Temporal and spatial variations of Gutenberg-Richter parameter and fractal dimension in Western Anatolia, Turkey

Accepted Manuscript Temporal and Spatial Variations of Gutenberg-Richter Parameter and Fractal Dimension in Western Anatolia, TURKEY Erdem Bayrak, Şeyda Yılmaz, Yusuf Bayrak PII: DOI: Reference:

S1367-9120(17)30039-1 http://dx.doi.org/10.1016/j.jseaes.2017.01.031 JAES 2949

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Journal of Asian Earth Sciences

Received Date: Revised Date: Accepted Date:

21 June 2016 17 January 2017 26 January 2017

Please cite this article as: Bayrak, E., Yılmaz, S., Bayrak, Y., Temporal and Spatial Variations of Gutenberg-Richter Parameter and Fractal Dimension in Western Anatolia, TURKEY, Journal of Asian Earth Sciences (2017), doi: http://dx.doi.org/10.1016/j.jseaes.2017.01.031

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Temporal and Spatial Variations of Gutenberg-Richter Parameter and Fractal Dimension in Western Anatolia, TURKEY

Erdem Bayrak1(*), Şeyda Yılmaz1 , Yusuf Bayrak1 1

Affiliation for author 1. Karadeniz Technical University, Department of Geophysics, Trabzon, Turkey, [email protected]

Corresponding author: E. Bayrak ([email protected])

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Abstract The temporal and spatial variations of Gutenberg-Richter parameter (b-value) and fractal dimension (DC) during the period 1900-2010 in Western Anatolia was investigated. The study area is divided into 15 different source zones based on their tectonic and seismotectonic regimes. We calculated the temporal variation of b and DC values in each region using Zmap. The temporal variation of these parameters for the prediction of major earthquakes was calculated. The spatial distribution of these parameters is related to the stress levels of the faults. We observed that b and DC values change before the major earthquakes in the 15 seismic regions. To evaluate the spatial distribution of b and DC values, 0.500x0.500 grid interval were used. The bvalues smaller than 0.70 are related to the Aegean Arc and Eskisehir Fault. The highest values are related to Sultandağı and Sandıklı Faults. Fractal correlation dimension varies from 1.65 to 2.60, which shows that the study area has a higher DC value. The lowest DC values are related to the joining area between Aegean and Cyprus arcs, Burdur-Fethiye fault zone. Some have concluded that b-values drop instantly before large shocks. Others suggested that temporally stable low b value zones identify future large earthquake locations. The results reveal that large earthquakes occur when b decreases and DC increases, suggesting that variation of b and DC can be used as an earthquake precursor. Mapping of b and DC values provide information about the state of stress in the region, i.e. lower b and higher DC values associated with epicentral areas of large earthquakes. Keywords: Gutenberg-Richter Relation: b-value, Fractal Dimension: DC value, Earthquake Precursor

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1 Introduction The Neotectonic evolution of Turkey has been dominated by the collision of the African and Arabian plates with the Eurasian plate along the Hellenic arc to the west and the Bitlis-Zagros suture zone to the east (Elitok and Dolmaz, 2011). Western Anatolia and the Aegean Sea are commonly considered as under N–S extension in response to westward motion of the Anatolian block which is in a collision with Arabian Plate (McKenzie, 1972; Dewey and Sengor, 1979). The Aegean extension region is one of the most seismically active and rapidly prolonging areas of the Eastern Mediterranean region (Bozkurt, 2001). The large and destructive earthquakes occurred in both historical and instrumental periods in this region. So, this region has been attractive for earthquake hazard and risk studies (Gok et al., 2014, Polat et al., 2008, 2009). Seismic precursory phenomena, e.g. changes of seismic source parameters, seismic quiescence and changes of the magnitude-frequency distribution of earthquakes (b-value) have been studied by previous studies (Kalafat, 2016, Enescu and Ito, 2001, 2002; Wiemer et al., 2005; Wyss and Habermann, 1979). The initial rupture of large earthquakes, by contrast, was found to occur in regions where b-values are low (Wyss and Stefansson, 2006; Wyss et al., 2000). Previous studies (Schorlemmer et al., 2005) pointed out that the region with low b-value implies large differential stress and suggests it's being toward the end of the seismic cycle. The spatial variation of bvalues is related to the distribution of stress and strain (Mogi, 1967; Scholz, 1968), geological complexity (Lopez Casado et al., 1995), material heterogeneity or crack density (Mogi, 1962) and velocity of deformation (Manakou and Tsapanos, 2000). DC is controlled by the heterogeneity of the stress field and the preexisting geological, mechanical or structural heterogeneity (Öncel et al., 1996). Wyss and Lee (1973) observed a decrease in b-value before several earthquakes in California. Chen et al. (1984b) observed a decrease in b-value before the

