Earthquake Research Institute Research Articles

Bayesian estimation of source parameters and associated Coulomb failure stress changes for the 2005 Fukuoka (Japan) Earthquake

We thank Shin’ichi Miyazaki (Kyoto Univ.) for discussions and the Earthquake Research Institute (Univ. Tokyo) for hosting SJ during the early part of this work. Comments from Yukitoshi Fukahata (Kyoto Univ.) and an anonymous reviewer improved the manuscript. We thank Chiheb Hammouda (KAUST) for fruitful discussions. The ENVISAT data were provided by the European Space Agency through category-1 project 3639. Generic Mapping Tools (GMT) were used to make Figure 1. This research was supported by King Abdullah University of Science and Technology (KAUST).

Source mechanisms and faulting analysis of the aftershocks in the Lake Erçek area (Eastern Anatolia, Turkey) during the 2011 Van event (Mw 7.1): Implications for the regional stress field and ongoing deformation processes

In this study, we analysed the source mechanisms and faulting pattern of the aftershocks in the Lake Erçek area, Eastern Anatolia, during the 2011 Van event (Mw 7.1). The fault plane solutions of the aftershocks were used to derive a stress tensor acting around Lake Erçek. The estimated seismological parameters (focal mechanism solutions, stress tensor, and fault focal analyses) were integrated with field surveys and high resolution seismic reflection data so as to better understand the main faulting patterns and deformational features which are the causatives of the observed geomorphological features within and around Lake Erçek. The focal parameters of the 56 aftershocks with magnitude range 3.5≤Mw≤5.5 were obtained using the regional broadband seismic data from the network of Kandilli Observatory and Earthquake Research Institute (KOERI) through the Centroid Moment Tensor (CMT) inversion of locally observed broadband-waves. The implications for the lateral variation of the stress field in the lake area were based on information derived from integration of seismicity and stress tensor inversion results. The major outcomes of our analyses were as follows: (a) The maximum principal stress axis is close to horizontal and aligned in NNW-SSE direction, the minimum compressional stress axis is close to vertical and aligned in an ENE-WSW direction, the intermediate stress axis is close to horizontal and is parallel to the strike of the ruptured fault plane, while the stress ratio is (R=0.6); (b) the lake basin is mostly deformed by dip-slip faults (dips≥45–60°) in and along its margins where the various folds, basement highs with eroded surfaces and several low-angle normal faults are evident; (c) the majority of the aftershocks have reverse-thrust mechanism with some strike-slip components in the Lake Erçek area (N- and S-margins). Strike-slip and normal faulting events are also evident (E- and W-margins, respectively); (d) the normal and reverse mechanisms with some strike-slip component are mostly confined in the upper crust (0–15km), compatible with NS-striking normal and WE-striking reverse faults in the marginal sections of the lake; (e) the WE-striking reverse faulting in the N- and S-margins seems to have the seismic potential to generate destructive earthquakes in the lake area; (f) the tectonic implications of the regional stress field and ongoing deformation processes in the lake are defined and supported by field observations and seismic reflection data. The result of these analyses reveals N-S compression/W-E extension in the lake and also the collisional/compressional regime taking place in a region of Lakes Van and Erçek.

“Urban Resilience” for Mega Earthquake Disasters Part 2

Based on the lessons from the 2011 Great East Japan Earthquake Disaster, the Ministry of Education, Culture, Sports, Science and Technology has launched “Special Project for Reducing Vulnerability for Urban Mega Earthquake Disasters (2012–2016)” with the aim of reducing the damages caused by the urban earthquake disasters such as the projected earthquake that directly hits Tokyo area and the Tokai, Tonankai and Nankai Earthquakes as much as possible. This project is divided into the following three subprojects: namely, 1) “Research and Study on Evaluation of Risk and Hazard of Earthquake that Directly Hits Tokyo Area” represented by Professor Naoshi Hirata, Earthquake Research Institute, the University of Tokyo; 2) “Research and Study on Maintenance and Recovery of Functionality in Urban Infrastructures” represented by Professor Masayoshi Nakashima, Disaster Prevention Research Institute, Kyoto University; and 3) “Research and Study on Measures to Improve Urban Resilience to Earthquake Disaster” represented by Dr. Haruo Hayashi, President of the National Research Institute for Earth Science and Disaster Resilience. This special issue focuses on the findings of the subproject 3). The subproject 3) aims to develop the information communication system for supporting efficient management of emergency responses and restoration efforts and promotion of the capabilities for solution of the problems in terms of disaster, i.e. disaster management literacy, to contribute to high resilience to disaster in our society.

