An Evaluation of Earthquake Hazard Parameters in and Around Ağrı, Eastern Anatolia, Turkey

Eastern Anatolian Journal of Science Eastern Anatolian Journal of Science Volume I, Issue I, 2015, 01-09

An Evaluation of Earthquake Hazard Parameters in and around Ağrı, Eastern Anatolia, Turkey

YUSUF BAYRAK1, AYSE NUR ATMIŞ1, FATMA TEMELLİ1, HIWA MOHAMMADI2, ERDEM BAYRAK3, ŞEYDA YILMAZ3, TUĞBA TÜRKER3 1 Ağrı İbrahim Çeçen University, Ağrı, Turkey 2 Shiraz University, Department of Earth Sciences, Iran 3 Karadeniz Technical University, Department of Geophysics, Trabzon, Turkey

Abstract Fault, Balıklıgölü Fault Zone, Kağızman Fault Zone, The earthquake hazard parameters of a and b Doğubayazıt Fault Zone, Karayazı Fault and Tutak Fault of Gutenberg-Richter relationships, return periods, Zone. Since these faults produce some large earthquakes expected maximum magnitudes in the next 100 years and (04 April 1903 Malazgirt (M=6.3), 13 September 1924 probabilities for the earthquakes for certain magnitude Pasinler (M=6.8), 24 November 1976 Çaldıran (M=7.3) values are computed using the earthquakes occurred and 30 October 1983 Horasan–Narman (M=6.8) during between 1900 and 2014 years in and around Ağrı. The instrumental earthquake time period, it is very important to relation of LogN=4.73-0.68M is calculated for the studied reveal earthquake hazard and risk in the area (BOZKURT area. The mapping of b values show that the regions in 2001). the east and southeast of Ağrı, east of Horasan and around Many quantitative methods have been applied over Patnos where low b values are computed have high stress the years to estimate seismicity in various regions of the levels and capacity to generate large earthquakes in the world. Several local and regional seismic hazard studies future. It is found that earthquakes larger than 5.5 may (ASLAN 1972; BATH 1979; YARAR et al. 1980; ERDIK be occurred in the regions where b values lower than et al. 1999; KAYABALI and AKIN 2003; BAYRAK et al. 0.8 have been observed in the next 100 years. The return 2005; 2009) have been performed in order to estimate the periods for magnitudes between 5.0 and 7.3 are estimated seismic hazard in Turkey using the statistical processing of between 5 and 176 years in the studied area, respectively. instrumental earthquake data. The probabilities of an earthquake with M=6.0, 6.5 and The most popular method used is the frequency- 7.0 in the next 100 years are computed 99%, 86% and magnitude relationship of Gutenberg-Richter (G-R). 59%, respectively. The largest earthquake occurred in the A large number of studies on a and b parameters of G- studied area is 7.3 and its occurrence probability is 43% in R relationship have been presented since Gutenberg the next 100 years. The faults around Ağrı are seismically and Richter introduced their law about the earthquake active and have potential for an earthquake larger than 6.0. magnitudes distribution. The different methods such as Since the sediment basin of Ağrı is very young and alluvial least square (LS) or maximum likelihood estimation (MLE) layer is tick, there is very high hazard on the buildings and can be applied to compute these parameters which are human’s life in Ağrı. very important in earthquake hazards and risk studies. The Keywords: b values, return period, expexted maxium, different hazard parameters such as the mean return period magnitude, Ağrı, Eastern Anatolia. for an earthquake occurrence, the most probable maximum magnitude of earthquakes in a certain time interval and the probabilities for the large earthquakes occurrences during 1. Introduction certain times using the parameters of G-R relationships. o The region in and around Ağrı (42.0-44.2 E and 39.0- BAYRAK et al. (2015) applied this method to the different o 40.5 N) covers seismically tectonic features such as Ağrı regions of the East Anatolian Fault. Fault, Bulanık Fault, Çaldıran Fault, Ercis Fault, Horasan Aim of this study is to evaluate the earthquake hazard Fault, Çobandede Fault Zone, Iğdır Fault, Malazgirt in and around Ağrı in terms of different hazard parameters. For this purpose, the mean return period, expected Accepted date: 15.04.2015 maximum magnitude of earthquakes in the next 100 years Corresponding author: and the probabilities for the large earthquakes occurrences Yusuf Bayrak, PhD in the next 25, 50 and 100 years are computed from the Agri İbrahim Çeçen University, Ağrı, Turkey parameters of G-R relationships using MLE. E-mail: [email protected] 2. Data

The database used was compiled from different sources and catalogs such as Turkey National Telemetric Seismic Network (TURKNET), Incorporated Research Institutions for Seismology (IRIS), the International Seismological Centre (ISC) and The Scientific and Technological Research Council of Turkey (TUBITAK) and is provided in different

magnitude scales. The catalogs include different magnitudes 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. An earthquake data set used in seismicity or seismic hazard studies must certainly be homogenous, 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 Y. Bayrak et al. Vol. I, Issue I, 2015 scales. Therefore, all earthquakes must be defined in the same magnitude scale. BAYRAK et

2.al. Data (2009) developed some relationships among magnitude different scale. magnitude BAYRAK scales et al. (2009) (Mb body developed wave some

The database used was compiled from different sources relationships among different magnitude scales (Mb body magnitude, Ms surface wave magnitude, ML local magnitude, MD duration magnitude and MW and catalogs such as Turkey National Telemetric Seismic wave magnitude, Ms surface wave magnitude, ML local Networkmoment (TURKNET), magnitude) Incorporated in order Research to prepare Institutions a homogenous magnitude, earthquake MD duration catalog magnitude from different and MW d momentata for Seismology (IRIS), the International Seismological magnitude) in order to prepare a homogenous earthquake Centresets. (ISC) and The Scientific and Technological catalog from different data sets. Research Council of Turkey (TUBITAK) and is provided We prepared a homogenous earthquake data catalog in differentWe magnitude prepared scales. a homogenous The catalogs include earthquake for dataMs magnitude catalog using for relationships Ms magnitude and have usingconsidered different magnitudes scales (M body wave magnitude, M only instrumental part of the earthquake catalogue (1900- relationships and haveb considered only instrumentals part of the earthquake catalogue (1900- surface wave magnitude, ML local magnitude, MD duration 2014). Finally, the catalog includes 1569 earthquakes with magnitude and M moment magnitude), the origin time M ≥1.1. The graphs of magnitude-earthquake number and 2014). Finally,W the catalog includes 1569 earthquakess with Ms ≥1.1. The graphs of magnitude- epicenter and depth information of earthquakes. years-cumulative earthquake number are shown in Figure Anearthquake earthquake numberdata set used and in years seismicity-cumulative or seismic earthquake 1. The recorded number earthquake are shown numbers in Figure have increased 1. The after 1976 depending on installed seismograph stations in hazardrecorded studies earthquake must certainly numbers be homogenous, have increased in other after 1976 depending on installed seismograph words, it is necessary to use the same magnitude scale. the studied area. Also, a large amount of magnitude of However,stations the in earthquake the studied data area. obtained Also, from a large different amount recorded of magnitude earthquakes of arerecorded lower than earthquakes 4.0 and the are size of catalogs have been reported in different magnitude scales. nine earthquakes are larger than 6.0. Therefore,lower allthan earthquakes 4.0 and the must size be of defined nine earthquakes in the same are larger than 6.0.

