Source parameters of microearthquakes at Phlegraean Fields (Southern Italy) volcanic area

Abstract

The seismic activity that occurred at the Pblegraean Fields (Southern Italy) volcanic area during a pronounced episode of ground uplift has been analysed. One hundred and eighty-one three component seismograms from a digital network operating in the period January—May 1984 were processed to obtain seismic moments, source radii and stress dropsfor32microearthquakes(0.7<ML< 3.2).Aninversemethodbasedonaleastsquaresfittingofdisplacement spectra with a theoretical model has been applied to infer the spectral parameters of P-radial and SH records. This method has the advantage of giving statistical errors on the spectral estimates. The computed seismic moments range between 0.5 x 1018 and 0.13 x 1021 dyne-cm. Stress drops are approximately constant, and do not clearly depend on seismic moments, which is in contrast with other reported data from microearthquake sequences. Small values of source radii (few tens of metres) are found.