Earthquake Research Institute Research Articles

Scientists Examine Challenges and Lessons From Japan's Earthquake and Tsunami

A week after the magnitude 9.0 great Tohoku earthquake and the resulting tragic and damaging tsunami of 11 March struck Japan, the ramifications continued, with a series of major aftershocks (as Eos went to press, there had been about 4 dozen with magnitudes greater than 6); the grim search for missing people—the death toll was expected to approximate 10,000; the urgent assistance needed for the more than 400,000 homeless and the 1 million people without water; and the frantic efforts to avert an environmental catastrophe at Japan's damaged Fukushima Daiichi Nuclear Power Station, about 225 kilometers northeast of Tokyo, where radiation was leaking. The earthquake offshore of Honshu in northeastern Japan (see Figure 1) was a plate boundary rupture along the Japan Trench subduction zone, with the source area of the earthquake estimated at 400–500 kilometers long with a maximum slip of 20 meters, determined through various means including Global Positioning System (GPS) and seismographic data, according to Kenji Satake, professor at the Earthquake Research Institute of the University of Tokyo. In some places the tsunami may have topped 7 meters—the maximum instrumental measurement at many coastal tide gauges—and some parts of the coastline may have been inundated more than 5 kilometers inland, Satake indicated. The International Tsunami Information Center (ITIC) noted that eyewitnesses reported that the highest tsunami waves were 13 meters high. Satake also noted that continuous GPS stations indicate that the coast near Sendai—which is 130 kilometers west of the earthquake and is the largest city in the Tohoku region of Honshu—moved more than 4 meters horizontally and subsided about 0.8 meter.

Brief communication "Fast-track earthquake risk assessment for selected urban areas in Turkey"

Abstract. This study is presented as a contribution to earthquake disaster mitigation studies for selected cities in Turkey. The risk evaluations must be based on earthquake hazard analysis and city information. To estimate the ground motion level, data for earthquakes with a magnitude greater than 4.5 and an epicenter location within a 100-km radius of each city were used for the period from 1900 to 2006, as recorded at the Kandilli Observatory and Earthquake Research Institute. Probabilistic seismic hazard analysis for each city was carried out using Poisson probabilistic approaches. Ground motion level was estimated as the probability of a given degree of acceleration with a 10% exceedence rate during a 50-year time period for each city. The risk level of each city was evaluated using the number of houses, the per-capita income of city residents, population, and ground motion levels. The maximum risk level obtained for the cities was taken as a reference value for relative risk assessment, and other risk values were estimated relative to the maximum risk level. When the selected cities were classified according to their relative risk levels, the five most risky cities were found to be, in descending order of risk, Istanbul, Izmir, Ankara, Bursa, and Kocaeli.

Japan Earthquake—When the Big One Hit [Associate Editor's View

Japan is among the most earthquake-prone countries in the world. It lies across four slabs of rock, known as tectonic plates, that cause earthquakes when they rub against each other. Experts believe that Tokyo, which sits on a major fault line, has been overdue for a strong earthquake for decades. The problem, according to Prof. Keiji Doi from Tokyo University's Earthquake Research Institute, is there's no way of knowing when it will happen.

Radon Monitoring as the Earthquake Precursor in Fault Line in Western Turkey

Variations in radon concentrations near the earth's surface can provide important information about seismic activities. Continuous monitoring of radon concentrations is one of the important steps in predicting earthquake mechanisms. This study monitored the radon concentration of an active tectonic zone in western Turkey. Four sampling stations in the seismic area, of the Tuzla fault line, were selected for radon monitoring. The online radon monitoring system was placed at Cumalý station. Concurrently, the radon concentrations in the soil gas were continuously measured using LR-115 nuclear track detectors and an online radon measurement system. Data obtained from Bogazici University Kandilli Observatory and Earthquake research Institute was incorporated in the analysis to correlate with the collected radon concentration. The radon concentrations were measured using solid-state nuclear track films (LR-115) in the soils of thermal water fields, which varied from 40 track cm -2 week -1 to 1580 track cm -2 week -1 .