Figure 1. The graphs of, a) Earthquake number versus magnitude and b) cumulative number versus time for earthquakes in and around Ağrı

3. Tectonics and Seismicity sinistral character paralleling to North and East Anatolian The neotectonic evolution of the eastern Anatolian fault zones are the dominant structural elements of the region has been dominated by the collision of the region. Some of these structures include Ağrı Fault (AF), Arabian plates with the Eurasian plate along the Bitlis- Bulanık Fault (BF), Çaldıran Fault (ÇF), Ercis Fault (EF), Zagros suture zone (Figure 2). The eastern Anatolian Horasan Fault (HF), Çobandede Fault Zone (ÇFZ), Iğdır contractional province including the eastern Anatolian Fault (IF), Malazgirt Fault (MF), Balıklıgölü Fault Zone high plateau and the Bitlis-Pötürge thrust zone consists of (BFZ), Kağızman Fault Zone (KFZ), Doğubayazıt Fault an amalgamation of fragments of oceanic and continental Zone (DFZ), Karayazı Fault (KYFZ) and Tutak Fault Zone crusts that squeezed and shortened between the Arabian (TFZ), in the studied area shown by rectangular area in and Eurasian plates. This collisional and contractional zone Figure 1. Many pull-apart basins have developed along is being accompanied by the tectonic escape of most of the these structures (e.g., Erzurum and Ağrı basins). Although Anatolian plate to the west by major strike-slip faulting on the conjugate strike-slip fault system dominate the active the right-lateral north Anatolian transform fault zone and tectonics of eastern Anatolia, the E–W trending basins of left-lateral east Anatolian transform fault zone which meet compressional origin form the most spectacular structures at Karlıova (ELITOK and DONMEZ 2011). of the region as they indicate the N–S convergence and Depending on a N–S compressional tectonic regime, shortening of the Anatolian plateau. Muş, Lake Van and intra-plate deformation is dominant in the eastern Pasinler basins form the best examples of ramp basins in Anatolian. Conjugate strike-slip faults of dextral and the region (BOZKURT 2001). Figure 1.The graphs of, a) Earthquake number versus magnitude and b) cumulative number versus time for earthquakes in and around Ağrı 3. Tectonics and Seismicity

The neotectonic evolution of the eastern Anatolian region has been dominated by the collision of the Arabian plates with the Eurasian plate along the Bitlis-Zagros suture zone (Figure 2). The eastern Anatolian contractional province including the eastern Anatolian high plateau and the Bitlis-Pötürge thrust zone consists of an amalgamation of fragments of oceanic and continental crusts that squeezed and shortened between the Arabian and Eurasian plates. This collisional and contractional zone is being accompanied by the tectonic escape of most of the Anatolian plate to the west by major strike-slip faulting on the right-lateral north Anatolian transform fault zone and left-lateral east Anatolian transform fault zone which meet at Karlıova (ELITOK and DONMEZ 2011). Vol. I, Issue I, 2015 An Evaluation of Earthquake Hazard Parameters in and Around Ağrı, Eastern Anatolia, Turkey

Depending on a N–S compressional tectonic regime, intra-plate deformation is dominant in the eastern Anatolian. Conjugate strike-slip faults of dextral and sinistral character paralleling to North and East Anatolian fault zones are the dominant structural elements of the region. Some of these structures include Ağrı Fault (AF), Bulanık Fault (BF), Çaldıran Fault (ÇF), Ercis Fault (EF), Horasan Fault (HF), Çobandede Fault Zone (ÇFZ), Iğdır Fault (IF), Malazgirt Fault (MF), Balıklıgölü Fault Zone (BFZ), Kağızman Fault Zone (KFZ), Doğubayazıt Fault Zone (DFZ), Karayazı Fault (KYFZ) and Tutak Fault Zone (TFZ), in the studied area shown by rectangular area in Figure 1. Many pull-apart basins have developed along these structures (e.g., Erzurum and Ağrı basins). Although the conjugate strike-slip fault system dominate the active tectonics of eastern Anatolia, the E–W trending basins of compressional origin form the most spectacular structures of the region as they indicate the N–S convergence and shortening of the Anatolian plateau. Muş, Lake Van and Pasinler basins form the best examples of ramp basins in the region (BOZKURT 2001).

Figure 2. The tectonics in andThe around epicenter Ağrı. The distribution rectangle shows of the earthquakes study area. Ağrı larger Fault (AF), than Bulanık M=3.0 Fault is (BF),shown Çaldıran in Figure Fault 3. The (ÇF), Ercis Fault (EF), Horasan Fault (HF), Çobandede Fault Zone (ÇFZ), Iğdır Fault (IF), Malazgirt Fault (MF), Balıklıgölü Fault Zone (BFZ), FigureKağızmanfaults 2.FaultThe in Zone tectonics the (KFZ), studied Doğubayazıt in areaand aroundare Fault seismically Zone, Ağrı. Karayazı The active Fault rectangle (KYFZ) and formandshows Tutak the theFault source study Zone (TFZ) forarea. many (BOZKURT, Ağrı earthquakes. Fault 2001). (AF),The Bulanık largest Fault earthquakes (BF), Çaldıran, listed in FaultTable (ÇF),1, occurred Ercis in Fault the region (EF), are Horasan 04 April Fault 1903 (HF), Malazgirt The epicenterÇobandede distribution Fault of Zone earthquakes (ÇFZ), larger Iğdır than Fault (IF),occurred Malazgirt in the region Fault are 04 (MF), April 1903Balıklıgölü Malazgirt Fault (M=6.3), Zone M=3.0 is shown(BFZ), in(M=6.3), Kağızman Figure 3.13 The September Fault faults Zone in the1924 (KFZ), studied Pasinler Doğubayazıt13 (M=6.8), September Fault 24 1924 N Zone,ovember Pasinler Karayazı (M=6.8), 1976 Çaldıran 24 Fault November (KYFZ) (M=7.3) 1976 and and 30 area are seismicallyTutakOctober Fault active Zoneand 1983 form (TFZ) Horasan the (BOZKURT,source–Narman for many 2001).(M=6.8) Çaldıran (BOZKURT (M=7.3) and 2001). 30 October 1983 Horasan–Narman earthquakes. The largest earthquakes, listed in Table 1, (M=6.8) (BOZKURT 2001).

