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Imaging the structure of major fault zones is essential for our understanding of crustal deformations and their implications on seismic hazards. Investigating such complex regions presents several issues, including the variation of seismic velocity due to the diversity of geological units and the cumulative damage caused by earthquakes. Conventional migration techniques are in general strongly sensitive to the available velocity model. Here we apply a passive matrix imaging approach which is robust to the mismatch between this model and the real seismic velocity distribution. This method relies on the cross‐correlation of ambient noise recorded by a geophone array. The resulting set of impulse responses form a reflection matrix that contains all the information about the subsurface. In particular, the reflected body waves can be leveraged to: (a) determine the transmission matrix between the Earth's surface and any point in the subsurface; (b) build a confocal image of the subsurface reflectivity with a transverse resolution only limited by diffraction. As a study case, we consider seismic noise (0.1–0.5 Hz) recorded by the Dense Array for Northern Anatolia that consists of 73 stations deployed for 18 months in the region of the 1999 Izmit earthquake. Passive matrix imaging reveals the scattering structure of the crust and upper mantle around the North Anatolian Fault zone over a depth range of 60 km. The results show that most of the scattering is associated with the Northern branch that passes throughout the crust and penetrates into the upper mantle. Plain Language Summary: Investigating the structure of major fault zones is important to understand the deformations of the Earth's crust and their potential impact on future earthquakes. However, the large variations of seismic velocity between different geological units drastically hampers the ability to image those areas. The North Anatolian Fault is no exception since it splits into two branches separating three major geological blocks in the region of the 1999 Izmit earthquake. To image the deep structure of this fault, seismic noise is here exploited to retrieve information on the body waves reflected by the underground heterogeneities. A three‐dimensional map of the subsurface reflectivity is then built by applying methods originally developed in optical microscopy and ultrasound for deep imaging inside complex media. The inner structure of the Earth around the North Anatolian Fault is revealed. In particular, the Northern branch is shown to exhibit a strong damage pattern and a deep penetration inside the upper mantle. Key Points: A matrix approach of passive seismology provides 3D imaging of the North Anatolian Fault, Turkey, over a depth range of 60 kmTransmission matrix between the Earth surface and the underground is extracted by means of spatio‐temporal correlations of seismic noiseTime reversal of this transmission matrix enables a sharp compensation of the seismic velocity variations in the fault area [ABSTRACT FROM AUTHOR]

The M w 7.8 earthquake in Turkey on 6 February 2023 was extraordinary for various reasons. It originated in depth of only 10 km, ruptured along a fault plane around 300 km long and the surface was covered by an extensive network of high-quality seismic instruments. The strong motions resulted in a vast number of tragic casualties and huge material losses in Turkey and Syria. However, abundant and proximate seismic observations of this event and numerous aftershocks give an opportunity to deepen the understanding of earthquake processes. In this study, we carried out an assessment of coseismic changes of seismic velocity using passive image interferometry. We used data from one strong-motion and twenty-four broad-band sensors. We observed coseismic drops of seismic velocity, which reached up to −1.79 per cent at a location directly at the ruptured East Anatolian Fault Zone. Along the M w 7.8 earthquake fault, we observe frequency dependence of the velocity changes. At frequencies above 0.5 Hz, the velocity drops seem to be higher at locations close to the ruptured faults than in the more distant areas. [ABSTRACT FROM AUTHOR]

The Anatolian Plateau, currently experiencing rapid uplift and westward escape, records both the termination of oceanic subduction and the conversion to continental collision. The crustal response to the transition of the subduction environment from eastern to western Anatolia can be inferred by the seismic velocity and attenuation structures. With this study, we construct a broadband Lg‐wave attenuation model for the Anatolian Plateau and use it to constrain lateral crust heterogeneities linked to this transition. Crustal Lg attenuation links late Cenozoic magmatism with asthenospheric upwelling by characterizing the lithospheric thermal structure. The widely distributed strong attenuation observed in eastern Anatolia may be related to the crustal partial melting due to mantle upwelling after the delamination and subsequent break‐off of the Bitlis slab. Lithospheric dripping in central Anatolia likely facilitates the mantle flows through the window between the Cyprus and Aegean slabs, which results in the piecemeal low QLg ${Q}_{\mathit{Lg}}$ anomaly in central Anatolia. Plain Language Summary: Different parts of the Anatolian Plateau are in different evolution stages between oceanic subduction and continental collision and currently undergoing plateau uplift and tectonic escape. The regional seismic velocity and attenuation can be used to characterize crustal partial melting and lateral heterogeneity, which can further identify the underlying subduction process. In this study, we construct a high‐resolution broadband Lg‐wave attenuation model for the Anatolian Plateau. Strong Lg attenuation in Anatolia correlates well with late Cenozoic magmatism distributions and can be an indicator of high temperature or partial melting in the crust. Combined with previous studies, we suggest that the mantle upwelling induced by the delamination of the Bitlis slab is likely reworking the crust in eastern Anatolia and is the cause of widespread thermal anomalies there. The lithospheric dripping process in central Anatolia may facilitate the mantle flows through the window between the Cyprus and Aegean slabs, and results in a piecemeal low QLg ${Q}_{\mathit{Lg}}$ anomaly pattern in central Anatolia. Key Points: A high‐resolution broadband Lg‐wave attenuation model is constructed for the Anatolian PlateauWidespread strong attenuation in the eastern Anatolian crust is likely related to slab delaminationThe circular‐shaped attenuation anomaly may result from slab tearing and lithospheric dripping beneath central Anatolia [ABSTRACT FROM AUTHOR]