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M 7.1 Zhao-tong earthquake of 11 May 1974. Nanjo et al. (2012) observed a decrease in b-value in the source regions prior to the 2004 M 9.2 Sumatra and 2011 M 9 Tohoku earthquakes. Their observations were different from those by Das Gupta et al. (2007). Schurr et al. (2014) observed a decrease in b value in the source regions prior to the M 8.1 Iquique, Northern Chile, earthquake of 1 April 2014. The main objective of this study is to map the spatial and temporal variations of b and DC values in and around Western Anatolia. In order to calculate these parameters, Zmap software was used (Wiemer, 2001). In the present study, we computed temporal variations of the b and DC values for 15 different seismogenic source zones in WA -Western Anatolia- (Bayrak and Bayrak, 2012a), and also spatial variations of the parameters for Western Anatolia were mapped. 2 Tectonic Setting Main tectonic structures playing important role in the geodynamics evolution of the Aegean region are the Aegean Arc and Western Anatolian Extension Zone. Figure 1 show tectonics structures and focal mechanisms of 190 events (h ≤ 70 km) with 4.7 ≤ mb ≤ 7.1 occurred in the study area (26–33o E, 33–40.5o N) during the period 1953–2010 (Bayrak and Bayrak, 2012a). Fault mechanism solutions were obtained from Tan (2008)’s catalog.

The convergence between the Arabian and Eurasian plates in the Eastern Anatolia pushes the Anatolian Plate westwards along the North Anatolian Fault Zone and the East Anatolian Fault Zone and Anatolian Plate rotates anticlockwise with an average velocity of 24 mm/yr (McClusky et al. 2000). Therefore, the timing of collision-induced westward extrusion of the Anatolian plate has been widely accepted as the commencement of the Neotectonic history of Turkey (Şengör and Yılmaz, 1981; Koçyiğit et al., 2001). The tectonic escape model develops a cause4

effect relationship and describes a process triggered by collision along the Bitlis Suture Zone in Southeast Anatolia in the Middle Miocene resulting in development of the North Anatolian and East Anatolian Fault Zones, western escape of the Anatolian plate, and concluding with the N-S extensional tectonic regime displayed in E-W grabens in Western Anatolia in the Late Miocene (Dewey and Şengör, 1979; Şengör, 1982; Şengör et al., 1985). This motion is transferred into the Aegean in the southwestern direction (McKenzie, 1972, 1978), which results in the northern Aegean being dominated by dextral strike-slip faulting of the northeastern strike. The African Plate subducts beneath the Anatolian Plate in an N-NE direction in the Eastern Mediterranean (McKenzie, 1978). The Aegean arc consists of the outer sedimentary arc and of the inner volcanic arc, while its outer borders are bounded by the Aegean trench with a maximum water depth of 5 km (Papazachos and Kiratzi, 1996). The Western Anatolian is one of the most seismically active and rapidly extending areas in the world (e.g., Bozkurt, 2001). It is currently experiencing an approximately N–S continental extension at a rate of 30–40 mm/year (Oral et al., 1995; Le Pichon et al., 1995). Approximately E–W trending grabens (e.g. Edremit, Bakırçay, Kütahya, Simav, Gediz, Küçük Menderes, Büyük Menderes, and Gökova grabens) and their basin-bounding active normal faults are the most prominent neotectonic features of Western Anatolia (e.g., Şengör et al., 1985; Şengör 1987; Seyitoğlu and Scott, 1992a, b; Koçyiğit et al., 1999; Yılmaz et al., 2000; Lips et al., 2001; Sözbilir, 2001, 2002; Bozkurt and Sözbilir, 2004; Kaya et al., 2004; Erkul et al., 2005; Emre and Sözbilir, 2007). Other, less prominent, structural elements of Western Turkey are the N-NE-trending basins and their intervening horsts e.g. Gördes, Demirci, Selendi, and Uşak-Güre basins; (e.g. Ersoy and Helvacı, 2007). The eastern part of studied region includes the NW–SE trending Dinar, Beyşehir, and Akşehir–Afyon grabens and NE–SW trending Burdur, Acıgöl, Sandıklı, Çivril and Dombayova grabens and their

