P33 Correlation between the Values of b and DC for the Different Regions in the Western Anatolia

Transcription

1 P33 Correlation between the Values of b and DC for the Different Regions in the Western Anatolia E. Bayrak* (Karadeniz Technical University) & Y. Bayrak (Karadeniz Technical University) SUMMARY The b-value and fractal dimension Dc calculated for different regions and to investigate relation between b-value and Dc value in the Western Anatolian (WA). The whole examined area is divided into 15 seismic regions based on their seismotectonic regime. The data used in this work was taken from different sources and catalogues. The technique of maximum likelihood method is applied to evaluate the b-value. Dc value is estimated using the correlation dimension. The b values change between 0.71 and The values smaller than 0.80 are computed in regions of 10 and 12 which are related the Aegean Arc. The higher values are found in the regions 2 and 7 covering Akhisar and Karova-Milas and Muğla-Yatağan Fault zones. Dc values change between 1.69 and The higher values of Dc are calculated in regions of 1, 15, 14, 10, 4 and 5 related different tectonic mechanisms. The smaller Dc values are computed in regions of 13, 7 and 6. The correlation between b-value and Dc value is determined with 95% confidence limit. We obtained negative relation between b and Dc values for Western Anatolia. Using the least squares method, we obtained the regression function of the first order DC= b.

2 Introduction The Western Anatolian (WA) is one of the most seismically active and rapidly prolongating areas of the Eastern Mediterranean region (e.g., Bozkurt 2001). Aegean Subduction Zone at the south where the African Plate subducting beneath the Anatolian Plate and N-S trending extensional zone are main tectonic features of this area. Active normal faults related to grabens and horsts and strike-slip faults are dominant in WA. Many quantitative techniques have been applied over the years to present the geographical distribution of earthquake hazard in several regions of the Earth and Turkey (e.g. Tsapanos, 2001; Bayrak et al., 2005). Turkey is situated in a very active seismic region, so the earthquake hazard in Turkey has therefore been widely studied using a number of different techniques and seismic quantities (e.g. Kayabalı and Akın, 2003; Bayrak et al., 2008). The correlation dimension (D C ) (Grassberger and Procaccia, 1983) measures the spacing or clustering properties of a set of points and is often used to characterize the distribution of earthquake epicenters (Kagan and Knopoff, 1980; Hirata, 1989b). The spatial distribution of an earthquake epicenter has a fractal structure (Kagan and Knopoff, 1980; Sadovskiy et al., 1984). Analysis of the correlation between fractal attributes of complex seismotectonic variables may offer insights into seismic hazard assessment. Regional variation in the correlation dimension of epicenters (D C ) is found, in several studies, to correlate negatively with the b-value in different regions of the world (Hirata 1989, Öncel and Wilson 2002). The goal of the present study is to calculate b-value and D C value for different regions in Western Anatolia and to investigate relation between b-value and D C value. Method and Data The data used in this study was taken from different sources and catalogues such as TURKNET, International Seismological Centre (ISC), Incorporated Research Institutions for Seismology (IRIS) and The Scientific and Technological Research Council of Turkey (TUBITAK) and provided in different magnitude scales. The catalogues contain the origin time, different magnitudes scales (m b - body wave magnitude, M S -surface wave magnitude, M L -local magnitude, M D -duration magnitude, and M W -moment magnitude), epicenter and depth information of earthquakes. Turkey earthquake catalogue, obtained from the Boğaziçi University, Kandilli Observatory and Earthquake Research Institute (KOERI), starts from 1974 until The earthquakes from 1900 to 1974 come from the International Seismological Centre (ISC) and instrumental catalogue of KOERI. The earthquake catalogue used in this study is being compiled by Erdik et al. (1999). Bayrak et al. (2009) developed some relationships between different magnitude scales in order to prepare a homogenous earthquake catalogue from different data sets. We prepared a homogenous earthquake data catalogue for M S magnitude using these relationships. A complete understanding of the instrumental seismicity, tectonics, geology, paleoseismology, and other neotectonic properties of the considered region are necessary for an ideal delineation of seismic source zones. In this study, we divided Western Anatolian (WA) into fifteen seismic zones for detailed study as seen in Figure 1. The epicentral distributions of the instrumental earthquakes are shown in Figure 1 on different seismic source zones in WA. The b-value in Gutenberg and Richter s relation:, where a and b are constants. The constant b is the slope of the log-linear relation and is known as b- value (Scholz 1990; Wiemer and Wyss 1997). The b-value of any region can be computed using several methods like linear least squares regression or by the MLM. The most robust and widely accepted method is the Maximum Likelihood Method (MLM) where the b-value is calculated using the formula (Aki 1965); where is the average magnitude and is the minimum value of the magnitude presenting the data. The fractal dimension, the D C value, is estimated using the correlation dimension. The

