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The analysis of hydroacoustic signals originating from marine volcanic activity recorded by a remote hydroacoustic (HA) station, HA11 at Wake Island, of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) International Monitoring System (IMS) is presented in this study. The events studied pertain to an eruption series at Kadovar Island, Papua New Guinea during the period January to February 2018. Local visual observations determined that the Kadovar volcano began to erupt at the summit of the island, and then created new vent spots near the coast. The events included the collapse of a lava dome on 9 February 2018. Directions-of-arrivals of the hydroacoustic signals detected at HA11 were evaluated using a cross-correlation technique, this allowed discrimination between hydroacoustics signals originating from the Kadovar volcanic activity and other numerous hydroacoustic signals generated by general seismic activity in the Pacific. Discrimination between volcanic activity and seismicity was achieved by examining the time-frequency characteristics of the hydroacoustic signals, i.e. associating short duration broadband bursts with volcanic eruptions, in line with criteria generally applied for such events. Episodes of high volcanic activity with as many as 80 detections per hour were identified on two occasions, separated by a one-month period of relative quiet. Some of the hydroacoustic signals were characterized by broadband frequency content and high received levels (i.e. ca. 30 dB higher than the ocean microseismic background). It was found that corresponding non-hydroacoustic signals could not be identified by other regional IMS stations, this providing an indication of the likely submarine origin of these events. Long duration bursts recorded on the day when the lava dome collapsed have been identified and characterized in time-frequency space. This study provides a further example of the added value of CTBT IMS hydroacoustic station remote monitoring of marine volcanic events.

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We invert the present day states of stresses for five apparent earthquake clusters in the Northern branch of the North Anatolian Fault in the Sea of Marmara. As the center of the Sea of Marmara is prone to a devastating earthquake within a seismic gap between these selected clusters, sensitive analyses of the understanding of the stress and strain characteristics of the region are all-important. We use high quality P and S phases, and P-wave first motion polarities from 398 earthquakes with ML ≥ 1.5 using at least 10 P-wave first motion polarities (FMPs), and a maximum of 1 inconsistent station, obtained from a total of 105 seismic stations, including 5 continuous OBSs. We report here on large numbers of simultaneously determined individual fault plane solutions (FPSs), and orientations of principal stress axes, which previously have not been determined with any confidence from the basins of the Sea of Marmara and prominent fault branches. We find NE–SW trending transtensional stress structures, predominantly in the earthquake clusters of the Eastern Tekirdag Basin, Eastern Cinarcik Basin, Yalova and Gemlik areas. We infer that a dextral strike-slip deformation exist in the Eastern Ganos Offshore cluster. Furthermore, we analyze FPSs of four ML ≥ 4.0 earthquakes, occurred in seismically quiet regions after 1999 Izmit earthquake. Stress tensor solutions from a cluster of small events that we have obtained, correlate with FPSs of these moderate size events as a demonstration of the effectiveness of the small earthquakes in the derivation of states of local stresses. Consequently, our analyses of seismicity and large numbers of FPSs using the densest seismic network of Turkey contribute to better understanding of the present states of the stresses and seismotectonics of the Sea of Marmara.

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

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

We relocate 27 small earthquakes and invert the state of stress in the East of the Central Marmara basin through re-identification of P and S phases using a joint data set. Also, we derive relative locations of 425 clustered earthquakes with ML ≥ 1.5 in the Marmara Region using the Hypodd software. The main objective is to achieve the definition of geometrical orientations and seismic behaviours of the fault segments. Locating between the 1912 Murefte and 1999 Izmit earthquakes and being a seismic gap, seismic and geodetic analyzes in the Central Marmara Sea are significant. We use well-defined P and S phases for locations, and completely observable P-wave first motion polarities (FMPs) for simultaneously determined individual fault plane solutions (FPSs) and stress orientations. We get data from 105 seismic stations, including 5 continuous OBSs; hence, each FPS has at least 10 FMPs and maximum 1 inconsistent station. We observe normal and oblique focal mechanism solutions, and a NE-SW trended extensional state of stress in the Eastern Central Marmara by this comprehensive research, although the main Marmara Fault, the western branch of the North Anatolian Fault Zone (NAFZ), is dominated by a right lateral strike-slip regime. Due to the use of a dense network, we observe neither horizontal nor vertical large shifts in the locations of earthquakes: a total of 398 out of 425 are from Korkusuz Ozturk et al. (Tectonophysics 665:37–57, 2015), after the relative relocation process. As a result, we could not observe fault dip angles clearly, but define seismic zones for each segment which has not been done before for many segments in the Sea of Marmara, and interpret current stress loads. Consequently, our sensitive relocations and stress tensor inversion analyses will make an important contribution to a better understanding of the fault movements in the Sea of Marmara, and shed light on especially earthquake rupture and tsunami analyses.