Crustal S-wave structure around the Lake Van region (eastern Turkey) from interstation Rayleigh wave phase velocity analyses

This study focuses on the average crustal and the upper mantle structure throughout the Lake Van region of eastern Turkey. The study aimed to investigate the structure with the fundamental mode interstation Rayleigh wave phase velocities from the local and the regional earthquakes recorded by Kandilli Observatory and Earthquake Research Institute stations. Considering back azimuth differences of each source and station path, six different broadband station pairs and 27 earthquakes were selected to determine the 1-D shear-wave velocity structures throughout the region by using an interstation method (slant stacking technique). The linearized least squares algorithm was used to obtain the 1-D shear-velocity model that best fit the observed phase velocity dispersion curve. The normalized statistical resolution matrix was calculated to measure the reliability of the solution. Inversion results revealed that the solution quality of the upper crust is weak due to the high resolution lengths. The average shear-wave velocities in the lower crust scale down to approximately 3.5 km/s. It was inferred that this low-velocity zone shown in the lower crust may be associated with widespread volcanism. Final 2-D S-wave velocity models obtained from the inversion revealed that the crust-mantle boundary is ~42 km, and shear velocities vary from 3.6 to 4.2 km/s. Furthermore, the upper mantle (~45-70 km) velocities are slower than globally suggested models (e.g., IASP91), and this is possibly related to shallow hot asthenospheric material.

Regional Moment Tensor Inversion for Earthquakes in Turkey and Its Surroundings: 2008–2015

ABSTRACT Turkey and its surrounding regions are tectonically active and have high‐seismicity rates. The seismicity in the region is observed by the national networks of the Kandilli Observatory and Earthquake Research Institute (KOERI) and the Disaster and Emergency Management Presidency Earthquake Department (AFAD). The quality and quantity of seismic stations improved significantly after the 17 August 1999 M w 7.4 Izmit earthquake. In the meantime, a number of focal mechanism catalogs were produced, covering different time periods. However, a homogeneous long‐term catalog of moment tensor (MT) solutions with increased data amount and quality was not available for the region. In this article, we perform a systematic MT inversion of 133 M ≥4.5 earthquakes within Turkey between 2008 and 2015, using the dense seismic networks of KOERI and AFAD. The use of combined networks and site‐specific velocity models for the computation of MT inversion results in high‐quality solutions of focal mechanisms. This homogeneous focal mechanism catalog provides important new information on the seismotectonics in this region.

Investigating P- and S-wave velocity structure beneath the Marmara region (Turkey) and the surrounding area from local earthquake tomography

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.

A database for fatalities and damages due to the earthquakes in Turkey (1900–2014)

Considering the possibility of the reoccurrence of the earthquakes in which loss of life and property have accrued, the possibility of future losses can be minimized. In Turkey, although the information about the fatalities and damaged buildings might be contrived in the resources, those have limited information and contain substantial differences. Moreover, that information might not be presented in a common database. Some information presented by Turkey Prime Ministry Disaster & Emergency Management Authority, Kandilli Observatory and Earthquake Research Institute and United States Geological Survey is inconsistent not only in the number of earthquakes, fatalities, damaged buildings, the magnitude and intensity of earthquakes, but also at the date of the same earthquake. In this study, first, the resources providing the data regarding the earthquakes causing fatalities and damage between 1900 and 2014 in Turkey have been analyzed. Then, through examining all the databases, literature and available historical documents, a single updated list of the earthquakes that shows the fatalities and damages between 1900 and 2014 in Turkey has been prepared. Finally, in light of the data rearranged, the statistical facts about the losses in the historical earthquakes are presented.

