Attenuation Characteristics of Central Asia

Date: 4/25/2019

Time: 06:00 PM

Room: Grand Ballroom

This study aims to determine the quality factor of P-waves Q_P, S-waves Q_S, and coda waves Q_C, in central Asia. We collected and compiled a database composed of 361 broadband seismograms from 186 local earthquakes recorded by 25 stations located in Afghanistan, Tajikistan, Uzbekistan, and Kazakhstan. These events have magnitudes ranging from 3 to 5.5 and hypocentral distance less than 200 km. Coda Q has been inferred for different coda window length of 20, 30, 40, and 50 sec using the single backscattering method. The coda Q values increase by increasing the coda window length indicating that the lower part of lithosphere is more homogenous than the upper part. For a coda window length of 40 sec, we obtained Q_C = 294 f ^0.586 and Q_C = 288 f ^0.598 for the vertical and horizontal directions, respectively, in the frequency range of 1 to 20 Hz. Our results show relatively low Q₀ values and strong frequency dependence behavior for coda and body waves in central Asia. Active regions often show strong frequency dependence of coda and body waves and the region under study follows a similar trend. Using the multiple-station coda normalization, we determined Q_P = 158 f ^0.706 and Q_S = 152 f ^0.856, in the frequency range of 1 to 20 Hz. Using the multiple-scattering interpretation of coda Q, intrinsic absorption and scattering attenuation have been separated. The intrinsic absorption is found to be very close to the coda attenuation and it dominates over the scattering attenuation particularly at high frequencies. Results from this study imply the presence of high degree of small-scale heterogeneities in the Earth’s crust and upper mantle beneath this region.

Presenting Author: Farhad Sedaghati

Authors