Figure 3. The epicenter distribution of earthquakes occurred in around Ağrı. Figure 3.The epicenter distribution of earthquakes occurred in around Ağrı. Table 1 Y. Bayrak et al. Vol. I, Issue I, 2015 The large earhquakes occurred in and around Ağrı.

Table 1. The large earhquakes occurred in and around Ağrı. Date Magnitude (M ) Location Date MagnitudeS (M ) Location 28 04 1903 6.30 S Malazgirt (42.50oE, 39.10oN) o o 13 0928 1924 04 1903 6.80 6.30 Pasinler (42.00MalazgirtoE, 40.00 (42.50oN) E, 39.10 N) 01 0513 1935 09 1924 6.00 6.80 Kars-Digor (43.22PasinleroE, 40.09 (42.00oN)oE, 40.00oN) observationso agreeo with the dependence of the b-value on friction and/or mean stress. The 15 0401 1960 05 1935 6.00 6.00 Horasan-NarmanKars-Digor (42.00 E, 40.50(43.22N)oE, 40.09oN) observationsdistinctiono agreebetween witho these the two dependence factors remains of the bdifficult-value onbecause friction they and/or are correlated, mean stress. as friction The 24 1115 1976 04 1960 7.30 6.00 Çaldıran-MuradiyeHorasan-Narman observations(44.20 E, 39.10 (42.00 agreeN) o withE, 40.50 theo N) dependence of the b-value on friction and/or mean stress. The 30 10 1983 6.80 Horasan (42.18oE, 40.35oN) 24 11 1976 7.30 Çaldıran-Muradiyedistinctiondecreases between when (44.20 thethese confiningoE, two 39.10 factors oN)pressure remains increases difficult (G becauseOEBEL theyet al. are 2012). correlated, On the as other friction hand, distinction between these two factors remains difficult because they are correlated, as friction 30 10 1983 6.80 decreaseshighHorasan b whenvalues (42.18 the areoE, confining 40.35 reportedoN) pressure from areas increases of increased (GOEBEL geological et al. 2012). complexity On the (LotherOPEZ hand, et al. decreases when the confining pressure increases (GOEBEL et al. 2012). On the other hand, 1995), indicating the importance of a multifracture area. Increased material heterogeneity or highhigh b values b values are arereported reported from from areas areas of increased of increased geological geological complexity complexity (LOPEZ (LOPEZ et al.et al. 4. Methods crack density results in high b values (MOGI 1962). Thus, a low b value is related to a low 1995),1995), indicating indicating the importancethe importance of a of multifracture a multifracture area. area. Increased Increased material material heterogeneity heterogeneity or or 4. Methods material heterogeneity or crack density results in high b degree of heterogeneity, large stress and strain, large velocity of deformation and large faults The empirical relationship, known as G–R law, between valuescrackcrack density(MOGI density results1962). results inThus, high in ahigh blow values b b values value (M OGIis(M relatedOGI 1962). 1962). to Thus, a Thus, a low a lowb value b value is related is related to a tolow a low The empirical relationship, known as G–R law, between the frequencies of earthquake the frequencies of earthquake occurrences and magnitudes low(M degreeANAKOU of heterogeneity, and TSAPANOS large stress 2000). and strain, large degreedegree of heterogeneity, of heterogeneity, large large stress stress and andstrain, strain, large large velocity velocity of deformation of deformation and andlarge large faults faults canoccurrences be expressed and in magnitudes the following can formula: be expressed in the followingvelocity formula: of deformation and large faults (MANAKOU and TSAPANOS(MANAKOU(MANAKOU 2000). and andT SAPANOS TSAPANOS 2000). 2000). b values were first estimated by GUTENBERG and RICHTER (1944) for various (1) regionsb valuesb values of were the were world.first first estimated They estimated(1) suggested by GUTENBERG by that GUTENBERG b values and range and from RICHTER 0.45–1.50, (1944) while forMIYAMURA various RICHTERb (1944) values for were various first regions estimated of the by world. GUTENBERG They and RICHTER (1944) for various regions(1962) of the found world. that Theyb values suggested change that from b values 0.40 –range1.80 accordingfrom 0.45 – to1.50, the while geological MIYAMURA age of the wherewhere N Nis isthe the cumulative cumulative number number of ofearthquakes earthquakes with with a a magnitudesuggestedregions of thatM of and theb greater,world. values They rangea and suggested b from 0.45–1.50, that b values while range from 0.45–1.50, while MIYAMURA MIYAMURAtectonic area. (1962) Globa foundl seismicity that b has values been change studied fromby several authors, and it has been found that magnitude of M and greater, a and b are constants. b is (1962)(1962) found found that thatb values b values change change from from 0.40 0.40–1.80–1.80 according according to the to thegeological geological age age of the of the are constants. b is the slope of the frequency–magnitude distribution,0.40–1.80 and according a is the toactivity the geological level age of the tectonic the slope of the frequency–magnitude distribution, and tectonicb values area. varyGloba betweenl seismicity 1.0 has and been 1.6 studied (MOGI, by 1962),several 0.8authors,–1.2 (McNand it ALLYhas been 1989), found 0.6that–1.5 a isof theseismicity. activity G levelUTENBERG of seismicity. and RICHTER GUTENBERG (1944) and firstly area.estimatedtectonic Global the seismicity area. constants Globa has lknown seismicity been studiedas has by been several studied authors, by several authors, and it has been found that andb values(U it DIAShas been vary and found betweenMEZCUA that 1.0b values1997) and 1.6varyand (M 0.53betweenOGI,–1.19 1962),1.0 (B andAYRAK 0.8–1.2 et (McN al. 2002).ALLY The 1989), b value 0.6 for–1.5 any RICHTERseismicity (1944) parameters. firstly estimated The parameter the constants a exhibits known significant as variationsb values from varyregion between to region 1.0 as and 1.6 (MOGI, 1962), 0.8–1.2 (McNALLY 1989), 0.6–1.5 seismicity parameters. The parameter a exhibits significant 1.6 region (MOGI, can 1962), be compu 0.8–1.2ted using (McNALLY several 1989),methods 0.6–1.5 such as linear least squares regression or by (UDIAS(UDIAS and andMEZCUA MEZCUA 1997) 1997) and and0.53 0.53–1.19–1.19 (BAYRAK (BAYRAK et al. et 2002). al. 2002). The Theb value b value for anyfor any variationsit depends from on region the level to region of seismic as it depends activity, on the the periodlevel of observation(UDIAS and and MEZCUA the length 1997) of and the 0.53–1.19 (BAYRAK regionMLE can which be compu is the tedmost using robust several and widely methods accepted such as method linear inleast which squares the bregression value is calculated or by of consideredseismic