The dynamic rupture process and near-source ground motion of the 1999 Mw 7.1 Duzce Earthquake are simulated. The fault rupture is governed by the slip-weakening friction model coupled to a three-dimensional viscoelastic wave equation. The problem is solved numerically by a 3-D dynamic rupture code that uses a generalized finite difference method. Initial parameterization of stress drop (Delta tau) and strength excess (S-e) for dynamic rupture calculations is obtained from the slip velocity distribution of a kinematic waveform inversion (KI) model by solving the elastodynamic equation with the kinematic slip as a boundary condition. Using the kinematic slip distribution and observed ground motion as constraints, a trial and error procedure was followed to define the stress parameterization. Preferred model describes the source in terms of stress with three asperities (located, respectively, at the deep, middle and shallow) and strong barriers between asperities. S-e is as high as 19 Mpa at barriers between the three asperities and Delta tau is maximum about 40 Mpa at the deepest asperity. This heterogeneity in stress distribution produces abrupt jumps in rupture velocity, exhibiting locally apparent rupture speed exceeding the P wave velocity at the borders between barriers and asperities, due to sharp changes of fault strength and stress drop at those areas. Overall, consistent with other studies, the rupture propagation is dominated by supershear speed toward the eastern asperities and at shallow surface. Simulated surface rupture at the eastern fault is consistent with other studies; nevertheless, the western shallower parts did not rupture during the simulation, suggesting that those regions may have already broken during the 1999 Kocaeli event, which occurred three months earlier. Ground motion simulation catches the major characteristics of the observed waveforms. Distribution of simulated peak ground velocity (PGV) in low frequency (0.1-0.5 Hz.) inside the study area reveals the propagation pattern on the field, with PGV reaching to 1.2 and 2.2 m/s in the NS and EW components, respectively.

We demonstrate that non-linear dynamic deformation exists throughout the crust and upper mantle of the Earth. Stress-aligned shear-wave splitting, seismic birefringence, is widely observed in the Earth’s upper crust, lower-crust, and uppermost ∼400 km of the mantle. Attributed to the effects of pervasive distributions of stress-aligned fluid-saturated microcracks in the crust (and controversially intergranular films of hydrated melt in the mantle), the degree splitting indicates that ‘microcracks’ are so closely spaced that they verge on failure in fracturing and earthquakes if there is any disturbance. Phenomena that verge on failure are critical systems with non-linear dynamics that impose a range of new properties on conventional sub-critical geophysics that we suggest is a New Geophysics. Consequently, shear-wave splitting provides directly interpretable information about the progress of non-linear dynamic deformation in the deep otherwise-inaccessible interior of the microcracked Earth. Possibly uniquely for non-linear dynamic phenomena, observation of shear-wave splitting allows the progress towards singularities to be monitored in deep in situ rock, so that earthquakes and volcanic eruptions can be predicted (we prefer stress-forecast). The response to other processes, such as hydraulic fracking, can be monitored, and in some cases calculated and effects predicted. Here, we review shear-wave splitting and demonstrate the prevalence of non-linear dynamic deformation of the New Geophysics in the crust and uppermost ∼400 km of the mantle.