Investigation of microseismic activity sources in Konya and its vicinity, central Turkey

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

Discrimination of quarry blasts and earthquakes in the vicinity of Istanbul using soft computing techniques

The purpose of this article is to demonstrate the use of feedforward neural networks (FFNNs), adaptive neural fuzzy inference systems (ANFIS), and probabilistic neural networks (PNNs) to discriminate between earthquakes and quarry blasts in Istanbul and vicinity (the Marmara region). The tectonically active Marmara region is affected by the Thrace-Eskişehir fault zone and especially the North Anatolian fault zone (NAFZ). Local MARNET stations, which were established in 1976 and are operated by the Kandilli Observatory and Earthquake Research Institute (KOERI), record not only earthquakes that occur in the region, but also quarry blasts. There are a few quarry-blasting areas in the Gaziosmanpaşa, Çatalca, Ömerli, and Hereke regions. Analytical methods were applied to a set of 175 seismic events (2001–2004) recorded by the stations of the local seismic network (ISK, HRT, and CTT stations) operated by the KOERI National Earthquake Monitoring Center (NEMC). Out of a total of 175 records, 148 are related to quarry blasts and 27 to earthquakes. The data sets were divided into training and testing sets for each region. In all the models developed, the input vectors consist of the peak amplitude ratio (S/P ratio) and the complexity value, and the output is a determination of either earthquake or quarry blast. The success of the developed models on regional test data varies between 97.67% and 100%.

RECENT EFFORTS IN ISTANBUL TO PROTECT MUSEUM COLLECTIONS FROM DAMAGE DUE TO EARTHQUAKES

The city of Istanbul is located on two continents and has thousands of years of rich history, but it has also been affected by major earthquakes throughout this period and another significant seismic event is expected in the near future. Istanbul hosts numerous museums that make available a wide range of collections that represent universal heritage and most of these museums are located in historical buildings. Through the years earthquakes have caused significant damage to historical structures in Istanbul and an important issue is the protection of these buildings and collections now and in the future. Bogazici University, Kandilli Observatory and Earthquake Research Institute and the Museum Studies Graduate Program of Yildiz Technical University are leading institutions with respect to research and initiatives aimed at protecting museum collections from earthquake damage in Turkey.This contribution discusses improvements in the seismic protection of collections as well as recent efforts focusing on the development of a distance learning educational package being developed in Turkey that addresses seismic risk mitigation.

The Self-organizing Seismic Early Warning Information Network (SOSEWIN)

Rapid urbanization, the interconnection of economies and increasing dependence on technology makes modern society ever more vulnerable to natural disasters. This is particularly true when considering the growth of so-called mega cities (defined by the United Nations as metropolitan areas with populations exceeding 10 million), the majority of which are in the developing world. This has led to the recognition of the importance of early warning systems as one means of mitigating the potential human and economic losses resulting from natural disasters ( e.g. , International Strategy for Disaster Reduction 2005; United Nations 2006). Considering earthquakes, many areas of major urbanization ( e.g. , Tokyo, Istanbul, Naples, Mexico City) are exposed to significant seismic hazard. Currently, several parts of the world have some form of earthquake early warning system (EEWS) either in operation or under development ( e.g. , Taiwan: Wu and Teng 2002; Japan: Horiuchi et al. 2005; California: Wurman et al. 2007; Istanbul: Erdik et al. 2003; Bucharest: Ionescu et al. 2007; Mexico City: Espinosa-Aranda et al. 1995). However, these systems usually involve the use of a relatively low number of sensors (from several to tens of units), a fact largely dictated by the high cost of such instrumentation. In addition, these systems must usually communicate their data to centralized processing and archiving facilities. An example of a standard centralized EEWS is the Istanbul Earthquake Rapid Response and Early Warning System (IERREWS; Erdik et al. 2003) operated by Kandilli Observatory and Earthquake Research Institute (KOERI) of Bogazici University (Figure 1A). This system is made up of 10 strong-motion stations that are installed as close as possible to the fault zone of the north Anatolian fault, which runs through the Marmara Sea to the south of Istanbul. In the IERREWS, a centralized philosophy of early …