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bounding faults (e.g., Bozkurt 2001). The existence of two sets of normal faults indicates that the region is extending biaxially, with both NE–SW and NW–SE components of extension (Westaway, 1994). The N–S-striking active normal faults and some NNE–SSW-trending strikeslip faults such as the Orhanlı Fault Zone (OFZ) and the Bergama-Zeytindağ Fault (BZF) zone are also present in the region (Yılmaz et al., 2000; Uzel and Sözbilir, 2008). Other potentially active faults are the Manisa Fault near Manisa city, and İzmir Fault (İF) trending E–W direction (Bozkurt and Sözbilir, 2006). The Karaburun-Gulbahce Fault (KGF) occurs in the Karaburun Peninsula and is supposed to be a predominantly strike-slip fault. Gokova Fault (GF) can be traced on a line trending E–W direction along the northern coast of the Gökova Bay (GB) in the south of Western Anatolian (e.g., Şaroğlu et al., 1992; Eyidoğan, 1988; Ocakoğlu et al., 2004, 2005; Aktuğ and Kılıcoğlu, 2006). This will benefit to the studies in several subjects such as seismic studies, natural hazard and risk assessment, engineering, mineral and oil exploration, researchers of water and geothermal resources and the indirect usage in the cultural heritages and archaeological site investigations and preserves (Akman and Tüfekci, 2004). 3 Methods 3.1 Maximum Likelihood Method The empirical relationship, known as Gutenberg–Richter (G–R) law, between the frequency of earthquake occurrences and magnitudes can be expressed as in the following formula: LogN  a  bM

(1)

where N is the cumulative number of earthquakes with magnitude greater or equal to M, a and b are constants. b is the slope of the frequency–magnitude distribution, and a is the activity level of seismicity. Gutenberg and Richter (1944) firstly, estimated the constants known as seismicity

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parameters. The b-value for a region not only reflects the relative proportion of the number of large and small earthquakes in the region but is also related to the stress condition over the region. Many factors can cause perturbation of the normal b-value. On average, b-value is near unity for most seismically active regions on Earth (Frohlich and Davis, 1993). In a tectonically active region, the b-value is normally close to 1.0 but varies between 0.5 and 1.5 (Pacheco et al., 1992; Wiemer and Wyss, 1997). However, a detailed mapping of b-value often reveals significant deviations. The spatial variation of b-values is related to the distribution of stress and strain (Mogi, 1967; Scholz, 1968). On the other hand, high b values are reported from areas of increased geological complexity (Lopez Casado et al., 1995), indicating the importance of the multi-fracture area. Increased material heterogeneity or crack density results in high b-values (Mogi, 1962). Thus, low b-value is related to the low degree of heterogeneity, large stress and strain, the large velocity of deformation and large faults (Manakou and Tsapanos, 2000). bvalues were first estimated by Gutenberg and Richter (1944) for various regions of the world. They suggested that b-values range from 0.45 to 1.50, while Miyamura (1962) found that b values change from 0.40 to 1.80 according to the geological age of the tectonic area. The b-value for any region can be computed using several methods such as linear Least Squares (LS) regression or by the Maximum Likelihood (ML) method. ML method is the most robust and widely accepted method in which b-value is calculated using the formula (Aki, 1965); b