In this study, the original seismograms of the 1935-Erdek–Marmara Island and 1963-Cinarcik Earthquakes, recorded at local and regional distances, were vectorized. The epicentral locations have been calculated using available readings from original records and also ISS and seismic station bulletins for 04.01.1935-14:41 and 16:20 Marmara Island–Erdek Earthquakes and 18.09.1963-16:58 Cinarcik Earthquake. The epicenter determinations show that the first event in 04.01.1935 was located at 40.72N–27.72E, while the second one occurred at 40.61N–27.43E, indicating that both were located near the Marmara Island. Another finding is that the 1963 event was located at 40.80N–29.18E, near the Princes’ Island fault. Furthermore, moment tensor inversion method was applied on these earthquakes by using original seismograms, which provided an opportunity to illuminate the seismotectonic features of Marmara Region based on the retrieved fault mechanism solutions. For the first time, the fault mechanisms for 04.01.1935-14:41 and 16:20 Earthquakes were determined using moment tensor inversion from the original seismic waveforms. Likewise, the result obtained for the fault mechanism of 1963 Cinarcik Earthquake showed normal fault mechanism with much shallower depth than estimated before. Our preferred solutions showed that the fault mechanisms for the three events are normal faults and coincide with the seismotectonic structure of the Marmara Region.

We investigated the crustal structure beneath the Marmara region and the surrounding area in the western part of the North Anatolian fault zone. These areas have high seismicity and are of critical significance to earthquake hazards. The study was based on travel-time tomography using local moderate and micro-earthquakes occurring in the study area recorded by the Multi-Disciplinary Earthquake Research in High Risk Regions of Turkey project and Kandilli Observatory and Earthquake Research Institute. We selected 2131 earthquakes and a total of 92,858 arrival times, consisting of 50,044 P-wave and 42,814 S-wave arrival times. We present detailed crustal structure down to 50 km depth beneath the Marmara region for P- and S-wave velocities using the LOTOS code based on iterative inversion. We used the distributions of the resulting seismic parameters (Vp, Vs) to pick out significant geodynamical features. The high-velocity anomalies correlate well with fracturing segments of the North Anatolian fault. High seismicity is mostly concentrated in these segments. In particular, low velocities were observed beneath the central Marmara Sea at 5 km depth.

Spain is a low-to-moderate seismicity area with relatively low seismic hazard. However, several strong shallow earthquakes have shaken the country causing casualties and extensive damage. Regional seismicity is monitored and surveyed by means of the Spanish National Seismic Network, maintenance and control of which are entrusted to the Instituto Geografico Nacional. This array currently comprises 120 seismic stations distributed throughout Spanish territory (mainland and islands). Basically, we are interested in checking the noise conditions, reliability, and seismic detection capability of the Spanish network by analyzing the background noise level affecting the array stations, errors in hypocentral location, and detection threshold, which provides knowledge about network performance. It also enables testing of the suitability of the velocity model used in the routine process of earthquake location. To perform this study we use a method that relies on P and S wave travel times, which are computed by simulation of seismic rays from virtual seismic sources placed at the nodes of a regular grid covering the study area. Given the characteristics of the seismicity of Spain, we drew maps for M L magnitudes 2.0, 2.5, and 3.0, at a focal depth of 10 km and a confidence level 95 %. The results relate to the number of stations involved in the hypocentral location process, how these stations are distributed spatially, and the uncertainties of focal data (errors in origin time, longitude, latitude, and depth). To assess the extent to which principal seismogenic areas are well monitored by the network, we estimated the average error in the location of a seismic source from the semiaxes of the ellipsoid of confidence by calculating the radius of the equivalent sphere. Finally, the detection threshold was determined as the magnitude of the smallest seismic event detected at least by four stations. The northwest of the peninsula, the Pyrenees, especially the westernmost segment, the Betic Cordillera, and Tenerife Island are the best-monitored zones. Origin time and focal depth are data that are far from being constrained by regional events. The two Iberian areas with moderate seismicity and the highest seismic hazard, the Pyrenees and Betic Cordillera, and the northwestern quadrant of the peninsula, are the areas wherein the focus of an earthquake is determined with an approximate error of 3 km. For M L 2.5 and M L 3.0 this error is common for almost the whole peninsula and the Canary Islands. In general, errors in epicenter latitude and longitude are small for near-surface earthquakes, increasing gradually as the depth increases, but remaining close to 5 km even at a depth of 60 km. The hypocentral depth seems to be well constrained to a depth of 40 km beneath the zones with the highest density of stations, with an error of less than 5 km. The M L magnitude detection threshold of the network is approximately 2.0 for most of Spain and still less, almost 1.0, for the western sector of the Pyrenean region and the Canary Islands.