A Poisson method application to the assessment of the earthquake hazard in the North Anatolian Fault Zone, Turkey

North Anatolian Fault (NAF) is one from the most important strike-slip fault zones in the world and located among regions in the highest seismic activity. The NAFZ observed very large earthquakes from the past to present. The aim of this study; the important parameters of Gutenberg-Richter relationship ( a and b values) estimated and this parameters taking into account, earthquakes were examined in the between years 1900-2015 for 10 different seismic source regions in the NAFZ. After that estimated occurrence probabilities and return periods of occurring earthquakes in fault zone in the next years, and is being assessed with Poisson method the earthquake hazard of the NAFZ. The 10 different seismic source regions are determined the relationships between the cumulative number-magnitude which estimated a and b parameters with the equation of LogN=a-bM in the Gutenberg-Richter. A homogenous earthquake catalog for M S magnitude which is equal or larger than 4.0 is used for the time period between 1900 and 2015. The database of catalog used in the study has been created from International Seismological Center (ISC) and Bogazici University Kandilli observation and earthquake research institute (KOERI). The earthquake data were obtained until from 1900 to 1974 from KOERI and ISC until from 1974 to 2015 from KOERI. The probabilities of the earthquake occurring are estimated for the next 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100 years in the 10 different seismic source regions. The highest earthquake occur probabilities in 10 different seismic source regions in the next years estimated that the region Tokat-Erzincan (Region 9) 99% with an earthquake occur probability for magnitude 6.5 which the return period 24.7 year, 92% with an earthquake occur probability for magnitude 7 which the return period 39.1 year, 80% with an earthquake occur probability for magnitude 7.5 which the return period 62.1 year, 64% with an earthquake occur probability for magnitude 8 which the return period 98.5 year. For the Marmara Region (Region 2) in the next 100 year estimated that 89% with an earthquake occur probability for magnitude 6 which the return period 44.9 year, 45% with an earthquake occur probability for magnitude 6.5 which the return period 87 year, 45% with an earthquake occur probability for magnitude 7 which the return period 168.6 year.

Crustal S-wave structure beneath Eastern Black Sea Region revealed by Rayleigh-wave group velocities

In this study, the crustal S-wave structure beneath the Eastern Black Sea Region (including the Eastern Black Sea Basin (EBSB) and Eastern Pontides (EP)) has been revealed using inversion of single-station, fundamental-mode Rayleigh-wave group velocities in the period range of 4–40seconds. We used digital broadband recordings of 13 regional earthquakes that recently occurred in the easternmost EBSB recorded at stations of the Kandilli Observatory and Earthquake Research Institute (KOERI). The average group-velocity-dispersion curves were generated from 26 paths for the EBSB, and 16 paths for the EP, and they were inverted to determine the average 1-D shear-wave structure of the region. We have created a pseudo-section, roughly depicting the crustal structure of the region based on the group velocity inversion results of all station-earthquake paths. The thickness of the sedimentary layer reaches 12km in the center of EBSB (Vs=2.5–3.1km/s) and decreases 4km in the EP. There is a thin sedimentary layer in the EP (Vs=2.7km/s). A consolidated thin crust that exists in the EBSB possesses a high seismic velocity (Vs=3.8km/s). While a thin (∼26km) and transitional crust exists beneath the EBSB, a thick (about 42km) continental crust exists beneath the EP where the Conrad is clearly seen at about a 24km depth. Thick continental crust in the EP region is clearly distinguished from a gradational velocity change (Vs=3.4–3.8km/s). The Moho dips approximately southwards, and the Vs velocity (4.25–4.15km/s) beneath the Moho discontinuity decreases from the EBSB to the EP in the N–S direction. This may be an indication of a southward subduction.