activity, area theas wperiodell as ofthe observation size of earthquakes. and the length The b valueet al. regionfor 2002). a region can The be bnot compuvalue only forted reflects any using region several can methodsbe computed such as linear least squares regression or by usingusing several the formula methods (A KI such 1965); as linear least squares of the considered area as well as the size of earthquakes. MLEM whichLE which is the is mostthe most robust robust and andwidely widely accepted accepted method method in which in which the bthe value b value is calculated is calculated the relative proportion of the number of large and small earthquakesregression in or the by region,MLE which but is is also the most robust and widely The b value for a region not only reflects the relative using the formula (AKI 1965); proportionrelated to of the the stress number conditions of large overand small the region. earthquakes Many factorsaccepted canusing cause method the formulaperturbation in which (AKI the of1965); bthe value is calculated using the formula (AKI 1965); (2) in normalthe region, b value. but isOn also average, related the to bthe value stress is conditionsnear unity for most seismically active regions on over the region. Many factors can cause perturbation of (2) the Earth (e.g. FROHLICH and DAVIS 1993). In a tectonically active region, the b value is (2) (2) the normal b value. On average, the b value is near unity Where is the average magnitude, and is the minimum value of the magnitude fornormally most seismically close to 1.0 active but varies regions between on the 0.5 Earth and (e.g.1.5 (P ACHECO et al. 1992; WIEMER and WhereWherepresenting isis the the averagedata. average In magnitude, ordermagnitude, to evaluate and and M these isis parameters, the the minimum we usedvalue to of ZMAP the magnitude 6 software FROHLICH and DAVIS 1993). In a tectonically active Where is the average magnitude, andmin is the minimum value of the magnitude WYSS 1997). However, a detailed mapping of b value oftenminimum reveals value significant of the magnitude deviations. presenting the data. In region, the b value is normally close to 1.0 but varies presentingpackage the(WIEMER data. In 2001) order. to evaluate these parameters, we used to ZMAP 6 software betweenThe spatial 0.5 and variations 1.5 (PACHECO of b values et al.are 1992; related WIEMER to the distribution orderpresenting toof evaluatestress and the these data.strain parameters, In(M orderOGI towe evaluate used to theseZMAP parameters, 6 we used to ZMAP 6 software and WYSS 1997). However, a detailed mapping of b value softwarepackagepackage package(WIEMER (WIEMER (WIEMER 2001) 2001). 2001).. 1967; SCHOLZ 1968). In addition, some researchers link the b-valueThe with parameter the parameters at depends of on the seismicity of the area, on the time interval for which often reveals significant deviations. The spatial variations The parameter at depends on the seismicity of the area, of theb valuesrupture are process. related An to exam the distributionple is SCHORLEMMER of stress and et al. (2005), who showed that the b- on thewe The time have The parameterinterval reported parameter for at which events depends at depends we and haveon also the onreported seismicity onthe theseismicity events surface of and the of area area,the area, S on outlined thone timeth e bytime interval the interval epicenters. for whichfor which For strainvalue (MOGI is dependent 1967; SCHOLZon the faulting 1968). style. In addition, As pointed some out by AalsoMITRINO on the surface (2012), area in laboratoryS outlined by the epicenters. For researchers link the b-value with the parameters of the seismicitywe have reportedstudy purposes events usually and also at is on expressed the surface in one area S outlined by the epicenters. For experiments with brittle rocks, the b-value depends on the mechanicalseismicitywe have loading, study reported purposes which events is usually the and also at is onexpressed the surface in one area year S by outlined the equation: by the epicenters. For rupture process. An example is SCHORLEMMER et al. year by the equation: (2005),type ofwho faulting, showed the that confining the b-value pressure, is dependent or the roughnesson the ofseismicity theseismicity fault slidingstudy study purposes surfaces. purposes usually These usually at is at expressed is expressed in one in oneyear year by the by equation:the equation: (3) (3) faulting style. As pointed out by AMITRINO (2012), in laboratory experiments with brittle rocks, the b-value whereThe t isexpected the whole time time interval period for covered the occurrence by the data of set. an earthquake with a magnitude greater (3) than (3) depends on the mechanical loading, which is the type of where t is the whole time period covered by the data set. faulting, the confining pressure, or the roughness of the The expected time interval for the occurrence of an earthquakeor equal with to M a ismagnitude defined as greater the mean than return or equal periods to M isTm and is given by: fault sliding surfaces. These observations agree with the wherewhere t is thet is wholethe whole time time peri odperi coveredod covered by the by datathe data set. set. dependence of the b-value on friction and/or mean stress. defined as the mean return periodsT m and is given by: The distinction between these two factors remains difficult because they are correlated, as friction decreases when (4) (4) the confining pressure increases (GOEBEL et al. 2012). On the other hand, high b values are reported from areas This quantity is adopted as a measurement of seismicity. of increased geological complexity (LOPEZ et al. 1995), The Tmosthis quantityprobable maximum is adopted magnitude as a measurement of earthquakes of seismicity.in The most probable maximum indicating the importance of a multifracture area. Increased a time period of t years: magnitude of earthquakes in a time period of t years:

(5)

The probability Pt for an earthquake occurrence with magnitude ≥ M during the time span of t

years:

(6)

In this paper, we aimed to make a quantitative appraisal of earthquake hazard

parameters in and around Ağrı. Particularly the analysis of the expected time interval for the

occurrence of an earthquake, the most probable maximum magnitude of earthquakes in a

given time period and the probability of an earthquake occurrence supply information on the

earthquake hazard. We used a MS magnitude scale in these equations since our catalogue is

uniform of MS.

