Attenuation study in the Straits of Messina area (southern Italy)

Abstract

The attenuation of seismic waves is one of the basic physical parameters used in seismological studies and earthquake engineering, which is closely related to the seismicity and regional tectonic activity of a particular area. In this work, the seismic attenuation in the Straits of Messina, affected by several and strong historical earthquakes, was studied using waveforms recorded by a local seismic network composed of seven stations. We measured: the coda quality factor ( Q c) in the Single Scattering model hypothesis; the direct quality factor ( Q d) applying the Coda Normalization method for S-waves; and the intrinsic and scattering quality factor ( Q i and Q s) by the Multiple Lapse Time Window Analysis (MLTWA) method. Coda Q values were obtained using different lapse times (40, 60 and 80 s) for the frequency bands centred at 1.5, 3, 6 and 12 Hz. Our findings indicate that Q c increases with increasing lapse time and that Q c is frequency dependent. This behaviour is usually correlated to the degree of tectonic complexity and to the presence of heterogeneities at several scales. In fact, by using the Coda Normalization method we obtained low Q d values, as expected for a heterogeneous and active zone. Finally, by the MLTWA method we observe that the contribution of the scattering attenuation ( Q s − 1 ) prevails on the intrinsic absorption ( Q i − 1 ) until 3 Hz. Conversely, Q i − 1 and Q s − 1 seem to be of the same order in the higher frequency bands.