The present study investigates azimuthal anisotropy and its relation to the geodynamical processes beneath the back‐arc of the Hellenic subduction zone in the eastern Aegean and western Anatolia where surface tectonics is dominated by the right‐lateral strike‐slip North Anatolian Fault Zone (NAFZ) in the north and E‐W oriented normal fault systems. We obtained apparent SKS splitting parameters from 1,660 good quality and 137 null measurements extracted from 542 events recorded at 40 permanent broadband seismic stations. Overall, the station‐averaged splitting parameters indicate NNE‐SSW oriented fast directions (∼N20°E) and splitting delays around ∼1.5 s. The large splitting delays, particularly observed beneath the northern Aegean can be explained by either an enlarged mantle wedge thickness or increased strength of upper mantle anisotropy. We constrain complex anisotropy structures within two layer models from notable backazimuthal variations in individual splitting measurements observed beneath a few stations at the north located in a close proximity to the NAFZ and central‐western Anatolia. At the western end of the NAFZ, our estimated upper layer anisotropy direction (at ∼120 km) is rather parallel to the NAFZ reflecting the imprint of a lithospheric petrofabric formed by recent deformation while in central‐western Anatolia they correlate well with maximum shear directions and small splitting delays (∼0.6 s) appear to further support relatively thin lithosphere (∼90 km). An overall pattern of extension‐parallel fast directions (N10°E) within lower layer can be attributed to the slab rollback‐induced mantle flow that is highly oblique with respect to the WSW‐ward motion of the Anatolian lithosphere. Plain Language Summary: Seismological constrains on uppermost mantle structures provide essential information for better understanding of the geodynamic processes that have shaped the current deformation in complex tectonic regions. To investigate the seismic anisotropy, which is the directional dependence of seismic wave velocities, and its relation to the geodynamical processes in the upper mantle of eastern Aegean and western Anatolia, we performed splitting measurements on core‐mantle refracted shear waves recorded by 40 permanent broadband seismic stations. We overall estimate NE‐SW oriented fast polarization directions, and delay times between 0.65 and 2.2 s. The results imply that the origin of observed seismic anisotropy can be mostly explained by a combined effect of an internal deformation of the mantle lithosphere and asthenosphere. Our findings reveal the presence of two‐layer anisotropy outlining complicated structures, primarily in the upper mantle of NW Anatolia associated with the western end of North Anatolian Fault Zone. Future numerical modeling and anisotropy studies should be considered to test these results for further interpretation. Key Points: Observed seismic anisotropy can be explained by a combined effect of internal deformation of the mantle lithosphere and asthenosphereThe presence of two‐layer anisotropy is obtained beneath the upper mantle of NW AnatoliaA distinct counter‐clockwise rotation of average fast polarization directions from north to south of the Aegean region is estimated [ABSTRACT FROM AUTHOR]

The noncondensable gases in most geothermal resources include CO2 and smaller amounts of other gases. Currently, the worldwide geothermal power is a small sector within the energy industry, and CO2 emissions related to the utilisation of geothermal resources are consequently small. In some countries, however, such as Turkey and Iceland, geothermal energy production contributes significantly to their energy budget, and their CO2 emissions are relatively significant. SUCCEED is a targeted innovation and research project, which aims to investigate the reinjection of CO2 produced at geothermal power production sites and develop, test, and demonstrate at field scale innovative measurement, monitoring and verification (MMV) technologies that can be used in most CO2 geological storage projects. The project is carried out at two operating geothermal energy production sites, the Kızıldere geothermal field in Turkey and the CarbFix project site at the Hellisheiði geothermal field in Iceland. Together with a brief description of the project, this paper presents the details of the two field sites and the progress made in seismic velocity characterisation and modelling relevant to the Kızıldere geothermal field in Turkey. [ABSTRACT FROM AUTHOR]