Space-based technologies and high performance computing in support of environmental sustainability in developing countries

Inspired by recent service on the User Working Group for NASA’s Socio-Economic Data Applications Center (SEDAC), the Science Review Panel for the Arctic Region Supercomputer Center, the Technology Advisory Committee for South Africa’s Center for High Performance Computing and participation in the NATO Pilot Study on Clean Products and Processes over the past four years, our distributed interdisciplinary research collaborators intensified our efforts to address some of the fundamental issues with respect to societal sustainability. We particularly focused on highly vulnerable communities, at risk for an array of immediate and long-term biogenic and anthropogenic disasters. Specifically, we sought to address the question: ‘‘How should state-of-the-science computational capabilities and earth observing satellites be optimally placed in the service of environmental sustainability and sustainable development?’’ In the on-going process of examining this issue, it has been encouraging to observe the technological progress that has recently occurred within Latin America, Asia and Africa. CONAE http://www.conae.gov.ar/eng/aplicaciones/ salud_new.html, the Argentine Space Agency’s SAC-C satellite has been operational since 2000 and its successor, Aquarius (SAC-D) will be launched in 2010; while SABIA (SAC-E), the Argentine-Brazilian Satellite for Information on Food, Water and the Environment, ALSAT-2 (SAC-F) and SAOCOM 1-A, with microwave radar and a thermal infrared camera, are each currently under production. Brazil’s other collaboration with China, the ChineseBrazilian Earth Resources Satellite (CBERS) has been generously offered without licensure fees to developing countries. China, as well, freely offers its Fung Yun 1D MVISR globally to receiving stations. Robust earth observing satellite launch schedules are apparent in China, India, Japan, Korea, Taiwan and Thailand. African engagement in satellite remote sensing has been actively promoted by the African Association for Remote Sensing of Environment (AARSE) and by the 2009 IEEE International Geo-science & Remote Sensing Symposium (IGARSS) held in Cape Town, South Africa. As a follow-on to the NATO Committee on the Challenges to Modern Society’s Pilot Study on Clean Products & Processes, the NATO Science for Peace Program has awarded funding to establish the Kamal Ewida Earth Observatory http://www.itap.purdue.edu/pto/NATO_KEEO/ index_en.html, which will include real-time satellite ground stations in Egypt at Cairo University and Al Azhar University, primarily for early warning and mitigation of disasters, including storms, flooding and epidemics, through identifying and monitoring infectious disease vector habitat, as well as for facilitating natural resource management. This initiative is in collaboration with the Kandilli Observatory and Earthquake Research Institute at Bogazici University in Istanbul, Turkey and with the Purdue Terrestrial Observatory at Purdue University’s Rosen Center for Advanced Computing in West Lafayette, Indiana, USA. Analysis of the real-time satellite data will benefit from a recently installed IBM Blue Gene L Supercomputer at Egypt’s National Authority for Remote Sensing & Space Sciences (NARSS), which has the capability to produce data products in near-real-time, as input to decision support for time-critical events. The other civilian supercomputer facility on the African continent is at South G. L. Rochon (&) Purdue Terrestrial Observatory (PTO), Information Technology at Purdue (ITaP), Rosen Center for Advanced Computing (RCAC), Purdue University, 203 Martin Jischke Drive, Mann Hall 160, West Lafayette, IN 47907, USA e-mail: rochon@purdue.edu

GRiD MT (grid-based real-time determination of moment tensors) monitoring the long-period seismic wavefield

We have developed and implemented a new grid-based earthquake analysis system that continuously monitors long-period seismic wavefield of 20–50 s recorded by broadband seismometers. The new analysis system automatically and simultaneously determines the origin time, location and seismic moment tensor of seismic events within 3 min of their occurrence. This system has been in operation since 2003 at the Earthquake Research Institute ( http://wwweic.eri.u-tokyo.ac.jp/GRiD MT/), and the locations and origin times are usually obtained within 3 s and 20 km away from the earthquake catalog values determined by the Japan Meteorological Agency (JMA). In addition, moment tensor solutions are comparable to the network solutions manually obtained. This new system should enable us to monitor long-period seismic wavefield continuously further to help identifying long-period (or low-frequency) events which are undetectable by the conventional monitoring of short-period seismic wavefields.