The 2006 Mb = 5.3 Manyas-Kus Golu (Manyas) earthquake has been retrospectively "stress-forecasted" using variations in time-delays of seismic shear wave splitting to evaluate the time and magnitude at which stress-modified microcracking reaches fracture criticality within the stressed volume where strain is released. We processed micro earthquakes recorded by 29 TURDEP (Multi-Disciplinary Earthquake Research in High Risk Regions of Turkey) and 33 KOERI (Kandilli Observatory and Earthquake Research Institute) stations in the Marmara region by using the aspect-ratio cross-correlation and systematic analysis of crustal anisotropy methods. The aim of the analysis is to determine changes in delay-times, hence changes in stress, before and after the 2006 Manyas earthquake. We observed that clear decreases in delay times before the impending event, especially at the station GEMT are consistent with the anisotropic poro-elasticity (APE) model of fluid-rock deformation, but we could not observe similar changes at other stations surrounding the main event. The logarithms of the duration of the stress-accumulation are proportional (self-similar) to the magnitude of the impending event. Although time and magnitude of th 2005 Manyas earthquake could have been stress-forecasted, as has been recognized elsewhere, shear-wave splitting does not appear to provide direct information about the location of impending earthquakes.

We analyze the waveforms generated by the January 12, 2010 Haiti earthquake ( M w =7.0) for its source characteristics. A 60 to 25 km source model is retrieved by the Kikuchi and Kanamori finite source inversion technique that uses broadband teleseismic body wave records. The derived rupture model points out unilateral rupture propagation commenced at the eastern side of the fault plane where the major seismic moment release occurred. The rupture front propagated westward and terminated at a site where the largest aftershocks occurred. Our estimates yield a seismic moment of M o =8.17×10 19 N m released on a 60 km-long fault plane. A patch at the eastern side of the ruptured fault plane inferred as a region of maximum moment release. We also simulated the strong ground motion time histories recorded during the earthquake using the modified version of the stochastic modeling technique (FINSIM). In this technique, the finite-fault plane is subdivided into subfaults, and each element is assigned a stochastic ω 2 spectrum. In the modified version, a time axes for time differences between wave onsets at different seismic stations is added, and the stimulation and propagation of the compressional waves is considered. The optimal size of subfaults is selected as a function of the earthquake magnitude. The ground motion waveforms recorded at the nearest station to the epicenter (SDDR) are used in the comparisons. We tested two models: one with a fault plane size from 60 to 25 km, and a second model with a fault plane size of 35–25 km. A good agreement is found between time histories, response spectra of the simulated and the observed data using the model with a fault plane size of 60–25 km. In addition, peak ground acceleration (PGA) distribution obtained by modified version of FINSIM is compared with PGA distribution obtained by USGS ShakeMap for Port-au-Prince and circumferences.

Two recent catastrophic earthquakes that struck the Marmara Region on 17 August 1999 ( M w =7.4) and 12 November 1999 ( M w =7.2) caused major concern about future earthquake occurrences in Istanbul and the Marmara Region. As a result of the preparations for an expected earthquake may occur around Istanbul region, an earthquake early warning system has been established in 2002 with a simple and robust algorithm, based on the exceedance of specified thresholds of time domain amplitudes and the cumulative absolute velocity (CAV) levels (Erdik et al., 2003 [1] ). In order to improve the capability of Istanbul earthquake early warning system (IEEWS) for giving early warning of a damaging earthquake in the Marmara Region, we explored an alternative approach with the use of a period parameter ( τ c ) and a high-pass filtered vertical displacement amplitude parameter ( Pd ) from the initial 3 s of the P waveforms as proposed by Kanamori (2005) [2] and Wu and Kanamori (2005) [3,4] . The empirical relationships both between τ c and moment magnitude ( M w ), and between Pd and peak ground velocity (PGV) for the Marmara Region are presented. These relationships can be used to detect a damaging earthquake within seconds after the arrival of P waves, and can provide on-site warning in the Marmara Region.