Uzungöl settlement and Lake Uzungöl are located in the south of Çaykara, Trabzon, Eastern Black Sea region, and are an important tourist destination in Turkey, with natural beauty and rich flora. However, the settlement and the lake were formed by a historical landslide that covered the front of the Haldizen stream. Residential buildings, tourist facilities, transportation routes, and agricultural activities are located on ground that consists of the material that accumulated from the landslide. In this study, a geophysical investigation using integrated shallow seismic methods was carried out in Uzungöl settlement to provide detailed scientific imaging data on the structure of the subsurface, the physical properties of the soil and rock, the bedrock topography, and the vertical and lateral variation in the landslide deposits. For this purpose, seismic refraction and active and passive multichannel surface wave data were collected from 16 profiles in four separate zones designated according to the agricultural activity and geomorphology of the area. In addition, an electrical resistivity tomography survey of a profile was carried out to determine the reason for low-velocity anomalies such as cavities or man-made voids appearing in P-wave velocity–depth sections and underground water content. After applying basic processes including trace killing/editing, random noise filtering of the data, and amplitude balancing to all seismic data, 2D P-wave velocity–depth sections obtained by tomographic inversion, 1D S-wave velocity–depth profiles, and 2D S-wave velocity–depth sections were generated via analysis of MASW and ReMi data. P- and S-wave velocity–depth sections generally demonstrate three main lithological units in the area: the soil (Vp = 300–600 m/s, Vs = 195–350 m/s and H = 0–2.5 m), the landslide material (Vp = 600–2400 m/s, Vs = 350–680 m/s and H = 2.5–15 m), and the bedrock (Vp > 2400 m/s, Vs > 680 m/s and H ≥ 15 m). In particular, the landslide material exhibits variable thickness from profile to profile and represents the complexity of the subsurface. However, we observed that the deposit thickness increases close to the lake. It was determined that the high seismic velocities of the landslide deposits are attributable to the densely packed deposits and the primarily dry or very poor underground water, according to electrical resistivity tomography results. Moreover, the top of the bedrock is characterized by soft rock, and the deeper part of the bedrock is harder and more compact. We believe that this information will be a useful contribution to geotechnical project development and risk mitigation in the Uzungöl area. [ABSTRACT FROM AUTHOR]

In this study, density, porosity, void ratio, and ultrasonic P- and S-wave first arrival times were measured on limestone, sandstone, and siltstone samples obtained by using mechanical soundings in the city of Zonguldak. Turkey. Fracture and fissure indexes of rocks were calculated from ultrasonic P- (Vp) and S-wave (Vs) velocities. Multi-parameter relationships occurred between ultrasonic velocities with seismic fracture and fissure indexes and physical and mechanical properties of the rocks. Root mean squared error (RMSE = 0.5–0.8%) values correlated between measured densities and densities calculated from Vp and Vs. The correlation coefficients of experimental relations between densities, void ratio, and porosity with seismic velocities that were obtained ranged from 78, 86, 67, and 84%, respectively. Consequently, natural, water-saturated and grain densities, porosity, and void ratio values were determined from new multi-parameter relationships obtained from the combined use of Vp and Vs. In addition, the results of this study suggest that the rock quality may wrongly be determined using the only Vp, whereas it can be obtained more accurately by using Vp and Vs together. The reason for this is that the P wave spreads in solid, liquid, and gas media, while the S-wave spreads only in solid media. Therefore, S-waves will not be altered by fracture filling (gas or liquid), while P-waves are affected by fracture filling. In the present study, the use of Vp and Vs together in relationships was more useful in determining the strength and hydraulic properties of rock mass that the use of either Vp or Vs alone. Also, Rock Quality Designation (RQD) and Rock Mass Rating (RMR) values can be correctly calculated from the combined use of Vp and Vs. As a result, interpretation of crack fill and classification of the rocks can be quickly performed using seismic velocities. [ABSTRACT FROM AUTHOR]

The goal of this study is to establish a workflow for the re-interpretation of almost depleted fields targeting the long-term sustainable oil production; in particular, for the oil fields in Turkey and the neighboring Middle Eastern countries located on the fold and thrust belts of the Zagros Mountains. It also fills some of the gaps in our understanding of the northern part of the Arabian Platform by describing the seismic characteristics of the Cretaceous reservoirs that were deposited during the Aptian to Turonian. The Katin-Barbes oil field (KBOF) in SE-Turkey was used as a case study. In this area, 3D seismic data were used for structural interpretation and re-modeling of Cretaceous carbonates sedimented in the complex tectonic region. The well logs from 55 wells in the field were used to create a compilation of formation tops and were used as reference points for two separate sets of 3-D seismic data, acquired in 1991 and 2017. The quality of seismic data was improved with interpretation filters. The structural model was obtained by using various qualifiers from the seismic cubes and seismic facies changes were identified by analyzing a number of seismic attributes. Therefore, seismic data and velocities from the borehole measurements were combined to form a velocity model in building a structural model. Seismic attributes and well logs were used to create a porosity model. Consequently, top and base of two reservoir units; the Derdere and Sabunsuyu Formations have been clarified and re-defined, and potential new well locations were identified. Depending on the results of this investigation, 9 new wells were drilled in the potential areas in the KBOF, recently. Except the last one drilled on the NE boundary of the northern block, all wells have been completed as the "oil producing wells" and top of the reservoir units were encountered at almost the same depths in our depth model. Therefore, results and proposed methods in this research are confirmed by the real, borehole data. This research will be an examplary study for the re-evaluation of older and/or almost depleted oil fields, either in Turkey or in the other Middle Eastern countries. • This study indicates the seismic characteristics of Aptian to Turonian units on the N of Arabian Platform. • Some innovative steps were indicated in an old HC field after new seismic data. • New drillable locations were determined in this old oil field, KBOF. • The goal of this preliminary study is to establish a framework for long-term oil production in the almost depleted fields. [ABSTRACT FROM AUTHOR]