1 log10  M   M min  m / 2  

(2)

where Mmin is the minimum magnitude or threshold magnitude or magnitude of completeness (MC) for the earthquakes, M is the mean magnitude and m is the magnitude resolution. Motivated by laboratory experiments (Scholz, 1968; Amitrano, 2003), theoretical studies (e.g., Main et al., 1992), and observations (Schorlemmer et al., 2005) showing b-values decreasing 7

with increasing stress, investigators have sought temporal and/or spatial b-value variations that correlate with earthquake occurrence. Two viewpoints prevail: in the first, time-varying b-values are associated with large earthquakes or moment rate changes (Imoto, 1991; Kebede and Kulhanek, 1994; Sahu and Saikia, 1994; Enescu and Ito, 2001; Cao and Gao, 2002; Ziv et al., 2003; Nuannin et al., 2005). In the second, b-values are found constant in time, but spatial variations are related to earthquake occurrence and/or likelihood (Abercrombie and Brune, 1994; Westerhaus et al., 2002; Schorlemmer et al., 2003; Wyss et al., 2004; Schorlemmer et al., 2004; Wyss and Stefansson, 2006). 3.2 Fractal (Correlation) Dimension DC The fractal dimension, the DC value, is estimated using the correlation dimension. The 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

Dwr  limlog(Cr ) / log r

(3)

r 0

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 C (r ) 

2 N (R  r) N ( N  1)

(4)

where N(R
C (r ) r ( D2 )

(5)

where DC is a fractal dimension, more strictly, the correlation dimension (Grassberger and Procaccia, 1983). Smith (1988) suggested that a large number of datasets are required for the accurate estimation of DC. The distance (r) between two events (θ1, ϕ1) and (θ2, ϕ2) is calculated by using a spherical triangle as given by Hirata (1989):

r  cos 1[cos1cos2  sin1sin2cos(1  2 )

(6)

where θ1 and θ2 are the latitudes and ϕ1 and ϕ2 are the longitudes of the event 1 and event 2, respectively. DC is estimated as the slope of log10C(r) versus log10r using LS method. The fractal dimension may be used as a quantitative measure of the degree of heterogeneity of seismic activity in fault systems of a region, and it is controlled by the heterogeneity of the stress field and the preexisting geological, mechanical or structural heterogeneity (Öncel et al., 1996). If the earthquakes become progressively more clustered, the value of DC decreases (Öncel and Wilson, 2002). b value and DC value change from region to region because the applied stress level is different in the regions. 4 Data and Source Zonation The instrumental database including between 1900 and 2011 is used in this study (Bayrak et al. 2009). The data was compiled from different sources and catalogs, which are TURKNET, International Seismological Centre (ISC), Incorporated Research Institutions for Seismology (IRIS) and The Scientific and Technological Research Council of Turkey (TUBITAK). The catalogs include different magnitude scales (mb-body wave magnitude, MS-surface wave magnitude, ML-local magnitude, MD-duration magnitude, and MW-moment magnitude), the origin time, epicenter and depth information of earthquakes. The earthquakes from 1900 to 1974 were

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obtained from the ISC and instrumental catalog of Boğaziçi University, Kandilli Observatory and Earthquake Research Institute (KOERI). Turkey earthquake catalog starting from 1974 until 2011 was taken from the KOERI. We used only shallow earthquakes (h<70 km) to evaluate b and DC values for Western Anatolia. The earthquake catalog contains a total of 62136 earthquakes with magnitude 2.0≤Ms≤7.7 for the period 1900-2011. An earthquake data set used in seismicity or earthquake hazard studies must certainly be homogeneous, in other words, it is necessary to use the same magnitude scale. However, the earthquake data obtained from different catalogs have been reported in different magnitude scales. So, all earthquakes must be defined in the same magnitude scale. Bayrak et al. (2009) developed some relationships between different magnitude scales (mb-body wave magnitude, MS-surface wave magnitude, ML-local magnitude, MD-duration magnitude, and MW-moment magnitude) in order to prepare a homogeneous earthquake catalog from different data sets. We prepared a homogeneous earthquake data catalog for MS magnitude using these relationships. Although the scale of MW usually is used in the seismic hazard studies, MS magnitude in this study was preferred. Hanks and Kanamori (1979) determined that MW is calculated quite similar to MS for a number of earthquakes with MS≤8.0. It is necessary to consider seismicity, tectonics, geology, paleoseismology, and other neotectonic properties in a region for an ideal characterization of seismogenic source zones. Several authors defined different seismogenic source zones to study seismic hazard of Turkey (e.g., Alptekin, 1978; Erdik et al., 1999; Kayabalı, 2002; Bayrak et al., 2005; Bayrak et al., 2009, Cisternas et al., 2004, Gok and Polat, 2012). Bayrak et al. (2009) used different 24 source regions considering the different previous zonation studies for modeling of earthquake hazard in Turkey and 9 seismic source zones in these 24 regions are related to WA. Bayrak and Bayrak (2012a)