Belbasi Seismic Station is composed of two seismic sub-arrays. One is a medium-period seismic array with a radius of about 45 km located in Ankara, and the second is a short-period seismic array with a radius of about 3 km located in Keskin. The distance between the two arrays is approximately 80 km. Both arrays consist of seven elements. Each array has a broadband seismometer located at the middle element of the circular array. Short-period vertical seismometers (Geotech 23900) are installed at depth 30 m from the surface while medium and broadband instruments (Geotech KS54000) are installed at depth 60 m from the surface. The purpose of this study is to analyze the short-period detection capability of the Keskin array using crustal events from earthquakes near Bala, in the central Anatolia region of Turkey (Figure 1). The epicentral distances of the Bala events to the Keskin array is about 50 km. Techniques for processing array data are based on the assumption that the seismic wave field propagates as a plane wave across the array, allowing a simple prediction of the time of arrival of a wave front at each station for a given azimuth of arrival and phase velocity of propagation. This is a good approximation for teleseismic events but is a restriction for near-receiver studies. Our study is limited to local events (Rost and Thomas 2002). For typical arrays, this means that the seismic phase is virtually unchanged as it propagates from element to element. In addition, arrays are designed with an element spacing that tries to preserve the correlation of the signal (signal coherency) and exploit a lack of correlation of noise at frequencies of interest so that simple time shifting and summation will cause the signal to add constructively and the decorrelated noise to add destructively, increasing …

The Aegean Sea is one of the more seismically active areas in the Euro-Mediterranean region. The seismic activity in the Aegean Sea is monitored by a number of local agencies that contribute their data to the International Seismological Centre (ISC). Consequently, the ISC Bulletin may serve as a reliable reference for assessing the capabilities of local agencies to monitor moderate and low magnitude earthquakes. We have compared bulletins of the Kandilli Observatory and Earthquake Research Institute (KOERI) and the ISC, for the period 1976–2003 that comprises the most complete data sets for both KOERI and ISC. The selected study area is the East Aegean Sea and West Turkey, bounded by latitude 35–41°N and by longitude 24–29°E. The total number of events known to occur in this area, during 1976–2003 is about 41,638. Seventy-two percent of those earthquakes were located by ISC and 75% were located by KOERI. As expected, epicentre location discrepancy between ISC and KOERI solutions are larger as we move away from the KOERI seismic network. Out of the 22,066 earthquakes located by both ISC and KOERI, only 4% show a difference of 50 km or more. About 140 earthquakes show a discrepancy of more than 100 km. Focal Depth determinations differ mainly in the subduction zone along the Hellenic arc. Less than 2% of the events differ in their focal depth by more than 25 km. Yet, the location solutions of about 30 events differ by more than 100 km. Almost a quarter of the events listed in the ISC Bulletin are missed by KOERI, most of them occurring off the coast of Turkey, in the East Aegean. Based on the frequency-magnitude distributions, the KOERI Bulletin is complete for earthquakes with duration magnitudes Md > 2.7 (both located and assigned magnitudes) where as the threshold magnitude for events with location and magnitude determinations by ISC is mb > 4.0. KOERI magnitudes seem to be poorly correlated with ISC magnitudes suggesting relatively high uncertainty in the magnitude determinations. It is apparent that KOERI, like other agencies in the region, will greatly benefit from a much improved regional cooperation.

We present a preliminary study of strong ground motion during the largest aftershock (Mw 5.8) of the 1999 Izmit earthquake (Mw 7.4), Turkey, at 11:55 on 13 September 1999. The peak ground acceleration observed near the epicentre of this aftershock was in agreement with that predicted by standard empirical prediction equations. Its spectral source parameters of the largest aftershock are also typical for a Mw 5.8 earthquake. At greater epicentral distances, there is an order-of-magnitude in scatter in peak ground acceleration values for this aftershock, which is attributed to site effects. The presence of thick layers of low-velocity sediments caused significant amplification of S-waves in the Avcilar district of Istanbul, at frequencies of ∼1 Hz, explaining the observed concentration of damage there as a result of the Izmit mainshock.

