SOME RESULTS OF STUDYING THE S-WAVE ATTENUATION FIELD IN THE CAUCASUS USING THE SHORT-PERIOD CODA METHOD
Schmidt Institute of Physics of the Earth, Russian Academy of Sciences
Journal: Problems of Engineering Seismology
Keywords: Caucasus, code waves, Q factor, S-wave attenuation field
Аnnotation: This work studies the characteristics of seismic coda waves attenuation in Caucasus. The short-period coda waves from about 500 earthquakes that occurred in Caucasus between 1989 and 2020 are analyzed. The three-component digital records of seismic events with M ≥ 4.0, recorded at epicentral distances of 120-600 kilometers, are used. S -wave attenuation was estimated from short-period coda envelopes at a frequency of ~1 Hz. The structural features of the S -wave attenuation field in the upper mantle of the Caucasus are similar to those for other seismoactive zones. The attenuation field is represented by blocks, which have weak attenuation and are subisometric in plan view, and strong attenuation zones. In the case of blocks, attenuation decreases in the direction from the boundaries to the central of these blocks ( Q factor is up to 300-1000). Sources of the strongest earthquakes in the region with M > 6.5 are confined to the boundaries of the blocks. A detailed structure of the attenuation field in the aftershock zones of the Dagestan 1970, Spitak 1988 and Racha 1991 earthquakes is considered. The obtained results agree with existing ideas about focal mechanisms of these earthquakes. The attenuation field structure corresponds to the velocity anomalies, the results of magnetotelluric and microseismic sounding, as well as thermal field anomalies.