Northern Aegean Earthquake (Mw=6.9): Observations at three seismic downhole arrays in Istanbul

The Northern Aegean Earthquake (Mw=6.9\\ML=6.5) took place on May 24, 2014 between the islands of Gokceada, Turkey and Samothraki, Greece. The tremors were felt as far as in Istanbul, about 300km on the East – Northeast (ENE) side of the epicenter. Kandilli Observatory and Earthquake Research Institute (KOERI) of Bogazici University, Turkey operate three downhole arrays in Istanbul, namely Atakoy (ATK), Fatih (FTH) and Zeytinburnu (ZYT) arrays. In this study, waveforms and site response observed at the KOERI operated seismic downhole arrays during the May 2014 Northern Aegean Earthquake (NAE2014) are analyzed in detail and presented. Evaluation of the acceleration records have shown low amplitude but long period and long duration motions at Istanbul. Furthermore, the analyses of the recordings suggest that Vs30 alone may not be a sufficient parameter for the characterization of site amplification.

Regression Relations for Conversion of Various Magnitude Types and Catalogs for the Earthquakes of Turkey and Vicinity

Online Material: Table of regression parameters. Homogeneous earthquake catalogs are needed for various seismological studies, such as hazard analysis and seismicity. In most of the research in question, it is preferred to use moment magnitude M w. Turkey is a seismically active region due to the complex tectonic structure. This high seismicity requires studies on earthquakes that in turn must rely on a uniform catalog, that is, the catalog must be based on a single‐magnitude type. Several national and international organizations record and evaluate the earthquake data to calculate and catalog the magnitude values in various types. This study was carried out to introduce the regression relations between these magnitude scales to provide uniform catalogs for Turkey. A number of studies have been implemented to estimate the relationship between various magnitude scales for global and regional datasets. Although the moment magnitude is the most reliable magnitude scale (Kagan, 2002b, 2003; Castellaro et al. , 2006), it is the most rare. In the regional earthquake catalog of Turkey, compiled by Bogazici University Kandilli Observatory and Earthquake Research Institute–National Earthquake Monitoring Centre (B.U.KOERI–NEMC), there are 2110 body‐wave magnitudes, 1958 local magnitudes, 1511 duration magnitudes, 405 moment magnitudes, and 254 surface‐wave magnitude values published (all magnitudes equal or greater than 4.0) for 4074 events within the period from 1900 to 2014. Similarly, there is a shortage of moment magnitude data in the catalogs of the International Seismological Centre (ISC). A search of the ISC bulletin for events in Turkey with magnitude equal or greater than 4.0 yielded 4246 body‐wave magnitude and 636 surface‐wave magnitude values. There are only 151 moment magnitude reported in the Global Instrumental Earthquake Catalogue released by the ISC and Global Earthquake Model (GEM) effort. With the same search parameters, there are 219 earthquakes with moment magnitude values …

Depremselliğin Fraktal Boyutu ve Beklenen Güçlü Depremlerin Orta Vadede Bölgesel Olarak Tahmini Üzerine Bir Modelleme: Doğu Anadolu Bölgesi, Türkiye

