Coda Wave Attenuation for Three Regions of Georgia (Sakartvelo) Using Local Earthquakes

Shengelia, Ia; Javakhishvili, Z.; Jorjiashvili, Nato

doi:10.1785/0120100326

“…There is a sufficient number of articles about the attenuation of seismic waves (body and surface waves) for the Caucasus (e.g., [18][19][20][21]), but only a few papers in which the attenuation properties of the lithosphere under the Javakheti plateau have been evaluated, and they were done mainly by means of analog records [22][23][24]. As it was noted [25], Georgia was the first country in the Caucasus where the attenuation properties of the earth's crust were investigated using the coda waves. In the early eighties of the last century, Q p and Q s were estimated by the coda normalization method on the basis of analog data for the entire territory of Georgia (but the attenuation was not estimated for the Javakheti area separately) in epicentral distances from 50 to 300 km [26].…”

Section: Introductionmentioning

confidence: 99%

Attenuation of P and S Waves in the Javakheti Plateau, Georgia (Sakartvelo)

Shengelia

¹

,

Jorjiashvili

²

,

Godoladze

³

et al. 2022

International Journal of Geophysics

1

3

0

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The frequency-dependent parameters of attenuation of P and S waves in one of the most seismically active regions, of the Javakheti plateau, have been estimated using digital data for the first time. We have analyzed and processed hundred and fifty local shallow earthquakes that occurred from 2006 to 2018 and were recorded by five seismic stations. The quality factors for P waves ( Q p ) and for S waves ( Q s ) were evaluated by means of the extended coda normalization method. The obtained Q p and Q s are strongly frequency dependent in the frequency range of 1.5 to 24 Hz, and increase with frequency according to the following power laws: Q P = 17.4 ± 2.3 f 1.100 ± 0.033 and Q S = 28.8 ± 3.3 f 1.048 ± 0.039 . The observed Q s / Q p ratio was found to be greater than unity over the entire frequency range, suggesting that scattering may play the main role in the attenuation of body waves on the Javakheti plateau. The frequency dependence of the S wave is very similar to the frequency dependence of the shear wave for another seismically active region of Georgia, the Racha area. A comparison of our results to those other regions of the world shows that among the seismically active areas, the Javakheti plateau is characterized by relatively low values of Q p and Q s , but they are more than volcanic regions such as Etna and Qeshm Island, Iran. The observed results characterize the entire earth’s crust in the study area and will be useful for source parameter estimation, ground motion prediction, and hazard assessment of the Javakheti plateau.

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“…Therefore, coda Q factor functions with a length of 40 as the coda window have been considered for consistency, if they were available. For tectonically active areas, low Q 0 values and high values of the frequency-dependent power η (Q 0 < 200, η > 0:7) have been reported (Aki and Chouet, 1975;Havskov et al, 1989;Woodgold, 1994;Hellweg et al, 1995;Giampiccolo et al, 2004;Rahimi and Hamzehloo, 2008;Padhy et al, 2011;Shengelia et al, 2011;Sertçelik, 2012;de Lorenzo et al, 2013;Ma'hood, 2014;Farrokhi et al, 2015). On the other hand, for tectonically inactive areas, high Q 0 values and low values of the frequency-dependent power η (Q 0 > 600, η < 0:4) have been acquired (Singh and Herrmann, 1983;Hasegawa, 1985;Pujades et al, 1990;Atkinson and Mereu, 1992;Atkinson, 2004).…”

Section: Comparison Of Results With Other Regionsmentioning

confidence: 95%

“…The coda quality factor represents the average attenuation property of an ellipsoidal volume with the source and receiver as its focus and depth as its height. Shengelia et al (2011) computed the penetration depth and covered area to be 56 km and 7071 km 2 for their proposed coda quality factor function (station ONI), in which the coda window length is 40 s. Ma'hood and Hamzehloo (2009) calculated the penetration depth and covered area equal to 65 km and 13;000 km 2 for their presented coda quality factor in which the coda window length is 40 s. Padhy et al (2011) estimated penetration depths to be 37.7, 172, and 150.8 km for different stations with a coda window length of 40 s. In the study of Kumar et al (2005), the authors estimated the penetration depth to be in the range of 77 to 188 km. Hence, we should mention that penetration depths and covered areas depend on the database used in the analysis, because the average focal depth and average hypocentral distance can vary based on records in the database.…”