5. Discussion and Conclusions We used 1569 earthquakes occurred between 1900-2014 years in the region of 42.0- 44.2 oE and 39.0-40.5 oN in order to evaluate earthquake hazard parameters in and around Ağrı. For this purpose, a and b parameters of G-R relationships, return periods, expected maximum magnitudes in the next 100 years and probabilities for the earthquakes for certain magnitude values are computed.

In this study, b value is calculated using ZMAP 6 software (WIEMER 2001). In particular, the b value was obtained by MLE estimation, using Equation (2). An estimation of The expected time interval for the occurrence of an earthquake with a magnitude greater than

The expected time interval for the occurrence of an earthquake with a magnitude greater than or equal to M is defined as the mean return periods Tm and is given by:

or equal to M is defined as the mean return periods Tm and is given by: (4)

(4)

This quantity is adopted as a measurement of seismicity. The most probable maximum Tmagnitudehis quantity of earthquakes is adopted in as a atime measurement period of t years: of seismicity. The most probable maximum Vol. I, Issue I, 2015 An Evaluation of Earthquake Hazard Parameters in and Around Ağrı, magnitude of earthquakes in a time period of t Easternyears: Anatolia, Turkey (5) of G-R relationships, return periods, expected maximum (5) magnitudes in the next 100 years and probabilities for the The probability Pt for an earthquake occurrence with magnitude ≥ M during the time span(5) of t standard deviation (δb) in b value can beearthquakes obtained for using certain the magnitude equation values derived are computed. by AKI (1965) Theyears:The probabilityprobability PPt t forfor anan earthquake earthquake occurrence occurrence with with magnitude In ≥ thisM during study, theb valuetime span is calculated of t using ZMAP 6 magnitude ≥ M andduring modiﬁed the time spanby S ofHI t years:and BOLT (1982):software (WIEMER 2001). In particular, the b value was years: obtained by MLE estimation, using Equation (2). An (6) standard deviation ( δb) in b value (6) can be obtained using the equation derived by AKI (1965) estimation of standard deviation (δb) in b value can be obtainedand modiﬁed using theby S equationHI and BOLT derived (1982): by AKI (1965) and In thisIn paper, this we paper, aimed weto make aimed a quantitative to make appraisal a quantitative appraisal of earthquake hazard (6) (7) of earthquake hazard parameters in and around Ağrı. modi fied by SHI and BOLT (1982): ParticularlyparametersIn thisthe in analysis paper,and around we of the aimedAğrı expected. Particularly to make time athe interval quantitative analysis of the appraisal expected of time earthquake interval hazardfor the (7) (7) for the occurrencewhere, of an n is earthquake, the sample the size. most probable maximumparametersoccurrence magnitude in of and an around earthquake, of earthquakes Ağrı .the Particularly most in a probable given the analysis time maximum of the magnitude expected time of earthquakes interval for inthe a

where, n is the sample size. period and the probability of an earthquake occurrence where, n is the sample size. occurrencegiven time period of an earthquake,andThe the cut probability- off the magnitude most of probablean earthquake (M maximumc) for occurrence the magnitudestudied supply area of information earthquakesshown in on Figure in the a 3 was estimated to be supply information on the earthquake hazard. We used a The cut-off magnitude (Mc) for the studied area shown

MS magnitude scale in these equations since our catalogue in Figure 3 was estimated to be equal to 2.7 ± 018 with givenearthquake time periodequalhazard. and toWe the 2. used7 probability± a 0 18MS magnitudewit ofh an 90% earthquake scale goodness in theseoccurrence ofequations fit supply leveThe since lcut (Figureinformation-off our magnitude catalogue 4). on The the ( Mis ca) forand the b studied values area for shown this in Figure 3 was estimated to be is uniform of MS. 90% goodness of fit level (Figure 4). The a and b values forequal this sequence to 2.7 ± shown 018 wit inh Figure 90% goodness4 were estimated of fit leve to lbe (Figure 4). The a and b values for this earthquakeuniform of Mhazard.sequenceS. We shownused a M inS magnitude Figure 4 scale were in these estimated equations to since be equal our catalogue to 4.73 is± 0.22 and 0.68 ± 0.04, equalsequence to 4.73 shown ± 0.22 in and Figure 0.68 4 ± were 0.04, estimatedrespectively to with be equal to 4.73 ± 0.22 and 0.68 ± 0.04, 5. Discussionrespectively and Conclusions with 90% goodness of fit level. The b value is lower than the global mean value uniform of MS. 90% goodness of fit level. The b value is lower than the We 5. used Discussion 1569 earthquakes and Conclusions occurred between 1900- globalrespectively mean value with of90% 1.0, goodness which indicates of fit level. that The the b data value is lower than the global mean value of 1.0, which indicateso that the data consists of larger earthquakes and high differential crustal 2014 yearsWe in used the region 1569 earthquakes of 42.0-44.2 occurred E and 39.0-40.5 between 1900-consists2014of 1.0, years of which larger in theindicates earthquakes region that of andthe 42.0 dahigh- ta consistsdifferential of larger crustal earthquakes and high differential crustal o 5. Discussion and Conclusions N in order to evaluate earthquake hazard parameters in stress in the region (WIEMER and KATSUMATA 1999; o stress in theo region (WIEMER and KATSUMATAstress in the 1999; region WIEMER (WIEMER andand K WATSUMATAYSS 2002). 1999; WIEMER and WYSS 2002). and44.2 around WeE and Ağrı. used 39.0 For 1569-40.5 this earthquakes purpose,N in order a occurred andto evaluateb parameters between earthquake 1900-WIEMER2014 hazard years parameters and in WYSS the region in 2002). and of around 42.0- 44.2Ağrı. o E For and this 39.0 purpose,-40.5 o Na inand order b parameters to evaluate of earthquake G-R relationships, hazard parameters return periods, in and expected around Ağrı.maximum For thismagnitudes purpose, in a theand next b parameters 100 years and of Gprobabilities-R relationships, for the return earthquakes periods, for expected certain maximummagnitude magnitudesvalues are computed. in the next 100 years and probabilities for the earthquakes for certain magnitudeIn this values study, are bcomputed. value is calculated using ZMAP 6 software (WIEMER 2001). In

particular,In this the study,b value b wasvalue obtained is calculated by MLE using estimation, ZMAP using 6 software Equation (W (2).IEMER An estimation 2001). Inof particular, the b value was obtained by MLE estimation, using Equation (2). An estimation of

