Estimates of S-wave Q(f) in the rupture area of the mainshock and in the last-week foreshocks area preceding the L'Aquila 2009 (Mw6.1) earthquake sequence, Central Italy

Abstract

We used seismic records from the Central Italy seismic network to estimate the S-wave quality factor Q in the rupture area of the 6 April 2009 L'Aquila (Mw 6.1) mainshock and seven foreshocks with local magnitudes M_L 3.2–4.3 that occurred the week preceding the main event. We separated the attenuation along the source-station path by calculating individual nonparametric spectral attenuation functions for 21 frequencies between 0.20 and 25 Hz for each foreshock and the mainshock. Then, we estimated Q in the rupture zone using the ${\omega }^2$ source model as a reference. The rate of amplitude decay of the average source-station path attenuation functions is approximately the same for all the events except for two foreshocks located southwest of the main shock. We found that nearby the rupture-zone Q increases with frequency from 0.27 to 30.63 for the mainshock, and from 0.01 to 3.0 for the foreshocks. These low values of near-source Q obtained suggest the likely presence of fluids in the rupture areas of the foreshocks and the mainshock zone of the 2009 L'Aquila seismic sequence.