This paper presents new models of the seismic velocity structure of Eastern Anatolia, Turkey. We applied a local earthquake tomography method to arrival time data produced by local and regional events in Eastern Anatolia to understand the three-dimensional seismic velocity and Vp/Vs models and their correlation with the geological evolution and tectonic processes in the study area. The data are obtained from 78 broadband seismic stations, owned by the Earthquake Department of the Disaster and Emergency Management Presidency, for the period between 2008 and 2017. Seven depth cross sections are taken along various segments of the East Anatolian Fault Zone. Travel times of 53,099 phase readings (29,122 P-phase and 23,977 S-phase picks) from 4249 high-quality earthquake recordings are analysed to develop 3-D Vp (lithological) and Vp/Vs (petrological) models of the study area. The resulting P-wave velocities describe intrusive magmatic bodies, sediment thickness and the structure of the basin. The Vp/Vs structures aid to limit the position of the faults, areas of weakness, and gas- or liquid-saturated units with regions of high pore pressure. Four main seismic crustal layers down to 40 km are determined. The upper crust (0–8 km) has Vp ≤ 4.6 km/s, whereas in the middle crust (~ 9–20 km) a Vp perturbation between 4.6 and 5.8 km/s is observed. In the lower crust (~ 20–35 km), Vp changes from 5.9 to 7.3 km/s and in the upper mantle layer (below 36 km), Vp exceeds 7.4 km/s. In all cases, seismic velocities are well-resolved in the first 40 km. Tomograms are compatible with the geological characteristics of the region. Dominant high P-velocity values are observed beneath the collision zone. Conrad discontinuity is detectable at 20 km depth, while Moho depth is observed to vary between 30 and 40 km in the study area. [ABSTRACT FROM AUTHOR]

We use observations of surface waves in the ambient noise field recorded at a dense seismic array to image the North Anatolian Fault zone (NAFZ) in the region of the 1999 magnitude 7.6 Izmit earthquake in western Turkey. The NAFZ is a major strike-slip fault system extending ∼1200 km across northern Turkey that poses a high level of seismic hazard, particularly to the city of Istanbul. We obtain maps of phase velocity variation using surface wave tomography applied to Rayleigh and Love waves and construct high-resolution images of S-wave velocity in the upper 10 km of a 70 × 30 km region around Lake Sapanca. We observe low S-wave velocities (<2.5 km s -1) associated with the Adapazari and Pamukova sedimentary basins, as well as the northern branch of the NAFZ. In the Armutlu Block, between the two major branches of the NAFZ, we image higher velocities (>3.2 km s -1) associated with a shallow crystalline basement. We measure azimuthal anisotropy in our phase velocity observations, with the fast direction seeming to align with the strike of the fault at periods shorter than 4 s. At longer periods up to 10 s, the fast direction aligns with the direction of maximum extension for the region (∼45 ∘). The signatures of both the northern and southern branches of the NAFZ are clearly associated with strong gradients in seismic velocity that also denote the boundaries of major tectonic units. Our results support the conclusion that the development of the NAFZ has exploited this pre-existing contrast in physical properties. [ABSTRACT FROM AUTHOR]

• Focus on reflection amplitudes for studying the effect of a CO 2 -saturated fracture. • S-wave velocity is more sensitive to changes in pore pressure than P -wave velocity. • Stress-dependency of the P-wave velocity increases with temperature. • Temperature-dependency of the P-wave velocity increases with reducing stress. As part of a seismic monitoring project in a geothermal field, where the feasibility of re-injection and storage of produced CO 2 is being investigated, a P- and S-wave seismic velocity characterisation study was carried out. The effect of axial and radial (up to 42 MPa) stress, pore pressure (up to 17 MPa), pore fluid (100% brine or supercritical CO 2) and temperature (21–100 °C) on seismic properties were studied in the laboratory for the two main reservoir formations at the Kızıldere geothermal reservoir. Each (un)confined compressive strength test performed revealed a similar trend: rapidly increasing velocity at low stresses followed by a more moderate increase at higher stresses. The data implied that the stress-dependency of the velocity increased with temperature. Increasing temperatures resulted in decreasing P-wave velocities due to mineral thermal expansion. This temperature-dependency increased with reducing stress levels. The S-wave velocity seems to be more sensitive to changes in pore pressure than the P-wave velocity. On the other hand, the S-wave velocity is less affected by an increasing axial stress compared to the P-wave velocity. By performing multiple nonlinear regression on the velocity dataset, related to a brine-saturated fractured marble, second-degree polynomial trends were found for the P- and S-wave velocity, as a function of temperature, axial stress, and pore pressure, that can potentially be used for predicting velocities at Kızıldere, or other similar, geothermal site(s). For distinguishing between a 100% brine-saturated versus a fully supercritical CO 2 -saturated fracture, the arrival times of the first arrivals were too close to each other to allow their utilization. The fracture aperture was too small compared to the wavelength of the source signal. However, differences in P- and S-wave amplitudes of the first arrivals were seen, where the supercritical CO 2 -saturated crack revealed consistently lower peak and trough amplitudes compared to the brine-saturated scenario. [ABSTRACT FROM AUTHOR]