Section: Area Covered By the Estimated Coda Quality Factors And Variamentioning

confidence: 99%

“…In addition to the reduction of the amplitude, attenuation distorts the phase part of a seismogram by delay, and this shift in the phase part causes velocity dispersion of seismic waves (Polatidis et al, 2003;Montaña and Margrave, 2004;Ruan, 2012). The attenuation derives from the geometrical spreading, scattering, and intrinsic absorption (Kumar et al, 2005;Padhy et al, 2011;Shengelia et al, 2011). A seismic wave initiates from a point source and it distributes over a spherical surface.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Estimation of the Coda‐Wave Attenuation and Geometrical Spreading in the New Madrid Seismic Zone

Sedaghati

¹

,

Pezeshk

²

2016

Bulletin of the Seismological Society of America

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Using the single backscattering method, coda quality factor functions through coda window lengths of 20, 30, 40, 50, and 60 s have been estimated for the New Madrid seismic zone (NMSZ). Furthermore, geometrical spreading functions for distances less than 60 km have been determined in this region at different center frequencies exploiting the coda normalization method. A total of 284 triaxial seismograms with good signal-to-noise ratios (SNR > 5) from broadband stations located in the NMSZ were used. The database consisted of records from 57 local earthquakes with moment magnitudes of 2.6-4.1, and hypocentral distances less than 200 km.Q-factor values were evaluated at five frequency bands with central frequencies of 1.5, 3, 6, 12, and 24 Hz. Vertical components were utilized to estimate vertical coda Q-factor values. Horizontal coda Q-factor values were determined using the average amount of the Q-factor values estimated from two orthogonal horizontal components. The coda Q-factor increases with increasing of the coda window length implying that with increasing the depth, the coda Q-factor increases. The intermediate values of the Q-factor and intermediate values of the frequency dependency indicate that the Earth's crust and upper mantle beneath the entire NMSZ is tectonically a moderate region with a moderate to relatively high degree of heterogeneities.The geometrical spreading factors of S-wave amplitudes are frequency dependent and determined to be −0:761, −0:991, −1:271, −1:182, and −1:066 for center frequencies of 1.5, 3, 6, 12, and 24 Hz, respectively, at hypocentral distances of 10-60 km. The geometrical spreading factors for lower frequencies are not recommended to be used due to the greater impact of the radiation pattern and directivity effect on low frequencies, as well as the greater sensitivity of band-pass-filtered seismograms of small earthquakes to the noise in low frequencies.

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“…Stress drop of this event is estimated to be 70 bars through the empirical formula presented in Riznichenko (1992). We use the regional intrinsic attenuation (Q) model in the form Q = 37f 1.089 as estimated by Shengelia et al (2011). As far as the kappa factor is concerned, for the rock and soil stations we used kappa values of 0.035 and 0.052, respectively.…”

Section: Simulation Of the 16 December 1990 Javakheti Earthquake (Mw mentioning

confidence: 99%

Hybrid-Empirical Ground Motion Estimations for Georgia

Tsereteli

¹

,

Askan

²

,

Hamzehloo

³

2016

Acta Geophys.

5

0

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Ground motion prediction equations are essential for several purposes ranging from seismic design and analysis to probabilistic seismic hazard assessment. In seismically active regions without sufficiently strong ground motion data to build empirical models, hybrid models become vital. Georgia does not have sufficiently strong ground motion data to build empirical models. In this study, we have applied the host-totarget method in two regions in Georgia with different source mechanisms. According to the tectonic regime of the target areas, two different regions are chosen as host regions. One of them is in Turkey with the dominant strike-slip source mechanism, while the other is in Iran with the prevalence of reverse-mechanism events. We performed stochastic finite-fault simulations in both host and target areas and employed the hybrid-empirical method as introduced in Campbell (2003). An initial set of hybrid empirical ground motion estimates is obtained for PGA and SA at selected periods for Georgia.

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Coda Wave Attenuation for Three Regions of Georgia (Sakartvelo) Using Local Earthquakes

Cited by 16 publications

References 26 publications

Attenuation of P and S Waves in the Javakheti Plateau, Georgia (Sakartvelo)

Attenuation of P and S Waves in the Javakheti Plateau, Georgia (Sakartvelo)

Estimation of the Coda‐Wave Attenuation and Geometrical Spreading in the New Madrid Seismic Zone

Hybrid-Empirical Ground Motion Estimations for Georgia

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