Intrinsic and Scattering Attenuations in the Crust of the Racha Region, Georgia

Shengelia, Ia; Jorjiashvili, Nato; Godoladze, T.; Javakhishvili, Z.; Tumanova, N.

doi:10.1142/s1793431120500062

Cited by 11 publications

(7 citation statements)

References 41 publications

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“…Also, Q c is greater than Q s which is consistent with the model of Zeng [14], according to which values of Q i and Q sc should be such that Q c exceeds Q s . Similar results were obtained for the Racha region [46]. The knowledge of the relative amounts of scattering and intrinsic attenuation in the total attenuation is important because they characterize the tectonic of a region [3,[52][53][54][55].…”

Section: Resultssupporting

confidence: 78%

“…Frequency relationships of Q c vary from Q c = 62 ± 3 f 1 016±0 031 to Q c = 114 ± 7 f 0 865±0 053 for 20 s and 50 s lapse time windows, respectively. The time dependence of Q c values can be explained by several factors [43], but the main reason for the increase in Q c over time, especially for the single scattering model, is probably the change in attenuation with depth [7,[43][44][45][46]. According to Aki and Chouet [2], in the Q c method, when the source and the receiver are at the same points, coda waves sample different circular areas of radius V s t/2, where t = t coda + w/2 (t coda is the average starting time of coda waves, and w is the length of lapse time window), and V s is the average velocity of S waves (V s = 3 4 km/s).…”

Section: Resultsmentioning

confidence: 99%

“…Thus, we will be able to regionalize almost the entire territory of Georgia according to the Q parameter. ; line 2-Erzincan, Turkey [5]; line 3-Yunnan Province, China [57]; line 4-Racha, Georgia [46]; line 5-the Javakheti plateau, Georgia [51]; line 6-Arunachal Himalaya [8]; line 7-Tbilisi region (this study); line 8-the Bam region, Iran [58]; line 9-Northwest Caucasus [21]; line 10-Central Asia [59]; line 11-the Andaman Sea [7]. ; line 2-Umbria-Marche, Italy [41]; line 3-Racha, Georgia [46]; line 4-Arunachal Himalaya [8]; line 5-Tbilisi region (this study); line 6-W. Greece [60]; line 7-Andaman Sea [7]; line 8-Bam region, Iran [58]; line 9-Delhi, India [61]; line 10-Alborz region, Iran [62].…”

Section: Discussionmentioning

confidence: 99%

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Attenuation of Coda and Body Waves for Tbilisi and Surrounding Area, Georgia

Shengelia,

Jorjiashvili,

Godoladze

et al. 2024

International Journal of Geophysics

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The attenuation of high-frequency seismic waves was investigated in the crust beneath Tbilisi and the surrounding territory by analysing 225 local earthquakes that occurred from 2008 to 2020 and were recorded by eight seismic stations. The quality factors of coda waves QC and direct P and S waves, QP and QS, were estimated using the single backscattering model and the extended coda normalization method, respectively. The separation of intrinsic quality factors Qi from scattering quality factor QSC was fulfilled by Wennerberg’s method. Observed results show that all evaluated attenuation parameters are frequency-dependent in the frequency range of 1-32 Hz and increase with increasing frequency. Coda QC values increase also with increasing lapse time window from 20 s to 50 s and vary from 91±5 at 1.5 Hz to 1779±108 at 24 Hz, respectively. P waves attenuate slightly faster than S waves, and the ratio of QS/QP is more than unity and varies in a range of 1.5-1.8. The intrinsic and scattering quality factors are expressed by the following power laws: Qi=77±4f0.930±0.046 and QSC=219±6f0.924±0.050. The results show that Qi is close to QC, but QSC is larger than Qi, which means that intrinsic attenuation has a dominant role compared with the scattering effect. Our results were compared with those obtained in two other seismically active regions of Georgia, as well as with regions of the world. In general, the observed quality factors and their frequency-dependent relationships follow a similar trend, characterizing seismically active regions with complex tectonics. The calculated attenuation parameters characterize the entire earth’s crust under Tbilisi and the surrounding area. The results obtained will be useful in future seismological studies since the Q parameters are estimated for the first time for the given region.

