Central Pontides; accordingly, the rate of uplift diminishes with increasing distance from the main strand of the restraining bend of the North Anatolian Fault Zone (NAFZ). This spatial relationship between the regional impact of the restraining bend of the NAFZ and uplift of the Pontide wedge thus suggests a strong link between the activity of the NAFZ, deformation and uplift in the Pontide orogenic wedge, and the sustained lateral growth of the Central Anatolian Plateau flank. Highlights • Multiple fluvial, deltaic and coastal terraces along the Black Sea coast of Turkey. • New terrace chronology that spans the last 545 ka (MIS 14). • The uplift of the Central Pontides sustained at a rate of 0.28 ± 0.07 m/ka. • A northward-growing orogenic wedge that spatially coincides with a restraining bend. • The lateral growth of the northern flanks of the Central Anatolian Plateau. [ABSTRACT FROM AUTHOR]

The North Anatolian Fault (NAF) is one of the most well-known continental strike slip faults, however, the details related to the geodynamic processes and the extent of deformation in the crust remain poorly understood. Within the context of the Dense Array for North Anatolia (DANA) project, a comprehensive data set was gathered from a dense temporary seismic network consisting of 70 stations that were deployed in early May 2012 and operated for 18 months in the Sakarya region and the surroundings. With the aim of further exploring the crustal deformation near the fault mainly caused by the strike slip motion also resulting in the alignment of minerals, the crustal seismic anisotropy beneath the western segment of NAF was investigated by local shear wave splitting analysis. Out of 1371 events, 90 well located earthquakes were extracted with magnitudes >1.4 corresponding to a total of 645 splitting measurements. This method makes use of earthquakes nearby or directly below each station benefiting from the fast polarization direction and the relevant delay time parameters as the main output. Despite the scattered patterns, the fast orientations are dominantly E -W parallel to the fault strike. Delay times between the fast and slow components of the shear wave vary between 0.01 and 0.3 s clearly revealing the existence of crustal anisotropy. In particular, measurements at each station exhibits spatial variations across the fault where it splays into two main branches beneath the study area separating different geologic units. A strong correlation could not be established between small scale faults and azimuthal anisotropy. The measurements presented here constrain crustal anisotropy above the deepest earthquakes at approximately 15 km depth. • The extent of crustal anisotropy beneath the western segment of North Anatolian Fault. • Fast direction and delay time measurements revealed and scattering highlighting this structural complexity of active tectonic units. • Based on the observations, it might be suggested that there is not a strong coupling between mantle and crustal anisotropy. [ABSTRACT FROM AUTHOR]

Urban transformation in Turkey occurs in a rapid and disorganized form that causes major problems during disasters. In countries such as Turkey, where natural disasters occur frequently, sensitivity to urban planning and natural disasters should be addressed using geophysical, geotechnical and microzonation maps. This paper aims to show the results of seismic microzonation maps that define soil problems and interpret results with appropriate approaches that use multiple parameters, including shear wave velocity soil amplification, soil fundamental frequency and electric resistivity, from a series of geophysical measurements made on a 540-ha area in the city of Bursa, NW Turkey. In urban transformation studies, non-destructive techniques generated by geophysical applications have been considered to be a first step when monitoring the ground surface in archaeological buildings and old residential areas, such as in Bursa, which was once the capital city of the Ottoman Empire. In this study, a flowchart in five basic steps, developed for the organization of a successful urban transformation study, based on microzonation. These steps include 1- general properties of the study area (regional tectonic and seismotectonic), 2- characteristics of earthquakes and soils, 3- site characterization and type of soil problems, 4- data availability and quality, and 5- evaluation of results and decision-making. The results are re-organized to achieve systematic criteria for urban transformation. Remarkably, no standard criteria currently exist. This study illustrates that geophysical data provide a useful basis for land-use planning in cities at risk of earthquakes. [ABSTRACT FROM AUTHOR]

Abstract: We analyze waveforms of local earthquakes occurring before, between, and after the two consecutive 1999 Mw > 7 İzmit and Düzce earthquakes in NW Turkey. The waveforms were recorded at three seismic stations DOK, EKI, and GOK located around the Mudurnu segment of the North Anatolian Fault Zone. We focus on the interpretation of a distinct secondary phase contained in the P wave coda that is well separated from the direct P wave. The phase is visible in many waveforms of most seismicity clusters and has a specific constant time delay after the direct P wave arrivals at each station, irrespective of epicentral distance, hypocentral depth, or back azimuth. Based on a polarization analysis of records at station GOK, this secondary phase is interpreted as a PS wave converted at an interface near the stations. Its particle motion is consistent with the direct S wave and displays S wave splitting produced by the anisotropic upper crust. Synthetic modeling indicates that this PS phase can be converted either at a horizontal interface or at a steeply inclined interface. The steep Mudurnu fault zone with the near‐surface setting indicating a juvenile pull‐apart structure fits well into these interpretations, which are in agreement with the eastward progressing transtensional tectonics known for the region. [ABSTRACT FROM AUTHOR]

