Site response for the RSM seismic network and source parameters in the Central Apennines (Italy)

Thirty-three earthquakes which occurred in the Central Apennines (Italy) with M1 ranging from 2.4 to 3.7 have been spectrally analysed using digital recordings from twelve stations of the Rete Sismometrica Marchigiana (RSM) network. Data corrected for geometrical spreading and quality factor Q have been inverted by means of the Generalised Inversion Technique. Site responses have been compared with those obtained by H/V ratio. Site amplifications have been observed both at stations placed on Pleistocene sediments and at one station located at 1800 m altitude. Source parameters have been calculated by fitting the spectra with an automatic procedure adopting the omega (2) source model. The seismic moments range from 9.23 x 10(19) to 4.28 x 10(21) dyne-cm with an average M-0(S) to M-0(P) ratio of 1.13 +/- 0.38. The stress drops are generally low and they vary between 1.1 and 10.2 bar when estimated by using S source spectra, and between 0.5 and 7.1 bar when the P-source spectra are fitted. For the considered range of seismic moments we observe that the stress drop does not have significant dependence on event size.