In this study, the focal mechanism solutions and spatial distributions of 100 intermediate-depth earthquakes are examined and discussed. These earthquakes occurred from 1985 to 1993 mostly in the upper and lower planes of the double seismic zone beneath the southeastern part of Hokkaido. The focal-mechanism solutions along with the spatial distribution of their epicenters as a function of depth and the minimum- and maximum-compressive stress directions confirm the following essential features; A double-planed deep seismic zone between the depths from 60 to 120 km has been clearly revealed in this region and the number of earthquakes located in the upper plane are less than those for the lower one. Low-angle thrust fault mechanism is dominant to a depth of about 55–60 km in the zone. At depths deeper than about 60 km focal mechanism solutions are mostly characterized by down-dip extension type or down-dip compression type in both lower and upper planes of the zone. Most of the earthquakes deeper than 60 km have dip-slip components and some of the solutions have significant strike-slip components, as well. Although the down-dip extensional-type events are dominant, seven events that are located on the lower plane are constrained as down-dip compression mechanism. The T axes of earthquake focal mechanisms on the lower plane show extension at about N40°E and N35°W, and the dip-angle between 25° and 70°, almost coincide with the dip of the subducting Pacific Plate in this region. We also investigate the statistical features of the stress directions of the earthquakes occurring both on the lower and upper plane after converting all the events onto the plane having the same strike and dip angle as the subducting lithosphere in the region. Seventy-two percent of the minimum compressive stress directions are oriented mainly in the NS or NNE- SSW directions (within 45° of the dip direction) at the plate surface of the lower plane and are almost parallel to the dip of the local slab in this region. The number of earthquakes located in the upper plane is less than that for the lower one. Those which occurred on the upper plane show various types of mechanism solutions. Weak systematic orientation is found in the direction distribution of stress in the upper plane.

We have simulated the waveforms of three aftershocks of the Izmit (17 August 1999) earthquake, with magnitudes greater than M 5.0, to determine the lithospheric structure of the Gulf of Izmit, Marmara region. Using the discrete wavenumber technique (Bouchon, 1981), different layered crustal models have been tested for the simulation of the waveforms, and the best crustal model was determined by a best-fit criterion between the observed and simulated seismograms. Our results indicate that the average thickness of the crust is 32 km and that Pn and S velocities are 8.0 and 4.60 km/sec, respectively, in the Gulf of Izmit, Marmara region. We also computed synthetic waveforms of the 21 April 2000 Denizli (Honaz) and the 9 July 1998 Izmir (Doganbey) earthquakes in the Aegean in order to compare the lithospheric structures of the Marmara and the Aegean regions. The Aegean region has an average crustal thickness of 33 km and Pn and S velocities of 7.85 and 4.53 km/sec, respectively. Although thicknesses of the crusts are comparable and suggest an approximately equal amount of E-W stretching in the Marmara and N-S stretching in the Aegean regions, a patchy midcrustal low-velocity zone exists in the Aegean. The upper-mantle Pn velocity variation between the Marmara and the Aegean regions is interpreted as the effect of a thinning continental lithosphere toward the active Aegean arc and the establishment of a consequent upper-mantle temperature gradient, increasing from the north to the south. Additionally, the Black Sea oceanic lithosphere that steeply dips southward beneath the Marmara region, as evidenced by the seismic tomographic results obtained by Gulen and Kuleli (1995), can contribute to the advective cooling of the upper mantle that causes relatively high Pn velocities in the Marmara region. Manuscript received 20 August 2000.

