Estimation of Coda Wave Attenuation in the East Anatolia Fault Zone, Turkey

Abstract

In this study, the attenuation of coda waves Q c (f) has been estimated for different lapse times and frequencies in the East Anatolia Fault Zone (EAFZ) in Turkey using a single back-scattering model of S-coda envelopes. The data include 255 earthquakes recorded by ten stations. The frequency-dependent Q c values are estimated at central frequencies of 1.5, 3, 6, 8, 12, and 18 Hz using 20-30-40 s lapse time windows. Along this fault zone, the frequency-dependent Q c obtained for all data and lapse time is Q c = 57.5f 0.82 . The entire study area is divided into six subregions according to the magnitude of the earthquakes and the location of the fault segments. The estimated average frequency-dependent relation for all lapse times are; Q c I ð Þ ¼ 34:3f 0:93 for Bingöl-KarliovaErzincan triple junction; Q c II ð Þ ¼ 56:3f 0:71 for Bingol-Lake Hazar segment; Q c III ð Þ ¼ 68:5f 0:75 for Lake Hazar-Sincik segment; Q c IV ð Þ ¼ 72:5f 0:78 Hazar-Sincik and Ç elikhan-Gölbaşı faults; Q c V ð Þ ¼ 59:7f 0:87 for Kahramanmaras triple junction and Q c VI ð Þ ¼ 67:4f 0:94 for Amanos Range and Karasu Basin. The lowest Q c is determined between Bingol and Malatya. The highest Q c value is along Amanos Range. In addition, Q c values are calculated for each regions at different lapse times. The average Q c value of the study region varies from 53 ± 11 at 1.5 Hz to 498 ± 41 at 18 Hz for 20 s lapse time window, as its variation is from 116 ± 11 at 1.5 Hz to 749 ± 75 at 18 Hz of central frequency for 40 s lapse time window. The increase of Q c with lapse times changes from one subregion to another along the fault zone. The rate of increment is significantly higher in Bingöl-Karliova-Erzincan triple junction than in the other subregions. This rapid increase of low Q c values in the junction reaches the general attenuation characteristics of the fault at 40 s lapse time. Finally, the low Q 0 and high n values can be attributed to the energy loss as a result of the heterogeneity and activity along the fault zone. The increase of Q c with frequency, lapse time may be related to heterogeneity decreases with depth. The rapid increase of Q c with depth in Bingöl-Karliova-Erzincan triple junction may be interpreted that the effect of the Northern Anatolian Fault Zone is effective in the upper crust is not so deep compared to EAFZ.

Spatial variation of coda wave attenuation using aftershocks of the Al Hoceima earthquake of 24 February, 2004, Morocco

“…Most studies show that the value of quality factor on 1 Hz, Q 0 , is less than 200 for tectonically and seismically active regions [8] such as Yunnan, China, Washington State, whereas larger have been observed for inactive or stable regions such as New England, South India and North Iberia (Figure 7). Thus our area is tectonically and seismically active regions such as Yunnan and China [3,8,9]. Low coda values for this area (Q 0 = 84.6) seem to be associated with tectonically and seismically active regions.…”

“…In the present study, the coda wave Q c is estimated following single backscattering model of Aki and Chouet [3,5,9,10,12]. Coda waves of local earthquakes can be considered as backscattered S and S waves generated by numerous heterogeneities present randomly but uniformly in the crust and upper mantle [3].…”

“…Coda waves of local earthquakes can be considered as backscattered S and S waves generated by numerous heterogeneities present randomly but uniformly in the crust and upper mantle [3]. From this model the coda amplitude represented as:…”

“…Attenuation, inverse of quality factor, is one of the most fundamental proprieties of seismic waves from which a lot of information about the earth can be deduced [3]. This parameter is an important factor for understanding the physical mechanism of seismic wave attenuation in relation to the composition and physical condition of the Earth's interior and it is also an essential parameter for the quantitative prediction of strong ground motion for the viewpoint of engineering seismology [4].…”

“…The single backscattering model given by Aki and Chouet [5], has been used in this study. This method is widely applied to studies in the crustal structures in different parts in the world [3,[6][7][8][9][10][11].…”