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divided WA into 15 seismogenic zones (Figure 2). In this study, we used these regions showed in Figure 2 and listed in Table 1 to investigate temporal variations of b and DC values and the relation between these parameters. 5 Results 5.1 Temporal Variation of b-value The most important information provided by temporal variation of b-value determine the stress situation with respect to time. Before medium or large earthquakes b-value generally decreases because of stress condition (Kanamori, 1981). After the main shock, b-value increases since stress condition decreases. According to these situations, b-values in different regions on Western Anatolia are calculated in order to investigate temporal variation of b-value before and after a medium or large earthquakes. In order to calculate the temporal variation of b-value, Zmap Software (Wiemer, 2001) was used. Before medium or large earthquake occurred, b-value had decreased in the related regions showed in Figure 3a-3b and listed in Table 2. In order to determine the evolution in time of b and DC values, we used a moving-window technique. In the region 1, b-value decreases before Izmir-Sigacik earthquake (17.10.2005) with magnitude 6.3. After the main shock, b-value increases immediately. In the region 5, b-value decreases until 1975, because the catalog includes earthquakes with magnitude M>4 until 1975. After this time, earthquake stations build many places for the development of technology, and seismologists begin to record small earthquakes easily. A small decrease of b value was observed in the year 2008 because of an earthquake 30.09.2008 with magnitude 4.7. In the region 8 surrounding Büyük Menderes Graben, b-value decreases in 1996 and 2006. b-value decreases from 1995 to 1996. An earthquake occurred 02.04.1996 with magnitude 5.1 and after this earthquake b- value

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increase prominently. b-value declines from 2002 to 2006, Aydın earthquake with magnitude 4.5. An aftershock occurred with magnitude 4.1 after the 15 minutes from this earthquake. bvalue decreases from 1988 to 1990 in the region 10 surrounding Aegean Arc. Three earthquakes occurred successively on 01.13.1990 with magnitudes respectively 4.6, 4.4 and 4.2. These earthquakes caused a decrease of b-value in this region. 01.10.1995 Dinar earthquake (M=6.0) was one of the big earthquakes around Western Anatolia the last twenty years in region 13. As can be seen Figure 3b, b-value in this region decreases before this earthquake. Sultandagi Fault (region 14) is one of the big faults in Western Anatolia. An earthquake occurred 03.02.2002, and forty-four people died and six hundred people injured during this earthquake and we observed b-value was decreased before this earthquake. As well as earthquakes in other regions, b-value decreases before the earthquake and increases after the event. When b-value decreases or increases, any earthquake is not reported in the regions 2 and 15. 5.2 Spatial Variation of b-value Western Anatolia was divided into 0.50x0.50 grids earthquake catalog in order to calculate the spatial variation of b-value. b-value calculated at each grid using Zmap with the maximum likelihood method (Figure 4). If any grid includes less than thirty earthquakes, we did not calculate b-value. Studies have shown that low P-wave velocities associated with high b-values (Ogata et. al., 1991). Salah et. al., (2007) make the distribution of P-wave velocity in 2 km/s. depth using seismic tomography method. They used 4,470 earthquakes and generated 13,559 P and 13,182 S arrivals recorded by the eight seismic stations belonging to the Turkish National Telemetric Earthquake Network (TurkNet). To analyze the arrival time data, they used the tomographic 12