In the scope of this study, a modeling on the fractal dimension which is a measure of the complexity in the occurrence process of earthquakes and intermediate-term forecasting for the location of expected earthquakes for the Eastern Anatolian region (Turkey) were accomplished. For this purpose, the most suitable and reliable statistical relation was firstly tried to be determined between the seismotectonic b-value and fractal dimension Dc-value for the earthquakes in Eastern Anatolian region. Four different methods were applied for this application as; (1) Least Squares Regression (L2 norm), (2) Least Sum of Absolute Deviations Regression (L1 norm), (3) Orthogonal Regression (Total Least Squares) and, (4) Robust Regression. Also, a composite forecast map by combining the maps of relative intensity and pattern informatics is generated for the forecasting the locations of expected strong earthquakes in the Eastern Anatolian region. Earthquake catalogue used for the analyses was compiled from the Kandilli Observatory and Earthquake Research Institute. Catalogue is homogeneous for duration magnitude, MD and consists of 30462 earthquakes with magnitudes between 1.0 and 6.6 in the period between January 1, 1970 and January 1, 2014. As the primary goal, it is intended to put forward the nature of seismicity which has a fractal structure in space, time and magnitude distributions, as quantified by the fractal dimension Dcvalue and seismotectonic parameter b-value for the Eastern Anatolian region. The Eastern Anatolian region was divided into 19 different seismotectonic sub-regions in order to make a detailed assessment on a regional scale. In order to calculate more up-to-date and reliable statistical relation between two seismotectonic parameters, four different regressions were used. Thus, the relationship of Dc3.070.53*b is computed with a strong negative correlation (r = 0.95) between b-value and Dc-value for the Western Anatolia earthquake distributions. For each regression, following linear relations with their correlation coefficients were estimated: Dc 2.490.34*b, for Robust Regression (r = -0.85) Dc 2.510.35*b, for Orthogonal Regression (r = - 0.89) Although the results are very close to each other, using the Least Sum of Absolute Deviations Regression method, the relationship of Dc2.520.36*b with a strong negative correlation (r=-0.91) is obtained between Dc-value and b-value for the Eastern Anatolian region. This negative relationship is important with respect to seismotectonic and an earthquake risk can be mentioned for the Eastern Anatolian region in intermediate-term. Also, this statistical relation is in accordance with the other regional relationships existing in literature and it can be suggested as more up-to-date and reliable. As the secondary purpose, it is intended to generate a composite forecast map based on the earthquake intensities and pattern informatics for the Eastern Anatolian region. For the analyses, the earthquakes with the cut-off magnitude Mc≥3.4 and with depths shallower than 40 km in time interval between 1990 and 2014 were used. For the regional imaging of the forecasting map, a regional grid of points with a grid of 0.075 by 0.075 was used and it is tried to forecast the locations of earthquakes with MD5.0. In the forecasting time interval between January 1, 1970 and January 1, 2024, the composite forecast map was prepared in order to detect the location of expected strong earthquakes in intermediate-term in the Eastern Anatolian region. In the result of analysis, some areas in the Eastern Anatolian region were detected as hazardous regions in terms of earthquake potential in the next. These regions are in and around Askale fault, the west of Van Lake (between Suphan fault and Ercis fault), around Yuksekova-Semdinli fault zone, around and the north part of Ovacik fault, on and southwest end of the Eastern Anatolian fault and, a part of North Anatolian fault zone between Mus Thrust zone and Pulumur fault. Consequently, it is suggested that a special caution should be given to the anomalies in these regions and it must be evaluated with the other geophysical methods together by monitoring the earthquake activity

Deep-Water Characteristics of the Trans-Pacific Tsunami from the 1 April 2014 M w 8.2 Iquique, Chile Earthquake

The sea level data used in this study were provided through the USA National Oceanographic and Atmospheric Administration (NOAA). We thank Hiroshi Tsuruoka and Takeo Ishibe at the Earthquake Research Institute (ERI) for assisting in preparation of some figures. Several figures were drafted using the GMT software (Wessel and Smith 1991). We are sincerely grateful to Prof. Alexander Rabinovich, the editor, and two anonymous reviewers for comments that improved this article. This study is supported by the Japan Society for the Promotion of Science (JSPS).

Comment on “Preseismic ionospheric electron enhancements revisited” by K. Heki and Y. Enomoto

Comment on “Preseismic ionospheric electron enhancements revisited” by K. Heki and Y. Enomoto