DAMAGE ARTICLES APPEARED ON LOCAL NEWSPAPERS IN HOKKAIDO

Continuing to the previous paper, supplemental data concerning to the Off Nemuro Earthquake of March 22, 1894 are surveyed utilizing the scrapbooks of newspaper articles on earthquake disasters archived in Earthquake Research Institute, University of Tokyo. Recently these archived data are opened on the Web site of Headquarters of Earthquake Research Promotion, Japan. These articles are downloaded and arranged in time series and listed. More casualties and damage in rural area are found and tsunami disasters accompanied floating ices in various places are also revealed.

Accurate relocation of İzmit earthquake (Mw = 7.4, 1999) aftershocks in Çınarcık Basin using double difference method

We relocated part of the aftershock activity in Çınarcık Basin and surrounding areas that are associated with the 1999 İzmit earthquake Mw 7.4. Double difference relocation algorithm is used to relocate the aftershocks. The data set was obtained from a temporary seismic network deployed 10 days after the main shock by cooperation between Boğaziçi University Kandilli Observatory and Earthquake Research Institute, LGIT (Grenoble), and IPGP (Paris). For a better station coverage, additional data set was obtained from a network operated by TUBITAK Marmara Research Center. Differential travel times were calculated using both arrival time readings and waveform cross correlation method. We relocated 1145 of the aftershocks and interpreted the results with emphasis on the Yalova and Tuzla cluster located within the Marmara Sea. The results show better focused seismicity patterns for the Yalova cluster, providing clear evidence for the proposed models. We present a revised location of the 1963 Çınarcık earthquake which took place in area of Yalova cluster. Finally we propose that the activity of Tuzla cluster represents a parallel subsidiary fault of the Main Marmara Fault.

Comparison of hypocentre parameters of earthquakes in the Aegean region

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.

ML Scale in Northwestern Turkey from 1999 Izmit Aftershocks: Updates

We present an update of the local magnitude scale previously calibrated for northwestern Turkey by Baumbach et al. (2003). The path coverage in the westernmost part of the analyzed area has been increased, as well as the number of amplitudes for distance greater than 110 km. Furthermore, a set of recordings from accelerometric stations operated by the Kandilli Observatory and Earthquake Research Institute (koeri) has been merged with the recordings by the Sapanca-Bolu and German Task Force seismological networks. In all, 4047 recordings from 528 earthquakes recorded by 31 seismometers and 23 accelerometers are considered to calibrate the local magnitude scale over a hypocentral distance range from 10 to 190 km. By analyzing the unit covariance matrix and the resolution matrix, we show how the source-to-station geometries of the seismic and strong-motion networks affect the uncertainties of the computed station corrections, attenuation coefficients, and magnitudes. The assumptions made concerning the reference station correction, and the change in the amplification for the Wood–Anderson torsion seismograph from 2800 to 2080 (Uhrhammer and Collins, 1990) introduced an offset of about 0.34 in the magnitudes with respect to Baumbach et al. (2003), with the updated local magnitude scale ranges from 0.50 to 5.91. The distribution of the residuals with distance confirms that the extension of both the magnitude and distance ranges and the improved path coverage have preserved the high quality that characterized the data set analyzed by Baumbach et al. (2003).