Figure 4.The relationship of Gutenberg- Richter for the earthquakes occurred in around Ağrı. Figure 4. The relationship of Gutenberg- Richter for the earthquakes occurred in around Ağrı. Figure 4.The relationship of Gutenberg- RichterSpatial for mapping the earthquakes of b values occurred provides detailedin around information about seismotectonic Spatial mappingAğrı. of b values provides detailed 1.0situation are found in in the the studied region areacovering. For TF this and purpose, KYFZ. data It is are projected onto a plane to visualize observed b values larger than 1.0 in the west, northwest and information about seismotectonic situation in the studied values of b as a function of space. The mapping of b values is performed in a 0.1° × 0.1° grid, area. For this purpose,Spatial data are projected mapping onto of a bplane val toues providessouthwest of detailed Ağrı. It reveals information that this regionabout is seismotectonicassociated visualize values of b as a function of space. The mapping withselecting highly theterogeneoushe nearest 50 andevents fractured in each rock node matrix and that 25 events of the minimum number. The situation in the studied area. For this purpose,may be associated data are with projected fluids or onto viscous a plane materials to with visualize of b values is performed in a 0.1° × 0.1° grid, selecting estimated b value varies from 0.4 to 1.55 as seen from Figure 5. The b values lower than 0.8 fluids into the fractured rock matrix (SINGH et al. 2012a, the nearest 50 events in each node and 25 events of the values of b as a function of space. The mappingb).are The related regions of bto values inthe the area east is with performedand high southeast-stress in of regionsa Ağrı,0.1° eastincluding× 0. of1° grid, IF, DBFZ, BFZ, ÇF, EF and HF. b minimum number. The estimated b value varies from 0.4 selecting the nearest 50 events in eachHorasan node and around25 events Patnos of are the related minimum to b values number. lower The to 1.55 as seen from Figure 5. The b values lower than 0.8 than 0.8. It can be concluded that these regions have high are related to theestimated area with bhigh-stress value varies regions from including 0.4 to 1.55stress as seenlevels fromand capacity Figure to 5 occur. The large b values earthquakes lower in thethan 0.8 IF, DBFZ, BFZ, ÇF, EF and HF. b values between 0.8 and future time. are related to the area with high-stress regions including IF, DBFZ, BFZ, ÇF, EF and HF. b values between 0.8 and 1.0 are found in the region covering TF and KYFZ. It is observed b values larger than 1.0 in the west, northwest and southwest of Ağrı. It reveals that this region is associated with highly heterogeneous and fractured rock matrix that may be associated with fluids or viscous materials with fluids into the fractured rock matrix (SINGH et al. 2012a, b). The regions in the east and southeast of Ağrı, east of Horasan and around Patnos are related to b values lower than 0.8. It can be concluded that these regions have high stress levels and Y. Bayrak et al. Vol. I, Issue I, 2015 capacity to occur large earthquakes in the future time.

Figure 5.Figure The spatial 5.The distribution spatial of distribution b values computed of b fromvalues Gutenberg-Richter computed from relationships Gutenberg for -theRichter earthquakes relationships occurred in around for the earthquakes occurred in around Ağrı.Ağrı.

Spatial mapping of M100 values which computed by 6.0 in this region in the next 100 years. The magnitudes Spatial mapping of M100 values which computed by Equation 5 is shown in Figure 6. Equation 5 is shown in Figure 6. M100 is the most probable of expected earthquakes in the region between Ağrı and maximumM magnitude100 is the mostof earthquakes probable inmaximum a time period magnitude of ofHorasan earthquakes are lower in thana time 5.0. periodThe results of next show 100 that there is M next 100 years. The mapping of 100 values is performed an earthquake hazard about 5.5 around Patnos. The results in a 0.1° years.× 0.1° gridThe interval. mapping The of computed M100 values values is changeperformed in a 0.1° × 0.1° grid interval. The computed show that the earthquakes larger than 5.5 may be occurred between 3.6 and 7.0 as shown in Figure 6. The values larger values change between 3.6 and 7.0 as shown inin Figthe ureregions 6. Theof the values east and larger southeast than of 6.0 Ağrı, are Horasan- than 6.0 are computed in the IF, DBFZ, ÇF, HF and ÇFZ which producearoundcomputed large Patnos earthquakesin the where IF, DBFZ, asb shownvalues ÇF, in lower FigureHF and 2. th Thean ÇFZ 0.8 which Pasinler have produce been and around observed large Patnosearthquakes (Figure where 5), bas values Itshown can lower bein than 0.8 have been observed (Figure 5), It can be concluded that earthquakeconcludedFigure hazard 2. level Thethat in earthquakethese the regions regions of hazard Doğubeyazıt-Iğdır, have highlevel stressin the levels region ands of capacity Doğubeyazıt to occur-Iğdır, large Horasan earthquakes-Pasinler in Horasan-Pasinler and Çaldıran-Muradiye is very high and these regions have high stress levels and capacity to occur there is theaand probability next Çaldıran 100 toyears.-Muradiye occur an earthquakeis very high larger and than there is largea probability earthquakes to inoccur the next an 100earthquake years. larger than 6.0 in this region in the next 100 years. The magnitudes of expected earthquakes in the region between Ağrı and Horasan are lower than 5.0. The results show that there is an earthquake hazard about 5.5 around Patnos. The results show that the earthquakes larger than 5.5 may be occurred in the regions of the east and southeast of Ağrı, Horasan-Pasinler and

Figure 6. The spatial distribution of M100 values (expected maximum earthquake in the next 100 years) computed from Gutenberg- Figure 6.The spatialRichter distribution relationships of M for100 the values earthquakes (expected occurred maximum in around Ağrı. earthq uake in the next 100 years) computed from Gutenberg-Richter relationships for the earthquakes occurred in around Ağrı.

