In 2010, project CoCoCo (incipient COntinent-COntinent COllision) recorded a 650km long amphibian N-S wide-angle seismic profile, extending from the Anatolian plateau across southern Turkey and Cyprus to just south of the Eratosthenes Seamount (ESM). The aim of the project is to reveal the impact of the transition from subduction to continent-continent collision of Africa with Anatolia. Arrival picking, finite-differences ray-tracing and inversion of the offshore and on-offshore data produced a tomographic model across southern Cyprus, the accretionary wedge and the ESM. The main features of this model are (1) crustal P-velocities predominantly lower than 6.5km/s beneath the ESM, (2) crustal thickness between 28 and 37km, (3) an upper crustal reflection at 5km depth beneath the ESM, (4) the likely presence of oceanic crust south of the ESM and a transform margin north of it and (5) a 12km thick ophiolite sequence on Cyprus. Land shots on Turkey, also recorded on Cyprus, gravity data and geological and previous seismic investigations allow to derive a layered velocity model beneath Anatolia and the northern part of Cyprus. The main features of this model are (1) Moho depths of 38–45km beneath the Anatolian plateau, (2) an upper and lower crust with large lateral changes in velocity and thickness, (3) a north-dipping subducting plate below Cyprus with a steepening of the dip-angle of the plate at about 45km depth. Thus, the wide-angle seismic and gravity data provide detailed insights into the 2-D geometry and velocity structures associated with the Cyprus Arc collision zone. Finally, integrated analysis of the geophysics and geology allows a comprehensive interpretation of the crustal structure related to the collision process.

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

In order to investigate crustal structure beneath the eastern Marmara region, a seismic refraction survey was conducted across the North Anatolian Fault (NAF) zone in north west Turkey. Two reversed profiles across two strands of the NAF zone were recorded in the Armutlu Highland where a tectonically active region was formed by different continents. We used land explosions in boreholes and quarry blasts as seismic sources. A reliable crustal velocity and depth model is obtained from the inversion of first arrival travel times. The velocity-depth model will improve the positioning of the earthquake activities in this active portion of the NAF. A high velocity anomaly (5.6–5.8 km s−1) in the central highland of Armutlu block and the low velocity (4.90 km s−1) pattern north of Iznik Lake are the two dominant features. The crustal thickness is about 26 ± 2 km in the north and increases to about 32 ± 2 km beneath the central Armutlu block in the south. P-wave velocities are about 3.95 km s−1 to 4.70 km s−1 for the depth range between about 1 km and 5 km in the upper crust. The eastern Marmara region has different units of upper crust with velocities varying with depth to almost 8 km. The high upper crust velocities are associated with Armutlu metamorphic rocks, while the low velocity anomalies are due to unconsolidated sedimentary sequences. The western side of Armutlu block has complex tectonics and is well known for geothermal sources. If these sources are continuous throughout the portions of the crust, it may be associated with a granitic intrusion and deformation along the NAF zone. That is, the geothermal sources associated with the low velocity may be due to the occurrence of widespread shear heating, even shear melting. The presence of shear melting may indicate the presence of crustal fluid imposed by two blocks of the NAF system.

We study the crustal structure of eastern Marmara region by applying the receiver function method to the data obtained from the 11 broad-band stations that have been in operation since the 1999 Izmit earthquake. The stacked single-event receiver functions were modelled by an inversion algorithm based on a five-layered crustal velocity model to reveal the first-order shear-velocity discontinuities with a minimum degree of trade-off. We observe crustal thickening from west (29-32 km) to east (34-35 km) along the North Anatolian Fault Zone (NAFZ), but we observe no obvious crustal thickness variation from north to south while crossing the NAFZ. The crust is thinnest beneath station TER (29 km), located near the Black Sea coast in the west and thickest beneath station TAR (35 km), located inland in the southeast. The average crustal thickness and S-wave velocity for the whole regions are 31 +/- 2 km and 3.64 +/- 0.15 km s(-1), respectively. The eastern Marmara region with its average crustal thickness, high heat flow value (101 +/- 11 mW m(-2)) and with its remarkable extensional features seems to have a Basin and Range type characteristics, but the higher average shear velocities (similar to 3.64 km s(-1)) and crustal thickening from 29 to 35 km towards the easternmost stations indicate that the crustal structure shows a transitional tectonic regime. Therefore, we conclude that the eastern Marmara region seems to be a transition zone between the Marmara Sea extensional domain and the continental Anatolian inland region.

