Separation of scattering and intrinsic attenuation in southern Spain and western Anatolia (Turkey)

Abstract

We have obtained a separation of intrinsic and scattering attenuation in two tectonically active areas of the Mediterranean Basin, southern Spain and western Anatolia, using the Multiple‐Lapse Time Window Method. In southern Spain, Qs is predominant over Qi for frequencies lower than 4 Hz: between 4 and 8 Hz, results show similar scattering and intrinsic attenuation. For frequencies higher than 8 Hz, intrinsic attenuation is clearly dominant over scattering. Le−1 does not change uniformly with frequency: it increases until 8 Hz and decreases at frequencies greater than 8 Hz. The integrated energy curves of western Anatolia do not show regular change with distance. For the first energy window (0–15 s), there is a clear increase of the energy with distances between 0 and 80 km, and then a decrease after 80 km. The fit of the experimental data in the full hypocentral distance range is not good. We divided the experimental energy curves into two different segments, 0–80 and 80–170 km. In 0–80 km, Bo is close to 1 and the Le−1 values are low (0.004–0.013). In the second distance range (80–170 km) intrinsic attenuation is predominant over scattering. Qs−1 is more frequency‐dependent than Qi−1: f−l.47 against f−l.29. We observed that coda Q−1 is equal to the observed Qi−1 for intermediate frequencies, in both regions. However, Qc−1 is really similar to Qs−1 for short distances and is between Qi and Qs for long distances in southern Spain at low frequencies. Qc is similar to the observed Qt in both regions at high frequencies. The poor fit of the simulated curves with experimental data can be explained by introducing geometrical spreading values different to those used here. It is necessary to improve the model used by taking into account phenomena like non‐isotropic scattering, variation of attenuation with depth, the presence of surface waves or a geometrical spreading value different to the theoretical one used. Copyright © 1995, Wiley Blackwell. All rights reserved