Regional Features of Seismic Wave Attenuation in the North Caucasus

Abstract—New generalized data on the attenuation of seismic waves in the lithosphere of the North Caucasus were obtained using the frequency-dependent quality factor of the medium Qs(f). Knowledge of the heterogeneities of the quality factor distribution as a characteristic of the environment in the region is necessary when carrying out seismic zoning work of varying degrees of detail. The information base for the study comprised digital records of 53 seismic stations of 800 local earthquakes with moderate magnitudes (1.8 ≤ M ≤ 5.5), evenly distributed throughout the North Caucasus. The study used the coda-wave envelope method in the single scattering model (CodaQ). For the territory of the North Caucasus and for seven individual zones, average analytical expressions of the frequency-dependent quality factor of the medium Qs(f) were calculated and maps of the distribution of quality values at frequencies of 1 and 4 Hz were compiled. It was revealed that the zones with the lowest quality factor correspond to tectonically heterogeneous regions characterized by the presence of strong fragmentation in the crust and an increased level of fluid saturation. The zones of the highest quality factor correspond to zones of lithospheric extension, where earthquakes with normal-fault focal mechanisms predominate.