A 29-station temporary broadband PASSCAL network was operated from late October 1999 to August 2001 in eastern Turkey in order to decipher the geodynamics of one of the youngest continent-continent collision zones in the world. This paper focuses on the hypocentral distribution of local earthquakes located during the operation of the network and provides new insights into the active faulting in the Anatolian plateau. A total of 1165 earthquakes were located and classified into four different categories based on the reliability of the locations as established by the data coverage. The accuracy of the locations ranked in the best two categories is estimated to be less than approximately 5 km. The results show that seismic activity in Eastern Turkey is higher than previously documented and there were no subcrustal earthquakes beneath the Arabian-Eurasian collision zone or beneath the Anatolian plateau during our deployment. This result suggests no or very little underthrusting of the Arabian plate beneath Eurasia. Our results also suggest that the North Anatolian Fault zone extends farther toward the southeast, well beyond the Karliova triple junction, and that a number of unmapped active, seismogenic faults exist in the region. We also observed a possible difference in the seismogenic thickness of the East Anatolian fault zone (EAFZ) and the North Anatolian fault zone (NAFZ).

Two sets of calibration shots are planned in Turkey in 2002 and 2003 for the calibration of regional seismic stations and to improve knowledge of earth models in the region. The shots will be at Keskin in central Turkey, and at Lake Van in eastern Turkey. Keskin is where the short-period array of the Belbasi Station is located. Belbasi Station comprises a long-period array located in Ankara, and the aforementioned short-period array located in Keskin. The Keskin short-period array is designated as an International Monitoring System (IMS) station (PS43). The primary objectives of the experiments are: (1) calibrate the regional travel times and propagation characteristics of seismic waves across the Middle East and Eastern Mediterranean region; (2) calibrate local and regional models for specific IMS stations in Turkey; (3) conduct a reciprocal experiment to provide dense local and near regional calibration of the Keskin Belbasi IMS array in Turkey; and (4) provide data to enhance IMS detection, location, and discrimination capabilities. The first calibration shot (two tons of explosives in boreholes) will be conducted near Keskin in October 2002. We expect that the shot will be recorded within a radius of about 500 km. It will provide reciprocal calibration for the nearby Keskin short-period array, Incorporated Research Institutes in Seismology (IRIS) station ANTO, and the long-period Belbasi array. In this paper we present detailed three dimensional (3-D) crustal models of the region, calculated travel times, and synthetic seismograms. Well located (GT-5) local and regional earthquakes around the Keskin array are identified and areas of anticipated seismic activity will be instrumented. The information will guide the deployment of stations for the recording of the Keskin shot, and expedite the analysis of the data.