In this study, seismic assessment of one story precast industrial buildings that constitute majority of industrial facilities in Turkey was investigated by using probabilistic approach. For this purpose, 98 one story precast industrial buildings that represent general structural aspects of precast industrial building stock of Turkey were used. Strength and deformation capacities of buildings were determined by inelastic methods and seismic demands were calculated by nonlinear time history analyses. In order to represent low, moderate and high intensity earthquake levels, more than 300 ground motion records were used. Fragility curves of precast buildings were then constructed by comparing the displacement capacities and seismic demands. Peak ground velocity was used as ground motion parameter to construct analytical fragility curves. Assessment of inventory buildings was performed by considering the effect of lateral strength ratio, stiffness and ductility parameters. Observations have shown that probabilities of lower damage levels (slight and moderate) are almost similar and they are independent from structural parameters considered. It was also observed that ductility and lateral strength ratios (V/W) have significant effect on seismic fragilities of precast industrial buildings at higher damage levels. Based on the observations, building stock was classified in three groups. Results have shown that strength and ductility based classification of existing precast industrial buildings is quite effective and it can be used as an important tool for the seismic assessment studies of one story precast industrial buildings. [ABSTRACT FROM AUTHOR]

Assessment of potential seismic risk and losses in urban environments is necessary for several purposes ranging from risk mitigation to city and regional planning. It is well known that loss estimation should be performed within an interdisciplinary setting involving earth sciences and engineering. Field experience from recent events worldwide shows that the spatial variability of seismic damage is due to the combined effects of earthquake source properties, local site conditions and structural characteristics. In this study, a scenario-based multi-input damage estimation framework in an urban region was utilized for the Gaziantep city center (southeastern Turkey) that is located in a region of high seismic hazard with no large events in the instrumental era. Initially, a thorough geological and seismo-tectonic assessment of the area was performed followed by estimation of two critical scenario events with moment magnitude (Mw) of 6.5 and 6.6 on nearby active faults. Then, a regional velocity model was compiled from regressions of existing regional geotechnical and seismic data in terms of the V S30 parameter. As the next step, field surveys for the assessment and classification of buildings in the study area were performed followed by vulnerability analyses. As the last step, the mean damage ratios were computed at 198 neighborhoods within the city center. The results indicate not only a high hazard but also high risk in the Gaziantep area due to the combination of close proximity to the faults along with local site effects and building fragilities. • Identification of seismic source characteristics of Gaziantep city, Turkey. • Development of regional seismic velocity model. • Simulation of ground motion records for the selected scenario earthquakes. • Identification of building stock characteristics in the study area and derivation of seismic fragility curves for each building typology. • Estimation of regional seismic damage. [ABSTRACT FROM AUTHOR]

Highlights: [•] New Moho depth map is presented. [•] Crustal thickness is varying between 24 and 48km. [•] The thinnest crust observed at the western coast of Anatolia. [•] The thickest crust observed at the eastern Anatolia. [•] Uppermost mantle S-wave speed is lower than world average. [ABSTRACT FROM AUTHOR]

In ground motion simulation studies based on earthquake rupture scenarios, the absolute ground motion level, frequency content, signal duration and distribution of simulated ground motion is highly dependent on the input parameters used in the calculations. We conduct a predictive study assessing the potential ground motions for İzmir, Turkey based on earthquake scenarios. We calculate ground motions from a reference scenario (Mw6.8) and compare it to 25 test scenarios for the İzmir fault in order to investigate the effect of input parameter uncertainty on the simulated ground motion. In this study, we use a hybrid broadband frequency (0.1-10 Hz) ground motion simulation technique. We find average ground motion levels in the central area of İzmir of more than 600 cm/s and 60 cm/s for peak ground acceleration and velocity, respectively, while the standard deviation is found to exceed 200 cm/s and 20 cm/s, respectively. The tested parameters identified to have the largest influence on the absolute ground motion level are seismic moment, average stress-drop, rise time and rupture velocity. Parameters identified to have the least effect on ground motion level are rake and ratio of stress-drop on asperities to background stress-drop. The low-frequency ground motion, critical in terms of damage to the building stock in İzmir, is mostly affected by the location of nucleation point, seismic moment, depth of the rupture area, rise time and the velocity model. It is, therefore, highly recommended that future studies focus on reducing the uncertainties in these input parameters. [ABSTRACT FROM AUTHOR]

Abstract: We present results on imaging contrast of seismic velocities across the Mudurnu segment of the North Anatolian Fault Zone (NAFZ) in northwestern Turkey with polarization analysis of early P waveforms generated by near-fault seismicity and recorded by near-fault stations. The analysis uses changes in motion polarity from fault–normal to source–receiver directions to identify early-arriving fault zone head waves on the slow side of the fault, and measure the arrival times of the head and direct P waves. The moveout between the head and direct waves with increasing source–receiver distance along the fault provides an estimate of the average contrast of seismic velocities across the fault. The results indicate that the average contrast of P wave velocities across the Mudurnu segment of the NAFZ is at least 6%, with the south block being the faster side. The findings provide a basis for deriving improved event locations, focal mechanisms and estimated shaking hazard associated with earthquakes on the fault. The analysis technique can be used in other fault zones monitored with sparse seismic instrumentation. [Copyright &y& Elsevier]