Development of MTSAT data processing, visualization and distribution system on WWW

This research focuses on a network based data distribution and visualization system of Multi-functional Tranport SATellite (MTSAT) . Institute of Industrial Science (IIS) and Institute of Earthquake Research Institute (ERI) both at University of Tokyo have been receiving, processing, archiving and dis-tributing of MTSAT imagery with a direct receiving of High Rate Information Transmit (HRIT) since October 2006. A software package, mtsatgeo, is developed including radiometric calibration, geometric cor-rection and spatial subset, and they are available on a web-based data distribution and processing service accessed at http: //webgms.iis.u-tokyo.ac.jp/

Observation and analysis of low-frequency crustal earthquakes in Lake Van and its vicinity, eastern Turkey

Lake Van is located in very intensely deformed tectonic settings in the eastern Turkey. The surrounding area of Lake Van has major tectonic structures; NE and NW trending active conjugate strike-slip faults, pull-apart basins along these faults, E-W trending active thrust faults, folds, compressional ramp basins, N-S trending folds, NE-SW aligned continental collision-related volcanoes and N-S trending tensional cracks functioned as magma conduits. Since the area is tectonically very active, the earthquake activity within the basin and the surrounding area of Lake Van is very high. In this study, we have analysed the records of VANB broadband station of Kandilli Observatory and Earthquake Research Institute's network for the seismic events (2000–2004) that occurred in the basin and in the vicinity of Lake Van. Based on the spectral analysis of earthquake data, we have mainly observed three types of seismic events; hybrid event, long period event and tremor. We have suggested that the observed hybrid, long period and tremor type of seismic events that occurred in the study area are related to the upward moving materials and stress loading in the mid and lower crust based on the geophysical data.

Radon concentrations in thermal waters related to seismic events along faults in the Denizli Basin, Western Turkey

The aim of this study is to investigate the relationship between the earthquakes and radon concentrations in thermal waters along faults in the Denizli Basin, an area in Turkey known for its high seismic activity and thermal waters. This area was chosen because it exhibits active crustal movements combined with seismicity and there are numerous outflow thermal waters and gas outputs. In addition, this region has the type of tectonic activity where graben groups and faults take place. Measurements of radon levels and of some chemical and physical characteristics of thermal waters were made at seven sampling stations in the region. Radon concentrations were measured by a ZnS(Ag) scintillation counter in a collector chamber. The activity levels varied between 0.67 and 25.90 kBq m - 3 during the period of May–December 2000. In the evaluation of the results, the seismic data reported by Bogaziçi University Kandilli Observatory and Earthquake Research Institute, Seismological Laboratory were used. The increases observed in radon concentration at two stations were probably related to the earthquakes that took place in the region during the study period.

Effects of Irregular Structure of the Mississippi Embayment on Ground-Motion Amplification

The objective of this study is to evaluate effects of the presently available 3D velocity model of the Mississippi embayment structure on the amplification of seismic waves by using simulated finite-difference seismograms. Effects of both 2D and 3D embayment basement structures were considered. The 3D model included information of the near-surface velocities that were derived from the existing 1D velocity models. The 2D crustal model was taken from Catchings (1999), which extended from Saint Louis, Missouri, to Memphis, Tennessee. Finite-difference seismograms were simulated for point sources embedded at both ends of the 2D structure. These seismograms were examined to distinguish features like peak amplitude amplifications and duration of seismograms when the seismic waves propagated from the Mississippi Embayment toward the Illinois basin and vice versa. To establish a working 3D structure model of the embayment, we compiled geologic information of the region on material properties of the shallow structure and used the 3D model developed at the Center of Earthquake Research Institute (ceri), Memphis, as the starting model. The 3D model was used to generate finite-difference seismograms along several profiles for a M w 7.2 scenario earthquake occurring on the New Madrid fault zone. An equivalent 1D model, which included the basin materials, was also used to compare the 3D versus equivalent 1D ground motions simulated using the finite-difference method. To establish the amplification factors due to the surface sediments in the 3D model, finite-difference seismograms were also computed for a 1D hard-rock reference model. These 1D and 3D responses of the Mississippi embayment were used for estimating ground-motion amplification at sites where the depth to the basement is deeper than 500 m. Our investigation suggests that the deep structure of the Mississippi Embayment has little impact on long-period ground- motion amplitudes ( T ≥ 2 sec) for large earthquakes that rupture in the central part of the basin. This supports the hypothesis that for engineering purposes ground motions simulated based on the equivalent 1D crustal model are adequate for representing ground motions from future large earthquakes ( M w > 7) occurring in the New Madrid seismic zone.