To upgrade local crust models and estimate site-specific station corrections (SSSCS) for more accurate hypocenter location, a number of controlled quarry blasts (GT0) were recently conducted in the Marmara Sea region, close to the Izmit earthquake (17 August 1999). Both the blasts and well-constrained aftershocks (GT5) were recorded by the KOERI network and TUBITAK stations in Turkey. The blasts were located using arrival times and two 1-D crustal models: 1) the KOERI model for regional location; 2) a modified model from refraction profiles. Improvement was achieved by using model 2 and VELEST, an optimization procedure. The improved models were used to relocate selected Izmit aftershocks. Relocation experiments, including calculation of the hypocenter ellipsoid and Monte-Carlo simulation, were performed to verify accuracy and reliability of new hypocenter estimations. We continued the program of calibration explosions in Israel, conducting a series of controlled quarry blasts to the North of the Sea of Galilee, including a 25-ton shot to complement the 2002 Rotem explosion in the Negev desert, providing better signal observations in Cyprus, Lebanon, Syria and Turkey. The closely spaced (~50 km) 1999 Dead Sea and 25-ton Rotem calibration explosions were recorded at the same stations in Israel, Jordan, Cyprus and Saudi Arabia, providing observations for similar propagation paths. The data enabled an analysis of the influence of different sources on amplitudes, waveform and spectral content of regional phases. The calibration explosions, located in the Dead Sea fault zone, provided a variety of results in the context of nuclear test monitoring: a) accurate travel time corrections for regional phases relative to IASPEI91 and GII models at stations of local networks and the International Monitoring System (IMS), b) verification and improvement of velocity models, c) estimation of attenuation and magnitude-yield relations, d) characterization of new seismic sources and local mining practices, and multi-station discrimination analysis. We provided a pilot performance analysis for a new IMS array on Mt. Meron, Israel (MMAI or AS49), operational in January 2003. The 16-element small aperture array is equipped with broadband Gurlap seismometers placed in deep (50 -100 m) boreholes. The MMAI detectability and signal parameter estimation was analyzed by the standard and adaptive beamforming techniques using data from the recent controlled quarry explosion series in Israel and regional GT5 earthquakes. New robust beamforming techniques have been developed and applied to the array data, showing promising results for enhancing monitoring capabilities in the region. The 2Dtracerdn software was used to compute SSSCs of the Pg, Pn, P, Sg, Sn, S phases for the eight stations: EIL, MRNI, BRAR, DAVOS, KVAR, MLR, GERESS and OBN, using the 3D velocity model CUB1.0. For stations EIL, MRNI and BRAR we have computed SSSCs in the direction of small areas in Cyprus and Turkey (Izmit, Duzce and Adana), containing selected Ground Truth (GT0-GT5) sources. The results have been compared to the observed deviations between the measured and IASPEI91 travel times from the ground-truth (GT) events.

The crustal structure of the Anatolian plateau in Eastern Turkey is investigated using receiver functions obtained from the teleseismic recordings of a 29 broadband PASSCAL temporary network, i.e., the Eastern Turkey Seismic Experiment [ETSE]. The S-wave velocity structure was estimated from the stacked receiver functions by performing a 6-plane layered grid search scheme in order to model the first order features in the receiver functions with minimum trade-off. We found no significant crustal root beneath the western portion of the network, but there is some evidence of crustal thickening in the northern portion of the network. We found an average crustal thickness of 45 km and an average crustal shear velocity of 3.7 km/s for the entire eastern Anatolian plateau. Within the Anatolian plateau we found evidence of a prominent low velocity zone where the crust thickness is approximately 46 km. These results suggests that the 2 km high topography across the Anatolian plateau is dynamically supported because most of the plateau appears to be isostatically under-compensated. Also, there appears to be a region of thin crust at the easternmost edge of the Anatolian plateau that may be a relic from the accretion of island arcs to the Eurasian plate.

Observationsbased on relatively limited data recorded by sparsely distributed stations have indicated that regional seismic phase propagation(LgandSn)is very complex in the Middle East. Accurate characterization of regional seismic wave propagation in this region necessitates the use of a large number of seismic stations. We have compiled a large data set of regional and local seismograms recorded in the Middle East. This data set comprises approximately four years of data from national short-period networks in Turkey and Syria, data from temporary broadband arrays in Saudi Arabia and the Caspian Sea region, and data from GSN, MEDNET, and GEOFON stations in the Middle East. We have used this data set to decipher the character and pattern of regional seismic wave propagation. We have mapped zones of blockage as well as inefficient and efficient propagation forLg Pg andSnthroughout the Middle East. Two tomographic techniques have been developed in order to objectively determine regions of lithospheric attenuation in the Middle East. We observe evidence of major increase inLgattenuation, relative toPgacross the Bitlis suture and the Zagros fold and thrust belt, corresponding to the boundary between the Arabian and Eurasian plates. We also observe a zone of inefficientSnpropagation along the Dead Sea fault system which coincides with lowPnvelocities along most of the Dead Sea fault system and with previous observations of poorSnpropagation in western Jordan. Our observations indicate that in the northern portion of the Arabian plate (south of the Bitlis suture) there is also a zone of inefficientSnpropagation that would not have been predicted from prior measurements of relatively lowPnvelocities. Mapped high attenuation ofSncorrelates well with regions of Cenozoic and Holocene basaltic volcanism. These regions of uppermost mantle shear-wave attenuation most probably have anomously hot and possibly thin lithosphere.