method of Zhao et al. (1992). This method is adaptable to a general velocity structure, which includes several complex-shaped velocity discontinuities and allows 3-D velocity variations everywhere in the model. Between Gediz and Kücük Menderes Graben, low b values in concordance with high P-wave velocities (Figure 4). We observed lower b-values around Burdur-Fethiye and Acigol fault zones, and these values related with higher P-wave velocities. Lower b-values and higher P-wave velocities around Rhodos were calculated. Furthermore, southeast of Gediz graben, lower b-values correspond to higher P-wave velocities. Also, Polat et. al. (2008) mapped b-values around Western Anatolia and they obtained lower values for Rhodos. They calculated highest values around Buyuk Menderes graben, Akhisar fault and Bergama-Zeytindagi fault and concordance with our b-values. This is a fact that there is a direct proportion between b-values and heat flow. Gürer et. al. (2001) mapped heat flow values on western Anatolia. Higher b-values observed BergamaZeytindagi fault zone with also higher heat flow values. In opposite, lower values of these terms defined in and around Dumlupinar fault zone (390N-300E). On the other hand, higher b-values are reported from areas of increased geological complexity (Lopez Casado et al., 1995), indicating the importance of the multifracture area. Increased material heterogeneity or crack density results in high b-values (Mogi, 1962). Faults of all sizes are surrounding this area and also western Anatolia has graben systems such as Büyük Menderes Graben and Gediz Graben. We observed higher b-values around these graben systems (Figure 4). Laboratory tests showed that an increase of thermal gradients caused an increase of b-value. (Warren and Latham, 1970). Dolmaz (2004) mapped thermal gradient for WA. Higher thermal gradients correspond to higher b-values around Beysehir Lake, whereas lower thermal gradients

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equal to lower b-values between Isparta-Antalya cities. Kutahya fault zone has higher stress condition the reason why these parameters are inverse. Lower b-values obtained around Sandıklı and Kumdanlı faults. Sandıklı and Kumdanlı faults are situated collision between Aegean and Anatolian plates (McClusky et al., 2003). As a result of this collision b-values on these faults is decreases. Furthermore, the bigger earthquakes occurred around these faults, so b-value was decreased. 5.3 3d Variation of b-value Estimation of 3D b-value mapping in the study area is performed by setting up 3D grids, having 0.5° × 0.5° × 2 km grid interval, selecting the nearest 200 events with 30 numbers in a minimum at each node using ZMAP software. The 3D b-value map, shown in Figure 5, is computed using the ML method. 3D b-value mapping is done along N–S vertical sections at 260 and 310 longitudes. Three horizontal slices are made at depths 20, 45 and 70 km. From 3D b-value mapping, it is observed that b-values in the study area vary from 0.45 to 1.55 following the pattern of high and low according to depth. The upper parts of graben systems exhibit higher bvalue than the lower parts of grabens. It suggests that the upper layer has high crustal heterogeneity and energy is being released due to frequent occurrences of earthquakes. The low b-value, smaller than 0.8, is observed around and under Aegean and Cyprus arcs which associated with the high-stress condition due to the subduction zone between Anatolian-African plates. 5.4 Temporal Variation of DC value DC values change with time and space relates to crust deformation and earthquake clustering (Aki, 1981; King, 1983; Turcotte, 1986). Before the occurred earthquake, DC value increases or

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decreases according to physical deformation and earthquake clustering in the region. DC with time different 15 source region in Western Anatolia was calculated (Figure 6a-6b). DC-b values were increased and decreased, respectively, before the earthquake occurred on 17.10.2005 with M=6.3 in the region 1 (Fig 6a-6b). Increasing DC value about 1983 in region 3 related to earthquake M=4.8 and also b value was decreasing before this earthquake. We observed this situation regions 5, 6, 7, 11 and 14 clearly. We observed that both DC and b values decreased before the earthquake occurred on 19.12.1990 with M=4.2 in the region 4. Also, this situation was observed in the regions 8, 9, 13 before the earthquakes associated to DC-b values directly proportional in these regions (Bayrak and Bayrak, 2012b). DC and b values decreased in the regions 10 and 12 related to Aegean arc before the earthquake occurred on 1990 and 2009. We think this situation is associated with higher stress condition and earthquake clustering. But, we couldn’t observe any earthquake where both b and DC values increased or decreased in the region 2 and 15 related to Akhisar and Beysehir, Kas faults respectively. Consequently, we clearly observed changing these parameters before an earthquake in Western Anatolia. 5.4 Spatial Variation of DC value The fractal dimension values between 1.65 and 2.55 were mapped (Figure 7). Lower DC values were obtained joining region between Aegean and Cyprus arcs, Burdur-Fethiye fault zone, Burdur Lake and North of Kucuk Menderes Graben. We calculated higher DC values Rodos Island, Cyprus, Izmir, Antalya and Sultandagi faults. Lower b values correspond to higher Dc values around Aegean arc. Bayrak and Bayrak (2012b) studied the relation between b-DC values around WA and they found negative relation these parameters.