Spectral determination of source parameters in the Marmara Region

Ever since the 1999 Kocaeli earthquake, in which the Kandilli Observatory and Earthquake Research Institute (KOERI) was not able to correctly reflect the magnitude size in its preliminary report because of the saturation effect, a rapid and accurate determination of the earthquake becomes a very important issue. Therefore, in the framework of this study, an automatic determination of the moment magnitude was performed by using the displacement spectra of selected earthquakes in the Marmara Region. For this purpose, 39 three-component broadband stations from KOERI seismic network which recorded 174 earthquakes with magnitudes 2.5 ≤ M ≤ 5.0 in between 2006–2009 were used. Due to the importance of quality factor in determination of the moment magnitude with spectral analysis method, the quality factor was calculated for the whole region in the beginning. Source spectrum which was obtained by converting the velocity records to displacement spectra and moment magnitudes of earthquakes were determined by fitting this spectrum to classical Brune model. For this aim, an automatic procedure was utilized which based on minimizing the differences between observed and synthetic source spectra identified by the S waves. Besides moment magnitude and location parameters, some source parameters such as seismic moment, spectral level, corner frequency and stress drop were also calculated. Application of the method proves that determining the seismic moment from the source spectra is applicable not only for earthquakes with small magnitude but also moderate earthquakes as well.

Source characteristics and Coulomb stress change of the 19 May 2011 Mw 6.0 Simav–Kütahya earthquake, Turkey

On 2011 May 19, Simav district of Kütahya province in northwest Anatolia was hit by a moderate size (Mw=6.0) earthquake. Centroid moment tensors for 41 events with moment magnitudes (Mw) between 3.5 and 6.0 are computed by applying a waveform inversion method on data from the Kandilli Observatory and Earthquake Research Institute broadband seismic network. The time span of data covers the period between 2011 May 19 and 2011 August 22. The mainshock is a shallow focus normal event at a depth of 10km. Focal depths of aftershocks range from 5 to 20km. The seismic moment (Mo) of the mainshock is calculated 1.15×1018Nm. The estimated rupture duration of the Simav mainshock is 30s. The focal mechanisms of the aftershocks are mainly normal faulting with a variable strike-slip component. The geometry of focal mechanisms reveals a normal faulting regime with NE–SW trending direction of T-axis in the entire activated region. A stress tensor inversion of focal mechanism data is performed to acquire a more accurate picture of the Simav earthquake stress field. The stress tensor inversion results indicate a predominant normal stress regime with a NW–SE oriented maximum principal compressive stress (σ1). According to high-resolution hypocenter relocation of the Simav seismic sequence, two main clusters are revealed. The aftershock activity in the observation period between 2011 May 19 and 2011 August 22 extends from the mainshock cluster to the NE direction. Seismic cross-sections indicate that a complex pattern of the hypocenter distribution with the activation of two nearly parallel faults. The northern cluster is associated with a fault plane trending mainly E–W and dipping towards SE, while the southern is related to a fault plane trending NW–SE and dipping towards SE. The best constrained focal depths indicate that the aftershock sequence is mainly confined in the crust (depth<25km) and is operating in the approximate depth range from 2 to 24km. Consequently, Coulomb stress analysis is performed to calculate the stress transfer and correlate it with the activated region. Positive lobes with stress more than 3 bars are obtained, indicating that these values are large enough to increase the Coulomb stress failure towards NW–SE direction.

Marmara Bölgesinde Ampirik Green Fonksiyon Yöntemiyle Deprem Benzeşimlerinin Elde Edilmes

The main purpose of this article is to simulate three mid-sized earthquakes that occurred in Marmara Sea region, which has complex geologic and tectonic characteristics resulting in heterogeneous crustal structure. In the calculation of earthquake simulations, the method based on empirical Green’s function (EGF) developed by Hutchings and Wu (1990) is used. In this way, we evaluate the achievements in simulating ground motion waveforms using empirical Green’s function method especially for Marmara region where complex geologic structure exists. The main assumption of the method that simple rupture models and small sized earthquakes (impulsive point source event) recorded in the region can be used as an empirical Green’s functions to simulate earthquake ground motions. Accurate estimation of strong motion time history simulation is essential to establishing the recent technology of the earthquake-resistant design and performance based design of structure to reduce earthquake damage. The main reason of this, non-linear dynamic analysis of structures in time domain needs synthetic accelerograms as an input. We simulate three earthquakes (Mw≈5) that occurred along three different extensions of the North Anatolian Fault Zone (NAFZ) inside of the Marmara Sea. The first one occurred on the northern branch of the NAFZ, in northern part of the Marmara Sea, the second one was along the mid-branch of NAFZ that bissects the Gulf of Gemlik and the last one took place on the southern branch of NAFZ in the vicinity of Kus Lake south of the terrestrial areas of the Marmara Sea. Earthquakes used in the study were recorded by broadband seismometer network operated by Kandilli Observatory and Earthquake Research Institute (KOERI). Modelling was made for each earthquake using by five stations, each of which recorded at least one after shock and one main shock, in total ten stations. The distance between recording stations and earthquake hypocenters ranged from 17 km to 121 km. The distance between the simulated earthquake hypocenter and EGF hypocenter ranged from 0.73km to 1.64 km. Similarities between recorded and simulated waveforms were investigated in terms of different parameters such as first arrivals of P waves, time differences between S and P wave arrivals, recording duration, maximum ground velocity, Fourier spectrum and energy distribution. The results confirm that empirical Green’s function method is an appropriate method to obtain ground motion simulations especially in areas such as Marmara region which has a heterogeneous crust structure