SUMMARY As a part of the DEad Sea Integrated REsearch (DESIRE) project a near-vertical incidence reflection (NVR) experiment with a profile length of 122 km was completed in spring 2006. The profile crossed the southern Dead Sea basin (DSB), a pull-apart basin due to the strike-slip motion along the Dead Sea Transform (DST). The DST with a total displacement of 107 km since about 18 Ma is part of a left-lateral fault system which connects the spreading centre in the Red Sea with the Taurus collision zone in Turkey over a distance of about 1100 km. The seismic experiment comprises 972 source locations and 1045 receiver locations. Each source was recorded by ∼180 active receivers and a field data set with 175 000 traces was created. From this data set, 124 444 P-wave first-break traveltimes have been picked. With these traveltimes a tomographic inversion was carried out, resulting in a 2-D P-wave velocity model with a rms error of 20.9 ms. This model is dominated by a low-velocity region associated with the DSB. Within the DSB, the model shows clearly the position of the Lisan salt diapir, identified by a high-velocity zone. A further feature is an unexpected laterally low-velocity zone with P-velocities of 3 km s-1 embedded in regions with 4 km s-1 in the shallow part on the west side of the DSB. Another observation is an anticlinal structure west of the DSB interpretated to the related Syrian arc fold belt. [ABSTRACT FROM AUTHOR]

The eastern Pontides orogenic belt is one of the most complex geodynamic settings in the Alpine-Himalayan belt due to the lack of systematical geological and geophysical data. In this study, 1D crustal structure and P-wave velocity distribution obtained from gravity modeling and seismological data in the area has been used for the development of the thermal model of the eastern Pontides orogenic belt. The computed temperature-depth profiles suggest a temperature of 590 ± 60°C at a Moho depth of 35 km indicates the presence of a brittle-ductile transition zone. This temperature value might be related to water in the subducted crust of the Tethys oceanic lithosphere. The Curie temperature depth value of 29 km, which may correspond to the crustal magma chambers, is found 5-7 km below the Moho depth. Surface heat flow density values vary from 66.5 and 104.7 mW m. High mantle heat flow density value of 48 mW m is obtained for the area should be related to melting of the lithospheric mantle caused by upwelling of asthenosphere. [ABSTRACT FROM AUTHOR]

For Anatolian earthquakes, there are insufficient strong motion data from rock sites to model an attenuation relationship for Turkey. This necessitates the use of records from soil sites, which are significantly affected by amplification. In order to include soil site data in the attenuation analyses, boreholes were drilled at 64 recording stations on soil sites. After removing the effects of soil amplification, rock site and soil site data were combined to establish an attenuation relationship. Various models were tested through regression analyses using moment magnitude, epicentral distance and threshold peak horizontal ground acceleration. A new attenuation relationship is modeled for Turkey. [ABSTRACT FROM AUTHOR]

Inversion of Pn traveltime residuals from a 39-station broad-band array provides a high-resolution image of the velocity structure in the uppermost mantle beneath central Turkey. Individually picked Pn phase arrivals from events recorded by the North Anatolian Fault Passive Seismic Experiment and the Kandilli Observatory were combined with additional events associated with the Eastern Turkey Seismic Experiment. Tomography results show no change in Pn velocity across the North Anatolian Fault, although longitudinal variations are evident. A region of very low Pn velocities (<7.8 km s−1) is imaged east of the Central Anatolian Fault Zone (CAFZ), with a transition to faster velocities (>8.1 km s−1) west of the fault. The sharp transition along the CAFZ, which follows the palaeotectonic Inner-Tauride Suture, may represent the location of the edge of the slab window, created when the oceanic slab broke off along the Bitlis-Zagros Suture around 11 Ma, as the Arabian plate collided with the Eurasian plate. [ABSTRACT FROM AUTHOR]

Abstract: This study investigates an application of genetic programming (GP) for the prediction of peak ground acceleration (PGA) using strong-ground-motion data from Turkey. The input variables in the developed GP model are the average shear-wave velocity, earthquake source to site distance and earthquake magnitude, and the output is the PGA values. The proposed GP model is based on the most reliable database compiled for earthquakes in Turkey. The results show that the consistency between the observed PGA values and the predicted ones by the GP model yields relatively high correlation coefficients (R 2=0.75). The proposed model is also compared with an existing attenuation relationship and found to be more accurate. [Copyright &y& Elsevier]

Abstract: Waveforms of 50 teleseismic receiver functions and dispersion curves have been used to invert jointly for the 1D average crust and uppermost mantle seismic structure beneath GEOFON station ISP. The surface wave (Rayleigh and Love) dispersion curves were adopted from an earlier study and greatly help to stabilize the inversions by alleviating the deficiencies of inverting the receiver functions alone. The teleseismic receiver functions had a backazimuth distribution from which three stacks were created. All the stacks resulted in compatible inversions. Nine different influence factors ranging between 0.1 and 0.9 were employed and the influence factors around 0.5 were preferred for producing a reasonable seismic structure to represent the geology under station ISP. Three distinct crustal depth ranges are identified based on the inverted velocity-depth profile. The first corresponds to 0–5km where the velocity-depth profile has a positive gradient with an increase from 2.5kms−1 to 3.0kms−1. The second depth range is 5–10km and the velocity-depth profile shows a positive gradient between 3.0kms−1 and 3.20kms−1. A velocity jump from 3.20kms−1 to 3.62kms−1 tops the third depth range (10–20km), which is characterized by a constant velocity. There is another velocity drop at 20km depth from 3.62kms−1 to 3.40kms−1 and the low velocity therein is persistent down to 27.5km. Below this depth range, the shear velocity increases until 40km depth where the Moho discontinuity is estimated with Sn velocity of 4.4kms−1. In general, seismic velocities under SW Anatolia are considerably slower than those of the Preliminary Reference Earth Model (PREM). [Copyright &y& Elsevier]