3 correlation dimension as defined by Grassberger and Procaccia (1983) measures the spacing of a set of points, which in this case are the earthquake epicenters. The correlation integral technique that gives the correlation dimension is preferable because of its greater reliability and sensitivity to small changes in clustering properties (Kagan and Knopoff, 1980; Hirata, 1989). The correlation integral is given by Grassberger and Procaccia (1983) as, where (Cr) is the correlation function. The correlation function measures the spacing or clustering of a set of points and is given by the relation 2 C( r) N( R r) NN ( 1) where N(R<r) is the number of pairs (Xi, Xj) with a smaller separation than r. The correlation integral is related to the standard correlation function as given by Kagan and Knopoff (1980): where D C is a fractal dimension, more strictly, the correlation dimension (Grassberger and Procaccia, 1983). If the earthquakes become progressively more clustered, the value of D C decreases. Smith (1988) suggested that a large number of datasets are required for the accurate estimation of D C. The distance (r) between two events (θ 1, ϕ 1 ) and (θ 2, ϕ 2 ) is calculated by using a spherical triangle as given by Hirata (1989): where θ 1 and θ 2 are the latitudes and ϕ 1 and ϕ 2 are the longitudes of the event 1 and event 2, respectively. D C is estimated as the slope of log 10 C(r) versus log 10 r using the least-squares (LS) method. Figure 1. Earthquake epicenters, tectonics and different 15 seismic regions in the Western Anatolia. (Region 1- Aliağa Fault, Region 2- Akhisar Fault, Region 3- Eskişehir, İnönü Dodurga Fault zones, Region 4- Gediz Graben-Dumlupınar Fault, Region 5- Simav, Gediz-Dumlupınar Faults, Region 6- Kütahya Fault Zone, Region 7- Karova-Milas, Ula Ören, Muğla-Yatağan Faults, Region 8- Büyük Menderes Graben, Region 9- Dozkırı-Çardak, Sandıklı Faults, Region 10- Aegean Islands, Region 11- Aegean Arc, Region 12- Marmaris, Köyceğiz, Fethiye Faults, Region 13- Gölhisar-Çameli, Acıgöl, Tatarlı Kumdanlı Faults, Dinar Graben, Region 14- Sultandağı Fault, Region 15- Beyşehirgölü, Kaş Faults

4 (a) (b) Figure 2. Mapped of b and D C values for different seismic regions and tectonics Conclusions To evaluated to b-values and fractal dimension, we used to ZMap program (Wiemer, 2001). The computed b and D C -values mapped in Figure 2. We clearly see that in this figure, b and D C -values related to each other oppositely. These observations suggest that different regions are under different stress conditions. The computed b-values change between 0.71 and 1.02 for the different 15 regions in WA. The values smaller than 0.80 are computed in regions of 10 and 12 which are related the Aegean Arc. The higher values are found in the regions 2 and 7 covering Akhisar and Karova-Milas and Muğla-Yatağan Fault zones. The observed values in the graben sytems such as Gediz and Büyük Menderes are greater than The computed D C -values change between 1.69 and 2.27 for the different 15 regions in WA. The higher values of D C are calculated in regions of 1, 15, 14, 10, 4 and 5 related different tectonic mechanisms. The smaller D C values are computed in regions of 13, 7 and 6. Figure 3. Correlation between b and D C values with 95% confidence limit (D C = b).

