TÜRKİYE VE C İVARINDAKİ FARKLI S İSMİK BÖLGELER İÇİN ...kocaeli2007.kocaeli.edu.tr/kocaeli2007/TAM_METIN_NUMARALI-SIR… · 92 tÜrkİye ve cİvarindakİ farkli sİsmİk

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TÜRKİYE VE CİVARINDAKİ FARKLI SİSMİK BÖLGELER İÇİN ALETSEL VERİYE DAYALI DEPREM HAZARD PARAMETRELERİNİN BİR DEĞERLENDİRMESİ

AN EVALUATION OF EARTHQUAKE HAZARD PARAMETERS BASED ON THE INSTRUMENTAL DATA FOR DIFFERENT SEISMIC REGIONS OF TURKEY AND ADJACENT AREAS

Yusuf Bayrak1, Serkan Öztürk1, Theodoros M. Tsapanos2, George Ch. Koravos2, Georgios A. Leventakis2, Doğan Kalafat3

1Karadeniz Technical University, Department of Geophysics, Trabzon, Turkey

2Aristotle University of Thessaloniki, School of Geology, Geophysical Laboratory, Greece

3Boğazici University, Kandilli Observatory and Earthquake Research Institute, İstanbul, Turkey

E-posta: [email protected]

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Anahtar Kelimeler: Türkiye, maksimum bölgesel magnitüd, ortalama aktivite oranı, K indeksi

ÖZ Bu çalışmada, maksimum olasılık yöntemi kullanılarak Türkiye ve civarı için maksimum bölgesel magnitüd maxM̂ ve ortalama aktivite oranı λ̂ gibi deprem hazard parametrelerinin bir değerlendirmesi yapılmıştır. Ayrıca, deprem hazard seviyesi göreceli deprem hazard ölçeğinin bir fonksiyonu olarak (K indeksi olarak tanımlanmıştır) hesaplanmış ve her bir bölge için haritalanmıştır. Çalışmada kullanılan veri KOERI ve ISC kataloglarından derlenmiştir. 7.50’den büyük en yüksek maxM̂ değerleri Kuzey Anadolu Fay Zonu boyunca ve Ege arkında bulunmuştur. 100’den büyük en yüksek λ̂ değerleri o bölgelerdeki belirgin bir magnitüd değeri üzerindeki olayların sayısındaki artışa bağlı olarak Sultandağı, Beyşehir ve Tatar faylarında, Bitlis Bindirme Zonunda ve Doğu Anadolu Fay Zonunda hesaplanmıştır. Ayrıca, en büyük K indeksi 6’ya eşittir ve Kuzey Anadolu Fay Zonunun orta kısmı ile Ege Arkında gözlenmiştir.

Key words: Turkey, the maximum regional magnitude, the mean activity rate, index K

ABSTRACT In this study, using the maximum likelihood method an evaluation of earthquake hazard parameters such as the maximum regional magnitude, maxM̂ , and the mean activity rate, λ̂ , is made for Turkey and adjacent areas. The earthquake hazard level is also calculated as a function of relative earthquake hazard scale (defined as an index K) and is mapped for each region. The data used in this study is compiled from the catalogues of KOERI and ISC. The largest maxM̂ values greater than 7.50 are found in the Aegean Arc and along the North Anatolian Fault Zone. The largest λ̂ values greater than 100 are computed in Sultandağı, Beyşehir and Tatar faults, Bitlis Thrust Zone, and East Anatolian Fault Zone depending on the great number of events above a certain magnitude per year in these regions. Also, the largest index K is equal to 6 and observed in the middle part of North Anatolian Fault Zone and Aegean Arc.

INTRODUCTION

Numerous seismic hazard studies have been made in order to estimate the earthquake hazard in Turkey using the statistical processing of the instrumental earthquake data

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(Båth 1979; Erdik et al., 1999; Bayrak et al., 2005). Although many reports are known that Turkish instrumental records are far from being incomplete for probabilistic approach of seismic hazard, an effort is undertaken for such analysis in the present study. Thus, we aimed to evaluate the earthquake hazard parameters such as the maximum regional magnitude, maxM̂ , the mean activity rate, λ̂ , and the relative earthquake hazard scale, index K, for Turkey and adjacent areas.

DATA USED and METHOD

The earthquake data used in this study is compiled from the Boğaziçi University, Kandilli Observatory and Earthquake Research Institute (KOERI) and the International Seismological Center (ISC) and historical catalogue of KOERI. There are 2398 events between 1900 and 1974 and 68478 events between 1974 and 2005. The catalogue is uniform of surface magnidude (MS). The final data between the time interval 1900-2005 and shallow earthquakes (depth<60 km) including 69339 events are used for the calculations. Analysis is carried out in a rectangular area limited by the co-ordinates 25oE and 45oE in longitude and 33oN and 43oN in latitude. The seismic source zones considered in this study are defined according as the major fault systems and seismicity of Turkey as well as the studies and seismic source zones made by other authors (Erdik et. al., 1999; Bayrak et al., 2005). Thus, Turkey was divided into 24 seismic regions. Figure 1 shows the seismic regions with the tectonic structures and the epicenters of earthquakes in Turkey from 1900 to 2005.