Beside of measuring thermal conductivity of rocks directly, this study aims to measure thermal conductivity values from P wave velocities indirectly. The P wave velocities of the study area, in the NW of Isparta city, determined by seismic profiles were used to compute thermal conductivity values. Thermal conductivity contour map of the study area was created by this computed thermal conductivity values. When the maps of P wave velocity and thermal conductivity are examined, both the low thermal conductivity and low P-velocity contours were observed in the southern part of the study area. It was thought that the area characterized by lower thermal conductivity and velocities might be prevent astenospheric heat flow not to reach at the surface. As a result, the complex deformational crust of the study area has a style colder than the extensional crust of the western Anatolia. [ABSTRACT FROM AUTHOR]

The northwestern part of Turkey is a significant area for its location on the accretionary region of several micro-continents and blocks. Therefore, there are several suture zones and western segments of the "North Anatolian Fault Zone" are scattered in the study area. Due to trans -tensional stresses, there are several pull-apart basins and/or depressions within the fault zone in the study area. As a consequence, it is also possible to observe magmatic intrusions into the fault segments. All these events and magmatic emplacements in the tectonic framework provide significant magnetic anomalies throughout the region. In this study, geothermal potential of the region is investigated based on the spectral analysis of the magnetic data, together with the seismic velocity (VP) distribution in the area using the log-linear relationship between the seismic velocity and the radiogenic heat production. Although two regions are emerging in the Curie Point Depth (CPD) and geothermal gradient maps, only one anomalous area from Bursa to Tekirdag may be considered as a promising region for the further geothermal energy exploration in the heat-flow maps prepared according to two different thermal conductivity coefficients. Seismic velocities are also low in this anomalous region decreasing down to 6.40 km/s around the shoreline of Tekirdag. Heat-flow values are increasing up to 110 mW/m2 in this particular area where the CPDs are around 14 km. [Display omitted] • CPDs are in the range of 14–16 km between Bursa and Tekirdag, in the Marmara region. • Geothermal gradient anomaly around Tekirdag is represented with 39 °C/km contours. • Seismic velocities decreased down to 6.40 km/s in this thermally anomalous area. • Heat-flows are around 100–110 for thermal conductivity coefficients (2.5 and 2.7). • Radiogenic heat production increases up to 0.36 (μ W m − 3 ) in the anomalous zone. [ABSTRACT FROM AUTHOR]

Here, we investigated the crustal structure beneath eastern Anatolia, an area of high seismicity and critical significance for earthquake hazards in Turkey. The study was based on the local tomography method using data from earthquakes that occurred in the study area provided by the Turkiye Cumhuriyeti Ministry of Interior Disaster and Emergency Management Directorate Earthquake Department Directorate of Turkey. The dataset used for tomography included the travel times of 54,713 P-waves and 38,863 S-waves from 6355 seismic events. The distributions of the resulting seismic velocities (Vp, Vs) down to a depth of 60 km demonstrate significant anomalies associated with the major geologic and tectonic features of the region. The Arabian plate was revealed as a high-velocity anomaly, and the low-velocity patterns north of the Bitlis suture are mostly associated with eastern Anatolia. The upper crust of eastern Anatolia was associated with a ~10 km thick high-velocity anomaly; the lower crust is revealed as a wedge-shaped low-velocity anomaly. This kind of seismic structure under eastern Anatolia corresponded to the hypothesized existence of a lithospheric window beneath this collision zone, through which hot material of the asthenosphere rises. Thus, the presented results help to clarify the deep structure under eastern Anatolia. [ABSTRACT FROM AUTHOR]