Earthquake recurrence times (return periods, Tm) computed from equation 4 and the probability of occurrence computed from equation 6 using the parameters of G-R relationship for the earthquakes larger a certain magnitude value during a given time span are listed in Table 2. Also, earthquake hazard curves expressed in terms of the return period and probabilities of earthquakes are shown in Figures 7 and 8. The mean return periods estimated for the studied area change between 5 and 176 years for magnitudes of 5.0-7.3 as listed in Table 2 and shown in Figure 7. For example, an earthquake equal to 6.0 which could cause damage to buildings and lost human may be occurred every 23 years. This is very high seismic risk value and we can conclude that the studied area very dangerous. Earthquake hazard curves expressed by the probability expected for earthquakes with the maximum observed magnitudes and plotted for magnitudes (and during the time span of 25, 50 and 100) are shown in Figure 8. The probabilities of an earthquake with M=6.0, 6.5 and 7.0 in the next 100 years are 99%, 86% and 59%, respectively. The magnitude of the largest earthquake Vol. I, Issue I, 2015 An Evaluation of Earthquake Hazard Parameters in and Around Ağrı, Eastern Anatolia, Turkey

Earthquake recurrence times (return periods, Tm) Table 2. The large earhquake risk values for next 25, computed from equation 4 and the probability of occurrence 50 and 100 years. computed from equation 6 using the parameters of G-R Earthquake Risk (%) relationship for the earthquakes larger a certain magnitude Return Ms Years value during a given time span are listed in Table 2. Also, Period(Tm) earthquake hazard curves expressed in terms of the return 25 50 100 period and probabilities of earthquakes are shown in Figures 5.0 0.99 1.00 1.00 5 7 and 8. The mean return periods estimated for the studied 5.1 0.99 1.00 1.00 6 area change between 5 and 176 years for magnitudes of 5.2 0.98 1.00 1.00 7 5.0-7.3 as listed in Table 2 and shown in Figure 7. For 5.3 0.96 1.00 1.00 8 example, an earthquake equal to 6.0 which could cause 5.4 0.93 1.00 1.00 9 damage to buildings and lost human may be occurred every 5.5 0.9 0.99 1.00 11 23 years. This is very high seismic risk value and we can 5.6 0.86 0.98 1.00 13 conclude that the studied area very dangerous. Earthquake 5.7 0.82 0.97 1.00 15 hazard curves expressed by the probability expected for 5.8 0.77 0.95 1.00 17 earthquakes with the maximum observed magnitudes and 5.9 0.71 0.92 0.99 20 plotted for magnitudes (and during the time span of 25, 50 6.0 0.66 0.88 0.99 23 and 100) are shown in Figure 8. The probabilities of an 6.1 0.6 0.84 0.97 27 earthquake with M=6.0, 6.5 and 7.0 in the next 100 years 6.2 0.54 0.79 0.96 32 are 99%, 86% and 59%, respectively. The magnitude of 6.3 0.49 0.74 0.93 37 the largest earthquake occurred in the studied area is equal 6.4 0.44 0.68 0.9 44 to 7.3 and the probability of it in the next 100 years is 6.5 0.39 0.63 0.86 51 43%. 6.6 0.34 0.57 0.81 59 6.7 0.3 0.51 0.76 69 6.8 0.27 0.46 0.71 81 6.9 0.23 0.41 0.65 95 7.0 0.2 0.36 0.59 111 7.1 0.18 0.32 0.54 129 7.2 0.15 0.28 0.48 151 7.3 0.13 0.25 0.43 176

Figure7.Figure The 7. returnThe return periods periods ofof earthquakes earthquakes in around in around Ağrı. Ağrı.

Figure 8.The probabilities for earthquakes for next 25, 50 and 100 years in around Ağrı. There is not any risk to occur earthquake larger than 5.0 in the center of Ağrı according

to spatial distribution of b and M100 shown in Figures 6 and 7 in the next 100 years. But, Ağrı is surrounded by active faults and probability of earthquakes greater than 6.0 in these faults is

Figure7. The return periods of earthquakes in around Ağrı. Y. Bayrak et al. Vol. I, Issue I, 2015

FigureFigure 8. 8.TheThe probabilities probabilities for earthquakes for earthquakes for next 25, 50 for and next 100 years 25, in50 around and Ağrı.100 years in around Ağrı.

There is not any risk toThere occur earthquakeis not any larger risk tothan occur studiedearthquake area arelarger estimated than between5.0 in the 5 andcenter 176 of years Ağrı for according 5.0 in the center of Ağrı according to spatial distribution of magnitudes of 5.0-7.3. The probabilities of an earthquake to spatial distribution of b and M100 shown in Figures 6 and 7 in the next 100 years. But, Ağrı b and M100 shown in Figures 6 and 7 in the next 100 years. with M=6.0, 6.5 and 7.0 in the next 100 years are computed But, Ağrı is surroundedis surrounded by active faults by active and probability faults and probability99%, 86% andof earthquakes59%, respectively. greater The thanprobability 6.0 in of these the faults is of earthquakes greater than 6.0 in these faults is very largest earthquake occurred in the studied area is 43% in high. There is a liquefaction risk in Ağrı due to a young the next 100 years. The faults around Ağrı are seismically sediment basin and alluvial layer is tick. We can concluded active and have potential to an earthquake larger than 6.0. that there is very high hazard on the buildings and human’s Since the sediment basin of Ağrı is very young and alluvial life considering liquefaction associated with an earthquake layer is tick, there is very high hazard on the buildings and might occur and this alluvium layer grows up to ten times human’s life in Ağrı. the earthquake waves (SEMBLAT et al. 2005). Acknowledgements: The authors would like to express their sincere thanks to Prof. Dr. Ali Pınar and the reviewers for the suggestions made in order for the paper to be 6. Results improved. Also, the authors are grateful to Ağrı İbrahim The earthquake hazard parameters in and around Ağrı Çeçen University BAP (Turkey) for partially supporting was evaluated for time interval of 1900-2014 years. For this work (with project number: PDBMF.15.001). this purpose, a and b parameters of G-R relationships, return periods, expected maximum magnitudes in the REFERENCES next 100 years and probabilities for the earthquakes for certain magnitude values are computed. a and b values for AKI, K. (1965), Maximum likelihood estimate of b in the formula log N = a - bM and its confidence limits. Tokyo Univ. this time period were estimated to be equal to 4.73 and Bull. Earthq. Res. Inst. 43, 237–239. 0.68, respectively. This b value shows that that the data AMITRANO, D. (2012), Variability in the power-law distribution consists of larger earthquakes and high differential crustal of rupture events. How and why does b-value change? stress in the region. The regions in the east and southeast European Physical Journal Special Topics. 205, 199- of Ağrı, east of Horasan and around Patnos have high 215. stress levels and capacity to occur large earthquakes in ASLAN, E. (1972), Magnitude and time distributions of the future time according to the mapping of b values. It earthquakes in Turkey. Bull Int Inst Seismol Earthq Eng. is found that earthquakes larger than 5.5 may be occurred 7, 1–10. in the regions where b values lower than 0.8 have been BATH, M. (1979), Seismic risk in Turkey—a preliminary observed in the next 100 years. The return periods in the approach. Tectonophysics. 54, 9–16. Vol. I, Issue I, 2015 An Evaluation of Earthquake Hazard Parameters in and Around Ağrı, Eastern Anatolia, Turkey