A large number of earthquake occurrence models are currently available for seismic hazard estimation. One of the most popular components of the earthquake hazard assessment is the appraisal of the maximum regional magnitude and the relative earthquake hazard level of a specific region. In order to estimate the maximum regional magnitude, maxM̂ , it is used the method given by Kijko, (1988) while the mean activity rate, λ̂ , is computed by the method proposed by Kijko and Sellevoll (1989; 1992), and Kijko and Graham (1998). In order to classify the examined regions in groups, based on their difference in the hazard level, we follow the technique used by Tsapanos (2001). Regional variation maps of maxM̂ value and K index are drawn with different grey scale and shown in Figures 2 and 3, respectively.

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Figure-1. Different source regions considered in this study together with the major tectonic structures. Epicenter distributions of earthquakes of MS between 4.0 and

8.0 for the time period 1900-2005 are also shown.

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Figure-2. maxM̂ (the maximum regional magnitude) values for different 24 seismic source regions in Turkey and adjacent areas.

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Figure-3. K index (relative hazard level) values for different 24 seismic source regions in Turkey and adjacent areas.

CONCLUSIONS

In this study, an effort is made for the evaluation of earthquake hazard parameters such as the maximum regional magnitude, maxM̂ , mean activity rate, λ̂ , and relative earthquake hazard scale, index K, for Turkey and adjacent areas. For this purpose, it is used the different methods proposed by some authors. Turkey was divided into 24 different regions taking into account the different zonation studies made by several authors for modeling of seismic hazard in Turkey, and plotting the existing tectonic structure with the episantr distribution of earthquakes. The data used in this study includes the instrumental period between 1900 and 2005 and taken from the Boğaziçi University, Kandilli Observatory and Earthquake Research Institute and the International Seismological Center and historical catalogue of KOERI. The catalogue has 2398 events between 1900 and 1974 and 68478 events between 1974 and 2005. For the calculations, it is used the shallow earthquakes (depth<60 km) including 69339 events between the time interval 1900 and 2005 and the catalogue is homogeneous for MS. We used a rectangular area limited by the co-ordinates 25oE and 45oE in longitude and 33oN and 43oN in latitude. The earthquake hazard parameters such as the maximum regional magnitude and the mean seismic activity rate are estimated by the maximum likelihood method for whole Turkey. Also, the earthquake hazard level is calculated as a function of relative earthquake hazard scale (defined as an index K) and mapped for each seismic region. Consequently, it is observed the largest maxM̂ values greater than 7.50 in the Aegean Arc and along the North Anatolian Fault Zone. The largest λ̂ values greater than 100 are computed in Sultandağı, Beyşehir and Tatar faults, Bitlis Thrust Zone and East Anatolian Fault Zone depending on the great number of events above a certain magnitude per year in these regions. Also, the largest index K is observed in the middle part of North Anatolian Fault Zone and Aegean Arc. Thus, the distribution of hazard level from region to region is informative and useful from a practical point of view. REFERENCES

Båth, M., 1979, Seismic risk in Turkey; a preliminary approach, Tectonophysics, 54, T9-T16

Bayrak Y., Yılmaztürk, A., and Öztürk, S., 2005, Relationships between fundamental seismic hazard parameters for the different source regions in Turkey, Natural Hazards, 36, 445-462

Erdik, M., Alpay, B. Y., Onur, T., Sesetyan, K., and Birgoren, G., 1999, Assessment of earthquake hazard in Turkey and neighboring regions, Annali di Geofisica, 42, 1125-1138

Kijko, A., 1988, Maximum likelihood estimation of Gutenberg-Richter b parameter for uncertain magnitudes values, Pageoph., 127, 573-579

Kijko, A., and Sellevoll, M. A., 1989, Estimation of earthquake hazard parameters from incomplete data files. Part I. Utilization of extreme and complete catalogs with different threshold magnitudes, Bull. Seismol. Soc. Am., 79, 645-654

Kijko, A., and Sellevoll, M. A., 1992, Estimation of earthquake hazard parameters from incomplete data files. Part II. Incorporation of magnitude heterogeneity, Bull. Seismol. Soc. Am., 82, 120-134

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Kijko, A., and Graham, G., 1998, ‘Parametric-historic’ procedure for probabilistic seismic hazard analysis. Part I. Estimation of maximum regional magnitude mmax, Pageoph., 152, 413-442

Tsapanos, T. M., 2001, Evaluation of the seismic hazard parameters for selected regions of the world: the maximum regional magnitude, Annali Di Geofisica, 44, N.1