Application of Discrimination Filter Based on the Polarization to the Surface Wave Records

As well known, each type of seismic waves has a specific particle motion. The basic surface waves Love and Rayleigh show the particle motions polarized linearly in the transversal-horizontal plane and elliptically in the vertical-radial plane, respectively. Like in the body waves, polarization properties can be used to design the surface wave discrimination filter. The process consists of weighting the amplitudes of vertical (Z), radial (R) and tangential (T) components of the ground motion at each frequency according to the particle motion. The weighting process is applied to entire length of each component for selected window length and moving interval, but weights are not applied to the original phase values. The weighted parts for each window are transformed to the time domain and filtered signals are obtained as the arithmetic average of values of the overlapping points. The method has been applied to the broad-band digital three-component records at stations having about 10° epicenter distances of Bogazici University Kandilli Observatory and Earthquake Research Institute (KOERI) of Erzurum earthquakes and noticed that the window length and moving interval in proportion to epicenter distance affect the results on a large scale. For the cases in which the best results are obtained, it has been determined that the ratio between the window length and moving interval for increased epicenter distances are 3.95, 4.5 and 4.8, respectively.

Determination of the Crust and Upper-Mantle Structure in Anatolia by Surface Wave Data

In this study, the crust and upper mantle structure of Anatolia have been investigated by measuring the group velocity dispersion data of discriminated seismic surface waves. In the scope of the study, it has selected the profiles between six stations located in western Anatolia of Bogazici University Kandilli Observatory Earthquake Research Institute, national network of Turkey, and records of an earthquake (having about 10° epicentral distance) occurred in the eastern of Anatolia have been used. Firstly, surface wave discrimination filter based on the polarization properties has been applied tothree-component recordsand emphasized to surface waves. Then the group velocities have been calculated by multiple filter technique. A five-layered crustal model having total thickness of 38 - 40 km and Pn-wave velocity of 8.00 km/sec in the upper-mantle has been determined through inversion of surface wave group velocity dispersion data in the period range of 10 sec to 60 sec.

Source mechanism and stress analysis of 23 October 2011 Van Earthquake (Mw = 7.1) and aftershocks

On 23 October 2011 at 1341 local time, a strong earthquake (Mw = 7.1) occurred east of Lake Van (KOERI; Kandilli Observatory and Earthquake Research Institute). The focal parameters of the main shock and 29 aftershocks with M ≥ 4.0 were obtained from regional broadband seismic data from KOERI network by using Regional Moment Tensor Inversion Code (Dreger 2002). It is confirmed that the main shock had thrust faulting mechanism. The stress tensor analysis was completed using the focal mechanism solutions and the software developed by (Gephart Comp Geosci 16: 953-989, 1990). The maximum principal stress (P compressional) of the main shock is aligned in a N-S (NNW/SSE) direction and the tensional axis (T dilatation) is aligned in an E-W (ENE-WSW) direction. The b value is calculated as 0.96 using the maximum likelihood method (Utsu 1999).