The Kuzulu (Koyulhisar) landslide occurred near the North Anatolian Fault Zone (NAFZ) on 17 March 2005 resulted loss of life and property. NAFZ is an active fault and is thought to trigger landslides in the region. In order to investigate this effect and minimize landslide damage; prediction of landslide or landslides susceptible areas need to be identified by likelihood methods. Firstly a inventory map for landslide were produced using inventory map of General Directory of Mineral Research, field surveys and aerial photographs. These landslides are randomly divided into two groups that 65% were used in analysis and 35% used for verification. Lithology, aspect, slope gradient, topographical elevation, distance to stream, roads and faults were decided to used in analysis as contributing factors after field studies. Landslide susceptibility map (LSM) of the Suşehri province of Sivas near the NAFZ was created by the Frequency Ratio method. LSM was separated into five classes from very low to very high. For validation of the map and evaluate its success, it was compared with the landslide which was not used in modeling. Consequently the area under curve (AUC) value was determined as 0.622. AUC value showed that the LSM was useable. With LSM, it is possible to avoid the loss of life and property by the engineering measures to be applied considering the possibility of landslide in the plans to be made in the areas where the possibility of landslide event in the region is high. [ABSTRACT FROM AUTHOR]

• The Bursa Basin formed as a transtensionally rotated pull-apart basin along the NAFZ. • Crosscutting relationship of faults defines the superposition of stress regimes. • Paleostress reconstructions determine two different deformation states since the Miocene. • The Quaternary basins originated from strain partitioning. • A 7.3 magnitude earthquake is possible to occur around Bursa. The present tectonic framework of NW Turkey has been dominated by two major deformational settings. The first of these is the West Anatolian Extension, which is associated with the collision along the Aegean-Cyprian subduction system between the Eurasian and African plates since the Oligocene. Second is the transcurrent tectonic setting, which developed with the westward movement of the Anatolian Block and compensates the displacement differencial motion the Anatolian Block and the Eurasian Plate. This led to the formation of one of the most well-known transform faults, the North Anatolian Fault Zone, which produced many devastating earthquakes. Bursa Basin has a unique position for understanding the stress partitioning that developed in the interaction area between these two extensional and transcurrent tectonic systems. In this study, the fault architecture throughout the basin has been identified and mapped in detail. Paleostress analysis based on 834 kinematic data from 20 sites indicates that the region has experienced two different deformation phases since the Miocene. The first phase is characterized by pre-Quaternary strike-slip deformation that formed under the NW–SE directed extension and NE–SW trending contraction. The second, ongoing deformation phase is characterized by NE–SW trending extension highlighting the stress conditions of the Bursa Basin. This phase marks the domination of NAFZ over the West Anatolian Extensional Province and the formation of the transtensionally rotated pull-apart basins between the branches of the North Anatolian Fault Zone, such as Bursa Basin. [ABSTRACT FROM AUTHOR]

The increase in the wealth of information on the seismotectonic structure of the Marmara region after two devastating earthquakes (M7.6 Izmit and M7.2 Duzce events) in the year 1999 opened the way for the reassessment of the probabilistic seismic hazard in the light of new datasets. In this connection, the most recent findings and outputs of different national and international projects concerning seismicity and fault characterization in terms of geometric and kinematic properties are exploited in the present study to build an updated seismic hazard model. A revised fault segmentation model, alternative earthquake rupture models under a Poisson and renewal assumptions, as well as recently derived global and regional ground motion prediction equations (GMPEs) are put together in the present model to assess the seismic hazard in the region. Probabilistic seismic hazard assessment (PSHA) is conducted based on characteristic earthquake modelling for the fault segments capable of producing large earthquakes and smoothed seismicity modelling for the background smaller magnitude earthquake activity. The time-independent and time-dependent seismic hazard results in terms of spatial distributions of three ground-shaking intensity measures (peak ground acceleration, PGA, and 0.2 s and 1.0 s spectral accelerations (SA) on rock having 10% and 2% probabilities of exceedance in 50 years) as well as the corresponding hazard curves for selected cities are shown and compared with previous studies.