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6 Conclusions We have analyzed earthquake catalog covering a period between 1900 to 2011 in order to study the temporal and spatial distribution of the fractal (correlation) dimension (DC) and G-R parameter (b) of the earthquake epicenters in 15 different seismogenic source regions in WA

We have employed the correlation integral method for estimation of DC and the ML method for the G-R relationship. The temporal variation of b and DC value were plotted using moving time windows with 30 events each region in WA. Time variation of b-values showed drops consistent with the occurrence of the

Also, 3D b-value was mapped for the study area is performed by setting up 3D grids, having 0.5° × 0.5° × 2 km grid interval, selecting the nearest 200 events with 30 numbers in a minimum at each node. We observed that b-value under the graben systems more and more decreases according to depth because material heterogeneity is more complex upper part of grabens.

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Acknowledgments Authors are grateful to Karadeniz Technical University (Turkey) for partially supporting this work (project number: 2010.112.007.4). The authors would like to express their gratitude to Editor of Journal of Asian Earth Sciences and two anonymous reviewers for their generous comments and thorough review of this manuscript, which has improved the quality significantly. The GMT software of Wessel and Smith (1998) was used to produce some of the figures. References Abercrombie, R.E., Brune, J.N., 1994. Evidence for a constant b-value above magnitude 0 in the southern San Andreas, San Jacinto and San Miguel fault zones, and at the Long Valley caldera, California. Geophysical Research Letters. 21, 1647– 1650. Aki, K., 1965. Maximum Likelihood Estimate of b in the Formula logN = a - bM and its Confidence Limits. Bulletin of the Earthquake Research Institute. Tokyo Univ. 43, 237239. Aki, K., 1981. A Probabilistic Synthesis of Precursory Phenomena, in Earthquake Prediction: An International Review, In: Simpson, D. W., Richards, P. G.,(Eds.), AGU, Washington, D.C., Maurice Ewing Set., 4, 566-574. Akman, A.Ü., Tüfekci, K., 2004. Determination and characterisation of fault systems and geomorphological features by RS and GIS techniques in the WSW part of Turkey. Int. Soc. for Photogrammetry and Remote Sensing, XX th Congress, 12-23 July 2004, İstanbul.

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Figure Caption Figure 1. (a) Location of study area in Turkey (b) Main tectonics of western Anatolia and focal mechanism (Tan, 2008, Bayrak and Bayrak, 2012a). Blue rectangle indicates the study area. Abbreviations: AGF – Acıgöl Fault, AKF – Akhisar Fault, BFZ – Burdur Fault Zone, BGF – Beyşehir Gölü Fault, BMG – Büyük Menderes Graben, BZFZ – Bergama- Zeytindağı Fault Zone, DG – Dinar Graben, EFZ – Eskişehir Fault Zone, FFZ – Fethiye Fault Zone, GÇF – Gölhisar-Çameli Fault, GDF – Gediz-Dumlupınar Fault, GG – Gediz Graben, İDF – İnönüDodurga Fault, KF – Kumdanlı Fault, KFZ – Kütahya Fault Zone, KMF – Karova-Milas Fault, KMG – Küçük Menderes Graben, KSF – Kas Fault, MYF – Muğla-Yatağan Fault, OFZ – Orhanlı Fault Zone, SDF – Sultandağı Fault, SF – Sandıklı Fault, SFZ – Simav Fault Zone

Figure 2. Epicenter distribution of earthquakes with M≥4.0 for instrumental period and 15 different seismogenic zones in Western Anatolia. Figure 3a. Temporal variations of b value regions 1-9 Figure 3b. Temporal variations of b value regions 10-15 Figure 4. Spatial variations of b value on western Anatolia Figure 5. 3D view of b-value at study area. The mapping is performed in a 0.50 x 0.50 x 2 km grid (latitude, longitude and depth), Selecting the nearest 200 events in each node. The three horizontal slices are shown at depths of 20, 45 and 70 km. The high b-value anomalies are colored red. Figure 6a. Temporal variations of DC value regions 1-9 Figure 6b. Temporal variations of DC value regions 10-15 32

