Qc, Qp, Qs, Qi, and Qsc attenuation parameters in the southern part of Georgia

Georgia is located in the Caucasus between The black and the Caspian seas and is surrounded by the Greater and Lesser Caucasus. Among the seismic areas of Georgia, the volcanic upland of Javakheti situated in the south of Georgia is notable for its high level of seismicity where three large earthquakes with M6 occurred in the last century. The main goal of the study is to investigate the attenuation properties of the lithosphere in the region using a hundred and twenty local earthquakes in 2008-2020  recorded at five seismic stations equipped with broadband Guralp CMG40T and Trillium 40  seismometers. Earthquake magnitudes varied from 1.5 to 4.1; epicentral distances and depth were smaller than 60 km and 19 km, respectively. The quality factors of coda waves Q_cand direct P, S waves Q_p,and Qs have been estimated using the single back-scattering model and the extended coda normalization methods, respectively. Wennerberg’s approach has been used to estimate intrinsic Q_i and scattering Q_s attenuation parameters. The Q values were fitted to a  power-law, of form Q(f)= Q₀ (f)ⁿ, where Q₀ is the quality factor at 1Hz and n is the frequency relation parameter, which depends on the heterogeneity of the medium. The obtained values of Q_c, Q_p, Q_s, Q_i, andQ_sc show the frequency-dependent character in the frequency range of 1.5-24 Hz and are expressed as:

Q_c = (47.6±3.8)^{(1.034±0.048)},  Q_p = (17.4±2.3)𝑓^{(1.100±0.033)}, Q_s = (28.8±3.3)𝑓^{(1.048±0.039)}, 

Q_i = (62 ± 4) f ^{(0.969±0.052)},  Q_sc = (177 ± 6) f ^{(0.932±0.051)}

The calculated attenuation parameters characterize the entire earth's crust under the Javakheti plateau and the surrounding area. The observed Q_c and Q_i values are almost identical at different central frequencies and both of them are less than Q_sc. This means that the effect of intrinsic attenuation is dominated by scattering attenuation. Comparison of our results for similar lapse times to those obtained in other tectonic and seismic active regions show that the Q values and their frequency-dependent relationships are in an interval of values of tectonically active and highly heterogeneous regions. The results obtained will be useful for source parameter estimation, ground motion prediction, and hazard assessment of the study regions.