Intrinsic and Scattering Seismic Attenuation in Southwestern Anatolia

摘要

The intrinsic dissipation and scattering attenuation in southwestern (SW) Anatolia, which is a tectonically active region, is studied using the coda waves. First the coda quality factor (Q c ) assuming single scattering is estimated from the slope of the coda-wave amplitude decay. Then the Multiple Lapse Time Window (MLTW) analysis is performed with a uniform earth model. Three non-overlapping temporal data windows are used to calculate the scattered seismic energy densities against the source-receiver distances, which, in turn, are used to calculate separate estimates of the intrinsic and scattering factors. In order to explore the frequency dependency, the observed seismograms are band pass-filtered at the center frequencies of 0.75, 1.5, 3.0, 6.0 and 12.0. The scattering attenuation (Q s −1) is found lower than the intrinsic attenuation (Q i −1) at all frequencies except at 0.75 Hz where the opposite is observed. Overall the intrinsic attenuation dominates over the scattering attenuation in the SW Anatolia region. The integrated energy curves obtained for the first energy window (i.e., 0–15 s) are somewhat irregular with distance while the second (i.e., 15–30 s) and third (i.e., 30–45 s) data windows exhibit more regular change with distance at most frequencies. The seismic albedo B 0 is determined as 0.61 at 0.75 Hz and 0.34 at 12.0 Hz while the total attenuation factor denoted by L e −1 changes in the range 0.034–0.017. For the source-station range 20–180 km considered the scattering attenuation is found strongly frequency dependent given by the power law Q s −1 = 0.010*f −1.508. The same relations for Q i −1, Q t −1 (total), Q c −1 and ${tilde{Q}}^{{- 1}}_{c}$ (expected) hold as Q i −1 = 0.0090*f −1.17, Q t −1 = 0.019*f −1.31, Q c −1 = 0.008*f −0.84 and ${tilde{Q}}_{c}^{{- 1}} = 0.014*f^{{- 0.87}},$ respectively. Compared to the other attenuation factors Q c −1 and ${tilde{Q}}^{{- 1}}_{c}$ are less dependent on the frequency.