Abstract

Seventy seismic events that occurred in southeastern Sicily with local magnitude ranging from 0.7 to 4.6 have been spectrally analyzed with digital recordings from nine stations. The events were recorded at hypocentral distances between 13 and 90 km and had a focal depth of less than 30 km. The coda-normalization method was used to estimate the frequency-dependent P-wave quality factor, QP(f), in the frequency range 1.5<f<28 Hz. It has been found that QP manifests a clear frequency dependence characterized by a power law function of QP=31f0.96. By taking into account the QS(f) by Giampiccolo et al. (2006), we found a ratio of QP/QS smaller than unity in the entire analyzed frequency range. Moreover, the same ratio takes the values between 0.63 and 0.83 and is comparable with the ratio VS/VP. Fourier displacement spectra were calculated for P and S waves and analyzed with respect to the source model of Brune (1970, 1971). These displacement spectra, corrected for near-surface attenuation parameter κ and the path attenuation, were then used to estimate source parameters. The seismic moments ranged from 1017 to 1022 dyne cm, the source dimensions from 59 to 737 m, and the static stress drop from 0.04 to 200 bars. The scaling of the seismic moment with the source dimension and with the static stress drop emphasizes a significant deviation from a constant stress drop scaling.

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