Mt. Hasan (3262 m) is the second highest stratovolcano in Central Anatolia, Turkey, and is considered active based on a ca. 9 ka explosive summit eruption that was arguably depicted in a Neolithic mural at the nearby Çatalhöyük archaeological site. Besides evidence for Holocene activity of Mt. Hasan, its eruptive chronostratigraphy and hazard potential remain poorly constrained. Here, we apply (U–Th)/He thermochronology in combination with U–Th–Pb crystallization ages (zircon double-dating), including a novel population-based approach to disequilibrium correction of (U–Th)/He data, in an attempt to determine the eruption ages of strategically sampled lavas and pyroclastic deposits and to refine the Late Pleistocene chronostratigraphy of Mt. Hasan. During the Late Pleistocene, Mt. Hasan erupted multiple interfingering andesitic lava flows along with block-and-ash-flows. Seven of these lava flows, typically the stratigraphically youngest in a particular segment around the two central vents of the volcano, yielded Late Pleistocene eruption ages between 91.9 ± 3.9 and 18.1 ± 2.4 ka (uncertainties stated at 1σ). An even younger block-and-ash-flow was deposited on the western flank of the volcano at 13.5 ± 1.5 ka, which together with a ca. 9 ka small-volume explosive summit eruption define the youngest activity at the main edifice of Mt. Hasan. Collectively, these data indicate a Late Pleistocene recurrence of at least one eruptive phase every ca. 5–15 ka. New volume estimates for the Quaternary edifice of ~130–180 km3 translate into an integrated long-term eruptive magma flux of ~0.3 km3/ka, which is just slightly higher than Late Pleistocene flux estimates based on lava flow geochronology and volumes determined by analysis of digital elevation models. This long-term eruptive flux estimate is similar to those of stratovolcanoes in continental arcs, indicating that eruptive productivity in post-collisional settings can match that of active continental margins. All Mt. Hasan eruptions, including the Holocene event, sampled zircon which crystallized coeval with earlier eruptive phases, indicating longevity of the magma plumbing system. Along with ongoing fumarole activity and evidence for mid-crustal low seismic velocity zones, this suggests that a subvolcanic magma reservoir remains active to the present day. Unlabelled Image • New population-based disequilibrium corrections improved (U–Th)/He age accuracy. • Late Pleistocene recurrence of at least one eruptive phase every 5–15 ka at Mt. Hasan. • Eruptive fluxes presented as differential volumes vs. ages to accent recent trends. • Long- and short-term fluxes of post-collisional volcanism similar to arc settings. • Protracted zircon crystallization supports Mt. Hasan as an active volcanic center. [ABSTRACT FROM AUTHOR]

Seismic waves are commonly used to investigate how the soils behave during the earthquake. The goal of this study is to predict the porosity of shallow clay soils from seismic wave velocities investigated the dynamic properties of the soil and to develop the porosity graphs depending on geotechnical properties of the soils. The parameters used to determine porosity are compressional (P) and shear (S) wave velocities, seismic velocity ratio, Poisson ratio, bulk modulus, shear modulus. This study calculates bulk modulus, shear modulus and Poisson ratio from P- and S-wave velocities obtained by using the seismic-refraction method, and porosity values using grain and dry densities of core samples obtained from several boreholes within the study area. The study area is located in western Turkey, and has predominantly clay-silt-sand-gravel deposits. The data of the clay soils within the area were separately arranged based on the values of the Poisson ratio, seismic P wave velocity, seismic velocity ratio (Vp/Vs) and the stiffness of the clay soils. Using these parameters, new multi-parameter relationships were established among shear modulus, Poisson ratio, seismic velocities and porosity of clay soils. The errors of the parameters used for each relationship were determined using the error norm technique. According to the results of the error norm technique, the shear wave velocity and shear module have lowest error for estimating porosity. Consequently, the proposed relationships are recommended to estimate porosity of shallow clay soils. These relationships, in addition to estimate the porosity of clay soil, can be interpreted whether the liquid and/or gas saturation of pores of this soil. Also, the experimental results show that if the ratio of Vp/Vs < 1.53, the pores spaces of the clay soil are filled with gas. • P- and S-wave velocities were obtained from the seismic-refraction method. • Elastic parameters and Poisson ratio were calculated from seismic velocities. • Porosity values were obtained from grain and dry unit weights of core samples • Relationships were newly established among shear modulus, Poisson ratio, seismic velocities and porosity of clay soils • The errors of dynamic parameters to estimate the porosity of clay soils were determined depending on error norm technique. [ABSTRACT FROM AUTHOR]

In this study we present the results of an ongoing 3D full-waveform inversion for theArabian-Eurasian collision zone in eastern Turkey and Iran. This is intended to extract asmuch information as possible from available seismograms in order to constrain seismicstructure in both the crust and the upper mantle. In our method we simulate the 3D visco-elastic wavefield using the newly developedspectral-element solver Salvus. Our numerical mesh honors topography of the surface andinternal discontinuities. We compare observed and synthetic waveforms using time frequencyphase misfits. Using adjoint techniques, we then compute sensitivity kernels with respect tothe model parameters, which are VSV, VSH, VPV, and VPH. Finally, the kernels enable theiterative solution of the nonlinear inverse problem with the help of the L-BFGSalgorithm. For this study we obtained seismic waveform data of 143 earthquakes within themagnitude range of Mw 4.5 to 6.3 that occurred in the region between 2012 and 2016. Theseevents were recorded by 271 broadband seismic stations belonging to the two nationalIranian networks and freely available seismic stations of the Turkish Network, madeavailable by IRIS. For data management and workflow organisation we employ theLarge-Scale Seismic Inversion Framework (LASIF), modified to operate with theAdaptable Seismic Data Format (ASDF), which facilitates simulations on large HPCclusters. Starting from the first generation of the Collaborative Seismic Earth Model, we firstconstrain longer-wavelength structure. To this end, we consider 3-component recordingsfrom a subset of 41 events in the period range from 50 to 80 s. This period range issuccessively broadened to include shorter periods; for instance, the lower end of theperiod range was meanwhile extended to 35 s. For each period band, the number andthe length of measurements are increased to ultimately comprise almost completeseismograms, and also the number of events is increased to use complete of dataset. [ABSTRACT FROM AUTHOR]