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Section: Resultssupporting

confidence: 78%

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Attenuation of Coda and Body Waves for Tbilisi and Surrounding Area, Georgia

Shengelia,

Jorjiashvili,

Godoladze

et al. 2024

International Journal of Geophysics

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“…As was noted in [51], generally the lithosphere of the Caucasus is characterized by high attenuation. The Caucasus belongs to a relatively young tectonic structure and the attenuation of seismic waves in the lithosphere of the Caucasus is large; and, accordingly, the Q values are lower than in those regions where the age of folding is older.…”

Section: Resultsmentioning

confidence: 58%

“…Unfortunately, we can only compare Q S values, since Q P values for the Racha region have not been estimated until now. The Q S values are also low for Racha, they increase with increasing frequency and are expressed according to power-law as ð31 ± 2Þf 1:038±0:037 [51]. Thus, the attenuation parameters are similar for these two regions of Georgia, Q S values change at 1-24 Hz frequency band from 42 to 808 and 46 to 863 for Javakheti and Racha regions, respectively.…”

Section: Resultsmentioning

confidence: 87%

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

Shengelia

Jorjiashvili

Godoladze

et al. 2022

International Journal of Geophysics

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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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Qβ, Qc, Qi, Qs of the Gargano Promontory (Southern Italy)

et al. 2023

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We have provided the first estimate of scattering and intrinsic attenuation for the Gargano Promontory (Southern Italy) analyzing 190 local earthquakes with ML ranging from 1.0 to 2.8. To separate the intrinsic $${Q}_{i}$$ Q i and scattering $${Q}_{s}$$ Q s quality factors with the Wennerberg approach (1993), we have measured the direct S waves and coda quality factors ($${Q}_{\beta }$$ Q β , $${Q}_{c}$$ Q c ) in the same volume of crust. $${Q}_{\beta }$$ Q β parameter is derived with the coda normalization method (Aki 1980) and $${Q}_{c}$$ Q c factor is derived with the coda envelope decay method (Sato 1977). We selected the coda envelope by performing an automatic picking procedure from $${T}_{\mathrm{start}}=1.5{T}_{S}$$ T start = 1.5 T S up to 30 s after origin time (lapse time $${T}_{L}$$ T L ). All the obtained quality factors clearly increase with frequency. The $${Q}_{c}$$ Q c values correspond to those recently obtained for the area. The estimated $${Q}_{i}$$ Q i are comparable to the $${Q}_{c}$$ Q c at all frequencies and range between 100 and 1000. The $${Q}_{s}$$ Q s parameter shows higher values than $${Q}_{i}$$ Q i , except for 8 Hz, where the two estimates are closer. This implies a predominance of intrinsic attenuation over the scattering attenuation. Furthermore, the similarity between $${Q}_{i}$$ Q i and $${Q}_{c}$$ Q c allows us to interpret the high $${Q}_{c}$$ Q c anomaly previously found in the northern Gargano Promontory up to a depth of 24 km, as a volume of crust characterized by very low seismic dumping produced by conversion of seismic energy into heat. Moreover, most of the earthquake foci fall in high $${Q}_{i}$$ Q i areas, indicating lower level of anelastic dumping and a brittle behavior of rocks.

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Intrinsic and Scattering Attenuations in the Crust of the Racha Region, Georgia

Cited by 11 publications

References 41 publications

Attenuation of Coda and Body Waves for Tbilisi and Surrounding Area, Georgia

Attenuation of Coda and Body Waves for Tbilisi and Surrounding Area, Georgia

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

Qβ, Qc, Qi, Qs of the Gargano Promontory (Southern Italy)

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