The Havran-Balıkesir Fault Zone (HBFZ) is one of the major active structures of the Southern Marmara Region, which has been shaped by the southern branch of North Anatolian fault since the Pliocene. HBFZ is a 10–12 km wide, 120 km long, right-lateral strike-slip fault zone that consists of two ENE-striking main faults, namely, the Havran-Balya and Balıkesir faults. The 90-km-long Havran-Balya fault exhibits right-stepping en echelon geometry and is made up of (1) Havran, (2) Osmanlar, (3) Turplu and (4) Ovacık fault segments. On the eastern part, the 70-km-long Balıkesir fault is divided into two fault segments; (1) Gökçeyazı and (2) Kepsut. We estimated the long-term slip rate between 3.59 and 3.78 mm/yr using river offset. The Kepsut, Gökçeyazı and Ovacık fault segments are capable of generating an earthquake with a moment magnitude of up to 7.2. Detailed palaeoseismological studies show that the HBFZ is responsible for some surface faulting earthquakes with an average recurrence interval of 1000–2000 years during the late Holocene. Considering the fact that there was no evidence of a surface-ruptured earthquake for 2000 years, it can be stated that there is a seismic gap on the Gökçeyazı fault segment. [ABSTRACT FROM PUBLISHER]

Constraining the maximum likely magnitude of future earthquakes on continental transform faults has fundamental consequences for the expected seismic hazard. Since the recurrence time for those earthquakes is typically longer than a century, such estimates rely primarily on well-documented historical earthquake catalogs, when available. Here we discuss the maximum observed earthquake magnitudes along different sections of the North Anatolian Fault Zone (NAFZ) in relation to the age of the fault activity, cumulative offset, slip rate and maximum length of coherent fault segments. The findings are based on a newly compiled catalog of historical earthquakes in the region, using the extensive literary sources that exist owing to the long civilization record. We find that the largest M7.8–8.0 earthquakes are exclusively observed along the older eastern part of the NAFZ that also has longer coherent fault segments. In contrast, the maximum observed events on the younger western part where the fault branches into two or more strands are smaller. No first-order relations between maximum magnitudes and fault offset or slip rates are found. The results suggest that the maximum expected earthquake magnitude in the densely populated Marmara–Istanbul region would probably not exceed M7.5. The findings are consistent with available knowledge for the San Andreas Fault and Dead Sea Transform, and can help in estimating hazard potential associated with different sections of large transform faults. [ABSTRACT FROM AUTHOR]

The Erzincan Basin is one of several Neogene sedimentary basins developed by prolonged right-lateral strike-slip along the North Anatolian Fault Zone (NAFZ), the intracontinental transform defining the present boundary between the Eurasian Plate to the north and accreted Anatolian terranes to the south. The basin has a strong asymmetry and young (<780 ka) volcanic centers with widespread development of cross faults defining an advanced phase of pull-apart basin evolution. To isolate faults with no surface geomorphic or morphotectonic signatures in the young sedimentary cover, continuous magnetic profiles were conducted together with detailed interpretation of the regional Bouguer gravity map. This geophysical approach combined with surface mapping defines a fault geometry highlighting a series of buried structures including a fracture system 0.2–2.35 km wide which conforms to the volcanic lineaments seen at the surface. A model is developed for the evolution of the Erzincan Basin with a history commencing as a simple pull-apart by right-lateral strike-slip on the developing NAFZ, probably in Early Pliocene times. Subsequent interaction with a major left-lateral (Ovacık) fault (OF) caused the focus of motion on the NAFZ to shift to the southwest and develop a complex fishbone fracture system. This became the focus of volcanic activity on three lineaments which migrated progressively southwards toward the axis of the basin. Continuing motion on the OF transformed the south east margin of the basin into an extensional zone and the tectonic history of the basin has been further complicated by its proximity to a major transform intersection between the NAFZ and OF. The signatures of recent volcanism and the development of cross faults on which much activity is now concentrated define a mature pull-apart advancing toward extinction. [ABSTRACT FROM AUTHOR]

This study aims to understand the various effects of known tectonism on a fluvial network and to interpret the tectonic deformations using described, and analysed systematic anomalies in the drainage basin of the Yeşilırmak River in northern Turkey at countermarch. This region, which is divided into several faulted wedges by right-lateral strike–slip faulting of the North Anatolian fault zone and its individual splays, has experienced several moderate to large earthquakes with high amounts of surface ruptures during the historical and instrumental periods. The Yeşilırmak River basin includes several geomorphic imprints of such widespread and frequent strike–slip deformations. Offsets (between 750 m and 19 km), aligned drainages, and linear valleys (170 km) are expected geomorphic and tectonic responses to strike–slip faulting in the fluvial system. We used such indicators to determine the long term effects of strike–slip faulting in the Yeşilırmak River drainage network. The measured stream offsets represent decreasing values toward southern splay faults consistent with published geodetic data for the region. However, some other large-scale geomorphic anomalies extracted from the drainage network are not explainable by only strike-slip tectonics. Compressional structures, i.e., anticlines, synclines, in the region are responsible for such large-scale drainage diversions (20–24 km) along the river courses. Although these diversions, the North Anatolian fault zone is the main driving force shaping present geomorphology on a regional scale. The Sungurlu–Ezinepazarı fault also plays a critical role in landscape evolution. Their activities and associated block movements have resulted with tilting processes. On the other hand, the entire fluvial network should be modified by the sea level changes of the Black Sea, particularly in the late Quaternary. [ABSTRACT FROM AUTHOR]