Figure 7. Spatial variation of DC value on Western Anatolia

Table Caption Table 1. The Gutenberg-Richter (a and b) and fractal dimension (DC) parameters and their standard deviations of 15 different seismogenic zones in Western Anatolia (Bayrak and Bayrak, 2012b). Table 2. The observed earthquakes using temporal variation of b-value

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Table 1. Region

Tectonics

M max

MC

a

b

b

1 2 3

Aliağa Fault Akhisar Fault Eskişehir, İnönüDodurga Fault zones GedizGraben Simav, Gediz-Dumlupınar Faults Kütahya Fault Zone Karova-Milas, MuğlaYatağan Faults Büyük Menderes Graben Dozkırı-Çardak, Sandıklı Faults Aegean Islands Aegean Arc Aegean Arc, Marmaris, Köyceğiz, Fethiye Faults Gölhisar-Çameli, Acıgöl, TatarlıKumdanlı Faults, Dinar Graben Sultandağı Fault Beyşehirgölü, Kaş Faults

6.60 6.60 6.40

2.6 2.1 2.5

5.7 6.2 4.8

0.82 1.02 0.88

5.90 6.20

2.6 2.7

5.6 5.7

5.30 6.50

1.9 2.7

6.80 6.30

2.5 2.5

4 5 6 7 8 9 10 11 12 13

14 15

DC

DC

0.01 0.01 0.04

2.18 1.94 1.94

0.05 0.04 0.04

0.96 0.94

0.03 0.02

2.03

0.04 0.03

5.7 6.2

0.97 1.00

0.02 0.02

5.6 5.1

0.83 0.84

0.01 0.02

2.00 2.03 2.02 2.17

0.06 0.01 0.04 0.04

7.70 7.10 7.10

4.0 3.8 3.8

5.6 5.5 5.4

0.75 0.79 0.71

0.04 0.06 0.03

1.93 2.18 2.07 2.21

6.90

2.8

5.3

0.86

0.02

1.91

0.04

7.00 6.80

2.3 3.3

5.2 5.6

0.85 0.85

0.02 0.04

1.99 2.01

0.05 0.03

34

0.03 0.06 0.04

Table 2. Region 1 3 4 5 6 7 8 9 10

11

12 13 14

Longitude Latitude Date 26.53 38.15 17.10.2005 29.28 40.12 15.11.1983 28.04 38.59 19.12.1990 29.87 38.99 30.09.2008 31.75 38.84 25.07.1995 28.29 36.99 17.04.2006 26.36 37.65 23.12.2009 26.64 37.78 02.04.1996 28.68 37.91 05.06.2006 28.69 37.91 05.06.2006 29.29 37.93 21.04.2000 27.10 36.16 13.01.1990 27.17 36.12 13.01.1990 27.19 36.00 13.01.1990 26.55 34.40 27.09.1985 26.52 34.64 22.05.1986 26.99 34.82 23.09.2007 27.21 36.78 12.04.1996 27.86 36.58 26.04.1996 28.39 35.09 19.06.2009 30.05 38.11 01.10.1995 31.25 38.58 03.02.2002

35

Depth 9 7 7 5 25 12 5 12 8 11 11 6 5 12 41 48 5 56 27 41 5 10

Magnitude 6.30 4.80 4.20 4.70 4.00 4.30 4.20 5.10 4.50 4.10 4.80 4.60 4.40 4.20 5.50 5.20 5.20 4.90 4.80 5.60 6.00 6.10

b-value 0.86 0.55 0.79 1.22 1.03 1.06 1.13 1.05 1.12 1.12 1.20 0.81 0.81 0.81 1.10 1.10 0.94 0.97 0.97 0.99 0.76 0.90

(a)

(b)

Figure 1.

36

Figure 2.

37

Figure 3a.

38

Figure 3b.

Figure 4.

39

Figure 5.

40

Figure 6a.

41

Figure 6b.

Figure 7.

42

Graphical abstract

43

44

Highlights  We investigated the spatial and temporal variations of Gutenberg-Richter parameter (b) and fractal (correlation) dimension (DC). 

We interpreted the results in terms of seismicity, tectonic and seismotectonic properties in Western Anatolia.



The temporal variations of b and DC parameters were investigated for 15 different source zones in Western Anatolia.



We mapped 3d variations of b-value in Western Anatolia, for the first time.

45