On 15 January, 1993, a large intermediate-depth earthquake with a magnitude of M=7.8, shook the eastern part of the island of Hokkaido, Japan, close to the northeastern Japan trench and to the Kuril trench; this earthquake is now referred to as the Kushiro-Oki earthquake. The main shock of the Kushiro-Oki earthquake showed a down-dip extension mechanism having horizontal and vertical nodal planes. The hypocenter was located at a depth of 107 km in the lower plane of the double seismic zone in the subducting Pacific plate. After the mainshock, more than 300 aftershocks were recorded by three seismograph networks. From these data we were able to determine the aftershock hypocenters and 63 focal mechanism solutions for the aftershocks. The aftershock region extended horizontally in a northerly direction from the lower plane towards the upper plane of the double seismic zone in the subducting plate; it did not, however, reach the upper plane. We estimated the maximum and minimum compressional stress directions along the deep seismic zone by converting the mechanism solutions from horizontal plane projections to an oblique plane parallel to the deep seismic zone. Thirty-eight mechanisms were found to have maximum and minimum compressional stress directions very similar to those of the mainshock, but 25 aftershock mechanisms had almost opposite directions to those of the mainshock. The hypocenters of these aftershocks were spatially mixed. This suggests that the stress state is strongly inhomogeneous in the aftershock region, and that horizontal movement occurs by the down-dip extensional stress which is stored in the region between two planes of the deep seismic zone. The remanent down-dip extensional stress was released as the consistent group of aftershocks. High aftershock activity may be attributed to the inhomogeneity of the material in the region. The previous four intermediate-depth earthquakes beneath Hokkaido Island as well as aftershock distributions of two of them have been examined for comparison with the Kushiro-Oki earthquake. The mainshocks of the four large intermediate-depth earthquakes are also located on the lower plane with a similar mechanism to that of the Kushiro-Oki earthquake. The aftershock regions of two of these earthquakes are also distributed horizontally. They indicate dominantly horizontal movement, with down-dip extension mechanisms at an intermediate depth in the subducting Pacific plate beneath Hokkaido Island.

Tsunami mitigation, preparedness and early warning initiatives have begun at the global scale only after the tragic event of Sumatra in 2004. Turkey, as a country with a history of devastating earthquakes, has been also affected by tsunamis in its past. In this paper we present the Tsunami Hazard in the Eastern Mediterranean and its connected seas (Aegean, Marmara and Black Sea) by providing detailed information on historically and instrumentally recorded significant tsunamigenic events surrounding Turkey, aiming to a better understanding of the Tsunami threat to the Turkish coasts. In addition to the review of the Tsunami hazard, we have studied a possible Tsunami source area between Rhodes and SW of Turkey using Tsunami numerical model NAMI DANCE-two nested domains. We have computed a maximum positive amplitude of 1.13 m and maximum negative amplitude of -0.5 m at the Tsunami source by this study. The distribution of maximum positive amplitudes of the water surface elevations in the selected Tsunami forecast area and time histories of water level fluctuations near selected locations (Marmaris, Dalaman, Fethiye and Kas towns) indicate that the maximum positive amplitude near the coast in the selected forecast area exceeds 3.5 m. The arrival time of maximum wave to Marmaris, Dalaman, is 10 min, while that of Fethiye and Kas towns is 15-20 min. The maximum positive amplitudes near the shallow region of around 10 m depth are 3 m (Marmaris), 1 m (Dalaman), 2 m (Fethiye) and 1 m (Kas). Maximum positive amplitudes of water elevations in the duration of 4 h simulation of the Santorini-Minoan Tsunami in around 1600 BC in the Aegean Sea are also calculated based on a simulation performed using 900 m grid resolution of Aegean sea bathymetry with a 300 m collapse of 10 km diameter of Thera (Santorini) caldera. We have also presented the results of the Tsunami modeling and simulation for Marmara Sea obtained from a previous study. Last part of this paper provides information on the establishment of a Tsunami Warning Center by KOERI, which is expected to act also as a regional center under the UNESCO Intergovernmental Oceanographic Commission - Intergovernmental Coordination Group for the Tsunami Early Warning and Mitigation System in the North-Eastern Atlantic, the Mediterranean and Connected Seas (ICG/NEAMTWS) initiative, emphasizing on the challenges together with the future work needed to be accomplished. (C) 2010 Elsevier Ltd. All rights reserved.