Relocation of Early and Late Aftershocks of the 2001 Bhuj Earthquake Using Joint Hypocentral Determination (JHD) Technique: Implication toward the Continued Aftershock Activity for more than Four Years

We employed layered model joint hypocentral determination (JHD) with station corrections to improve location identification for the 26 January, 2001 Mw 7.7 Bhuj early and late aftershock sequence. We relocated 999 early aftershocks using the data from a close combined network (National Geophysical Research Institute, India and Center for Earthquake Research Institute, USA) of 8–18 digital seismographs during 12–28 February, 2001. Additionally, 350 late aftershocks were also relocated using the data from 4–10 digital seismographs/accelerographs during August 2002 to December 2004. These precisely relocated aftershocks (error in the epicentral location<30 meter, error in the focal depth estimation < 50 meter) delineate an east-west trending blind thrust (North Wagad Fault, NWF) dipping (~ 45°) southward, about 25 km north of Kachchh main land fault (KMF), as the causative fault for the 2001 Bhuj earthquake. The aftershock zone is confined to a 60-km long and 40-km wide region lying between the KMF to the south and NWF to the north, extending from 2 to 45 km depth. Estimated focal depths suggest that the aftershock zone became deeper with the passage of time. The P- and S-wave station corrections determined from the JHD technique indicate that the larger values (both +ve and -ve) characterize the central aftershock zone, which is surrounded by the zones of smaller values. The station corrections vary from −0.9 to +1.1 sec for the P waves and from −0.7 to +1.4 sec for the S waves. The b-value and p-value of the whole aftershock (2001–2004) sequences of Mw ≥ 3 are estimated to be 0.77 ± 0.02 and 0.99 ± 0.02, respectively. The p-value indicates a smaller value than the global median of 1.1, suggesting a relatively slow decay of aftershocks, whereas, the relatively lower b-value (less than the average b-value of 1.0 for stable continental region earthquakes of India) suggests a relatively higher probability for larger earthquakes in Kachchh in comparison to other stable continental regions of the Indian Peninsula. Further, based on the b-value, mainshock magnitude and maximum aftershock magnitude, the Bhuj aftershock sequence is categorized as the Mogi's type II sequence, indicating the region to be of intermediate level of stresses and heterogeneous rocks. It is inferred that the decrease in p-value and increase in aftershock zone, both spatially as well as depth over the passage of time, suggests that the decay of aftershocks perhaps could be controlled by visco-elastic creep in the lower crust.

Crustal structure and local seismicity in western Anatolia

SUMMARY Western Anatolia is one of the most seismically active continental regions in the world and much of it has been undergoing NS-directed extensional deformation since Early Miocene time. In a cooperative study, seismologists from Saint Louis University, USA and Dokuz Eylul University, Turkey, deployed five broad-band and 45 short-period seismic stations in western Anatolia between 2002 November and 2003 October. The present paper uses data collected by this network and the data from five permanent stations operated by the Kandilli Observatory and Earthquake Research Institute to map the hypocentral distribution of local earthquakes and to determine crustal structure of western Anatolia. We obtained a 1-D P-wave crustal velocity model using a generalized scheme for simultaneously obtaining earthquake locations and a crustal velocity model. Our velocity model is characterized by crustal velocities that are significantly lower than average continental values. The low velocities may be associated with high crustal temperatures, a high degree of fracture, or the presence of fluids at high pore pressure in the crust. We located 725 local earthquakes and classified them in three categories. We found that the level of seismic activity in western Anatolia is higher than previously reported. Station delays resulting from the inversion process correlate with near-surface geology and the thickness of sediments throughout the region. The hypocentral distribution of the events indicates that peak seismicity for the region occurs at depths of about 10 km.