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Coda Wave Attenuation Characteristics for North Anatolian Open Geosci. 2017; 9:480–490 Research Article Fadime Sertcelik* and Mehmet Guleroglu Coda Wave Attenuation Characteristics for North Anatolian Fault Zone, Turkey https://doi.org/10.1515/geo-2017-0037 Keywords: Coda wave attenuation, Frequency dependent, Received Dec 07, 2016; accepted Aug 03, 2017 North Anatolian Fault Zone, Lapse time Abstract: North Anatolian Fault Zone, on which large earthquakes have occurred in the past, migrates regu- larly from east to west, and it is one of the most ac- 1 Introduction tive faults in the world. The purpose of this study is to estimate the coda wave quality factor (Qc) for each of Seismic attenuation express as the decrease in the energy the five sub regionsthat were determined according to that seismic waves propagate in the earth and it is similar the fault rupture of these large earthquakes and along to seismic velocities. The variance in attenuation charac- the fault. 978 records have been analyzed for 1.5, 3, 6, teristics on the crust is a function of depth and lateral tran- 9, 12 and 18 Hz frequencies by Single Backscattering sition. Generally, the change in attenuation in the earth is Method. Along the fault, the variations in the Qc with a bit greater than the change in velocity. The energy de- lapse time are determined via, Qc = (136±25)f(0.96±0.027), crease for a seismic wave is directly proportional to ampli- Qc = (208±22)f(0.85±0.02)Qc = (307±28)f(0.72±0.025) at 20, 30, tude, and inversely proportional to the square of the dis- 40 sec lapse times, respectively. The estimated average tance. If the decrease in energy is arisen from the lateral frequency-dependence quality factor for all lapse time reflection, fracture, and/or scattering, it is defines asthe are; Qc(f) = (189±26)f(0.86±0.02) for Karlıova-Tokat region; attenuation of scattering (Qs), and if it is due to its convert- Qc(f) = (216±19)f(0.76±0.018) for Tokat-Çorum region; Qc(f) ing to heat as the result of internal friction, then it could = (232±18)f(0.76±0.019) for Çorum-Adapazarı region; Qc(f) = be defined as intrinsic attenuation (Qi).The quality factor (280±28)f(0.79±0.021) for Adapazarı-Yalova region; Qc(f) = (Q) is a significant parameter that is used often in seis- (252±26)f(0.81±0.022) for Yalova- Gulf of Saros region. The mological studies such as seismic hazard, focus mecha- coda wave quality factor at all the lapse times and fre- nism solutions, calculation of magnitude and crust struc- quencies is Qc(f) = (206±15)f (0.85±0.012) in the study area. ture. There searchers use different techniques for deter- The most change of Qc with lapse time is determined at mining the attenuation of seismic waves. While these stud- Yalova-Saros region. The result may be related to hetero- ies are being carried out under various pressure and tem- geneity degree of rapidly decreases towards the deep crust perature conditions at laboratories, they are also able to like compared to the other sub region. Moreover, the high- be performed by using P, S or surface waves at site obser- est Qc is calculated between Adapazari – Yalova. It was vations [1, 20, 22, 23, 25, 30, 33]. The data obtained from interpreted as a result of seismic energy released by 1999 near or far field can be analyzed as per the scope ofthe Kocaeli Earthquake. Besides, it couldn’t be established a study, and even the process can be performed by the time causal relationship between the regional variation of Qc or frequency domain. In recent studies researches have with frequency and lapse time associated to migration of used single scattering and multiple scattering models as the big earthquakes. These results have been interpreted suggested by [2] the most [14, 17, 24, 39, 40]. These mod- as the attenuation mechanism is affected by both regional els, where coda waves are being used, reveals the char- heterogeneity and consist of a single or multi strands of the acteristics of scattering that exist at the medium where is fault structure. located between the source and station. There is a strong relation between Qc and lapse time and frequency depen- dency. As the lapse time increases, information being ob- tained from depths of the earth increases. Thus, in cases where it has transferred to a more homogenous medium *Corresponding Author: Fadime Sertcelik: Kocaeli University –than the heterogeneity at upper parts- as it is preceded Kocaeli, Turkey; Email: [email protected] towards the depths, an increase in Qc is being observed. Mehmet Guleroglu: Email: [email protected] Open Access. © 2017 F. Sertcelik and M. Guleroglu, published by De Gruyter Open. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License Characteristics for North Anatolian Fault Zone Ë 481 Figure 1: (a) The earthquakes and fault rupture that had occurred in the recent century at North Anatolian Fault Zone. b) List of the earth- quakes that have occurred in the study area. NAFZ North Anatolian Fault Zone, DSFZ Dead Sea Fault Zone, EAFZ East Anatolian Fault Zone, NEAFZ North East Anatolian Fault Zone, GB Aegean Graben system. The frequency dependency of Qc is an indicator forthe tec- a region in southern Germany. They calculated that the Q tonic complexity of the area. There have been attenuation is lower in the western NAFZ than in the eastern NAFZ for studies that carried out using various methods in some a distance ranging from 15 to 40 km. part of North Anatolian fault zone (NAFZ). [29] calculated The results of our study, investigating the attenuation that there are relatively low coda-Q values for 5 and 10Hz characteristic in detail of NAFZ have high tectonic activity at the Izmit - Sapanca and Iznik - Mekece fault segments level could provide a significant contributions. These are; in comparison with the north region of the fault zones. first, the crustal attenuation characteristichas been deter- [42] had found Qc values are to be very low at between 30 mined for the whole NAFZ area that is covering through and 200 at the Iznik - Mekece fault in the North Anatolian 12 provinces in which Istanbul is included. Second, five Fault Zone and the frequencies from 2 to 10 Hz when com- sub regions were determined by considering where the pared with the values that range between 70 and 300 in large earthquake fractures are located. Qc change down the surrounding region. The reason for this is scattering to a depth of average 100 km had been determined with due to concentrated heterogeneous medium and temporal varying lapse time for each located region. Finally, the het- increase of intrinsic attenuation related to the preparation erogeneity degree of lower crust and upper mantle along for a large earthquake. [22] investigated the crustal struc- NAFZ has been determined. ture beneath the western part of the North Anatolian fault zone. The low-velocity and high-attenuationpatterns cor- relatefor most part with the fracturing zones of the NAFZ. 2 Tectonic Setting and Seismic While low velocities have been observed beneath the main sedimentary basins (e.g., Adapazarı, Düzce, and Kuzuluk), Activity there have been high-velocity and low-attenuation pat- terns correlated with blocks presumed to be rigid found North Anatolian Fault Zone (NAFZ), which was first named in (Kocaeli, Armutlu, and Almacik blocks). [15] has calcu- by [18], and is morphologically distinct having seismically lated the attenuation of coda wave at Marmara region to active zones, which is among the most well-known faults beQc = 41f1.08 and Qs = 50f1.09 for 50 sec. lapse time. [5] in the world. The NAFZ is an active right-lateral strike-slip determined P wave attenuation of (Qp) along two portions fault with a length of 1200 km, and its width varies be- of the North Anatolian Fault Zone (NAFZ) in Turkey and in tween 100 m – 10 km. This fault constitutes as part of the 482 Ë F. Sertcelik and M. Guleroglu boundary in between Eurasia plate at north and Anatolian by 1.5 or 2 corresponding to the difference from theorigin plate at South. It extends from Karliova at east to Saros time of earthquake and the arrival time of the S wave.The Bay at west and is parallel to the shores of the Black Sea, reason for this is to prevent the coda wave from being af- and connects the East Anatolian compression area to the fected by the source [34]. Derived coda Q values show a Aegean – Cyprus arch [6–8] (Figure 1). clear dependence on frequency according to the relation- n In the recent century, the earthquakes that have oc- ship Q = Qof , where Q0 is the value of Qc at 1 Hz, and n rep- curred on NAFZ fault indicate that the earthquakes have resents the degree of frequency dependence of Qc. n value systematically migrated from east to west (Figure 1-a).The is effected from the heterogeneity of structure and alsoQo migration to west, was started in 1939 by the Erzincan has low values (<200) in the regions where the tectonic ac- earthquake that was Ms = 8.2, and concluded with the tivity is high. Izmit earthquake (Mw = 7.4) on August 17, 1999, and Duzce [32], in its Qc estimation was made by using coda earthquake (Mw = 7.2) on November 12, 1999. It has been wave, that referto the identification of a surface in the form emphasized by many studies that have been performed, of an ellipsoid.
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