BAYRAK,Y., YILMAZTURK, A., and OZTURK, S. (2005), some related problems in earthquakes. Bull Earthq Res Relationships between fundamental seismic hazard Inst Univ Tokyo. 40, 831–883. parameters for the different source regions in Turkey. Nat MOGI, K. (1967), Earthquakes and fractures, Tectonophysics. Hazards. 36, 445–462. 5, 35–55. BAYRAK, Y., OZTURK, S., CINAR, H., KALAFAT, MCNALLY, K.C. (1989), Earthquakes and seismicity. In: James D., TSAPANOS, T. M., KORAVOS, C.G., and LEVENTAKIS, G.A. (2009), Estimating earthquake DE (ed) The encyclopedia of solid earth geophysics. hazard parameters from instrumental data for different Springer, 308–315. regions in and around Turkey. Eng Geol. 105, 200–210. PACHECO, J., SCHOLZ, C., and SYKES, L. (1992), Changes BAYRAK, Y., OZTURK, S., and ERDURAN, A., (2002), in frequency–size relationship from small to large The relationships between maximum magnitudes and earthquakes. Nature. 355, 71–73. modal values for different regions of Turkey. 3rd balkan SCHOLZ, C.H. (1968), The Frequency–magnitude relation of geophysical congress and exibition. 8–4, 24–28 June, microfracturing in rock and its relation to earthquakes, Sofia, Bulgaria. Bull Seismol Soc Am. 58, 399–415. BAYRAK, E., YILMAZ, Ş., SOFTA, M., TURKER, T., and SCHORLEMMER, D., WIEMER, S., and WYSS, M. (2005), BAYRAK, Y. (2015), Earthquake hazard analysis for Variations in earthquake size distribution across different East Anatolian Fault Zone, Turkey, Nat. Hazards. 76, 1063-1077. stress regimes, Nature. 437, 539–542. BOZKURT, E. (2001), Neotectonics of Turkey – a synthesis. SEMBLAT, J.F, KAHAM, M., PARARA, E., BARD, P.Y., Geodinamica Acta. 14, 3-30. PITILAKIS, K., MAKRA, K. and RAPTAKIS, D. (2005), Seismic wave ampications: Basin Geometry vs soil ELITOK, O. and DOLMAZ, M.N. (2011), Tectonic Escape Mechanism in the Crustal Evolution of Eastern Anatolian layering, Soil Dynamics and Earthquake Engineering. 25 Region (Turkey), New Frontiers in Tectonic Research (7-10), 529-538. - At the Midst of Plate Convergence, Dr. Uri Schattner SHI, Y., and BOLT, B.A. (1982), The standard error of the (Ed.), ISBN: 978-953-307-594-5, InTech, Available magnitude-frequency b-value, Bull. Seismol. Soc. Am. from: http://www.intechopen.com/books/newfrontiers- 72, 1677 – 1687. in-tectonic-research-at-the-midst-of-plate-convergence/ SINGH, A.P., MISHRA, O.P., YADAV, R.B.S., and KUMAR, D. tectonic-escape-mechanism-in-the-crustalevolution-of- eastern-anatolian-region-turkey (2012a), A new insight into crustal heterogeneity beneath the 2001 Bhuj earthquake region of northwest India and ERDIK, M., ALPAY, B. Y., ONUR, T., SESETYAN, K., and its implications for rupture initiations, Journal of Asian BIRGOREN, G. (1999), Assesment of earthquake hazard Earth Sciences. 45, 31–42. in Turkey and neighboring regions. Ann Geophys. 42, 1125–1138. SINGH, A.P., MISHRA, O.P, KUMAR, D., KUMAR, S., FROHLICH, C., and DAVIS, S.C. (1993), Teleseismic b values; and YADAV, R.B.S. (2012b), Spatial variation of the or, much ado about 1.0. J Geophys Res. 98, 631–644. aftershock activity across the Kachchh Rift Basin and its seismotectonic implications, Journal of Earth System GUTENBERG, R., RICHTER, C.F. (1944), Earthquake magnitude, intensity, energy and acceleration, Bull Sciences. 121 (2), 439–451. Seismol Soc Am. 32, 163–191. UDIAS, A., and MEZCUA, J. (1997), Fundamentos de Geofisica, GOEBEL, T.H.W., SCHORLEMMER, D., DRESEN, G., and QE 501. Alianza Editorial, Madrid. BECKER, T.W. (2012), Stress-driven in bv alues during WIEMER, S., and WYSS, M. (1997), Mapping the frequency– stick-slip on laboratoty fracture granite surfaces. Journal magnitude distribution in asperities: an improved of Geophysical Research. Doi:10.1029 technique to calculate recurrence times, J. Geophys Res. KAYABALI, K., AKIN, M. (2003), Seismic hazard map of 102, 15115–15128. Turkey using the deterministic approach. Eng GeoL. WIEMER, S., and KATSUMATA, K. (1999), Spatial variability 69,127–137. of seismicity parameters in aftershock zones. J. Geophys. LOPEZ, C.C., SANZ DE GALDANO, C., DELGADO, J., and Res. 13, 135-151. PEINADO, M.A. (1995), The b parameter in the Betic Cordillera, Rif and nearby sectors. Relations with the WIEMER, S. (2001), A software package to analyze seismicity: Tectonics of the region. Tectonophysics. 248, 277–292. ZMAP. Seismol Res Lett. 72, 373–382. MANAKOU, M.V., and TSAPANOS, T.M. (2000), Seismicity WIEMER, S., and WYSS, M. (2002), Mapping spatial variability and seismic hazard parameters evaluation in the island of the frequencymagnitude distribution of earthquakes, of Crete and the surrounding area inferred from mixed Adv. Geophys. 45, 259–302. files. Tectonophysics. 321, 157–178. YARAR, R., ERGUNAY, O., ERDIK, M., and GULKAN, P. MIYAMURA, S. (1962), Magnitude–frequency relations and its (1980), A preliminary probabilistic assessment of the bearing on geotectonics. Proc Jpn Acad. 38, 27–30. seismic hazard in Turkey. In: Proceedings of the 7th MOGI, K. (1962), Magnitude–frequency relationship for elastic World conference on earthquake Engineering, Istanbul. shocks accompanying fractures of various materials and 309–316.