5 The correlation between b-value and D C value is determined with 95% confidence limit. We obtained negative relation between b and D C values for Western Anatolia. Plot of this correlation is in Figure 3. Using the least squares method, we obtained the regression function of the first order D C = b This function is concordance with Hirata (1989) s relation (D C = b). Acknowledgements The authors are grateful to Karadeniz Technical University (Turkey) for partially supporting this work (project number: ). References Aki, K. [1965] Maximum likelihood estimate of b in the formula log N = a - bm and its confidence limits, Bull. Earthquake Res. Inst., Tokyo Univ. 43, Bayrak, Y. Yılmaztürk, A. and Öztürk, S. [2005] Relationships between fundamental seismic hazard parameters for the different source regions in Turkey, Natural Hazards, 36, Bayrak, Y. Öztürk, S. Koravos, G.Ch. Leventakis, G.A. and Tsapanos, T.M. [2008] Seismicity assessment for the different regions in and around Turkey based on instrumental data: Gumbel first asymptotic distribution and Gutenberg-Richter cumulative frequency law, Natural Hazards and Earth System Sciences, 8, Bayrak, Y. Öztürk, S. Çınar, H. Kalafat, D. Tsapanos, T.M. Koravos, G.Ch. and Leventakis, G.A. [2009] Estimating earthquake hazard parameters from instrumental data for different regions in and around Turkey, Engineering Geology, 105, Bozkurt, E. [2001] Neotectonics of Turkey- a Synthesis. Geodinamica Acta, 14, Erdik, M. Alpay, BY. Onur, T. Sesetyan, K. and Birgoren, G. [1999] Assessment of earthquake hazard in Turkey and neighboring regions. Annali di Geofisica, 42, Grassberger, P., Generalized dimensions of strange attractors, Phys. Lett. A, 97, , Grassberger, P., and I. Procaccia [1983] Measuring the strangeness of strange attractors, Physica D, 9, Hirata, T. [1989] Fractal dimension of fault system in Japan: Fractal structure in rock fracture geometry at various scales, Pure Appl. Geophys., in press. Kagan, Y. Y., and L. Knopoff [1980] Spatial distribution of earthquakes: The two-point correlation function, Geophys. J. R. Astron. Soc., 62, Kayabalı, K. and Akin, M. [2003] Seismic hazard map of Turkey using the deterministic approach. Engineering Geology, 69, Öncel, A.O., Wilson, T. [2002] Space-Time Correlations of Seismotectonic Parameters and examples from Japan and Turkey Preceding the Izmit Earthquake, Bulletin Seismological Society of America, 92, Sadovskiy, M. A., T. V. Golubeva, V. F. Pisarenko, and M. G. Shnirman [1984] Characteristic dimensions of rock and hierarchical properties of seismicity, Izv. Acad. Sci. USSR Phys. Solid Earth, Engl. Transl., 20, Scholz, C.H. [1990] The Mechanics of Earthquakes and Faulting. xxii pp. Cambridge, New York, Port Chester, Melbourne, Sydney: Cambridge University Press. ISBN Tsapanos, T.M. [2001] Evaluation of seismic hazard parameters for selected regions of the world: the maximum regional magnitude, Annali di Geofisica, 44, Wiemer, S., and M. Wyss [1997] Mapping the frequency-magnitude distribution in asperities: An improved technique to calculate recurrence times?, J. Geophys. Res., 102, Wiemer, S. [2001] A software package to analyze seismicity: ZMAP, Seism. Res. Lett., 72,