Attenuation in Southeastern Sicily (Italy) by applying different coda

Abstract

The attenuation in Southeastern Sicily has been investigated using 40 aftershocks of the December 13 1990, earthquake. The quality factor of coda waves (Qc) was estimated in the frequency range 1.5–24 Hz, applying three different methods in time and frequency domains. On the whole, a clear dependence of Qc on frequency was observed, according to the general law Q = Q0(f/f0) n . The frequency dependence relationships obtained from the analysis of coda waves at three lapse time windows (10, 20 and 30 seconds) show that, for all methods, Q0 (Qc at 1 Hz) significantly increases with lapse time. In particular, Q0 is approximately 20 at short lapse time (10 s) and increases to about 70 at longer lapse time (30 s). This is attributed to the fact that larger lapse times involve deeper parts of the crust and upper lithosphere which may be characterized by larger quality factors. Moreover, the value of the exponent n decreases with increasing coda lengths from about 1.3 to 0.9, suggesting a decrease in heterogeneity of the medium with depth. Finally, Qc-values here found are of the same order as those reported from other tectonic regions like the Anatolian Highlands or Southern Spain, while significantly higher than in the neighboring volcanic area of Mt. Etna.