Time Variability of crustal attenuation during the Amatrice-Visso-Norcia earthquake sequence in the Central Apennines (Italy)

Abstract

Over the last decade our work has been mostly about reducing uncertainties over spectral measurements in seismology (e.g. Malagnini and Munafò, 2018; Malagnini and Dreger, 2016; Munafò et al., 2016; Akinci et al., 2014). Here we measure time-domain peak values from narrow bandpass-filtered time histories and transform them into spectral estimates by using the theoretical results of Random Vibration Theory (Cartwright and Longuet-Higgins, 1956) and the Parseval Theorem. We develop a novel approach to quantify time domain fluctuations of highfrequency seismic attenuation and apply it to a massive data set of seismic waveforms from the Central Apennines in Italy, which includes recordings spanning the recent earthquake sequence of Amatrice-Visso-Norcia (2016-2017). Our observations show that the crustal seismic wave propagation in the region is strongly affected by transients triggered by the main events. The time varying attenuation is probably due to the associated migration of crustal fluids, in addition to seasonal oscillations related to precipitation-induced variations of crustal stresses. We also observe oscillation periods in the attenuation time series corresponding to solid Earth tides. Sensitivity to tides is stronger in the aftermath of the mainshocks, indicating an important role played by rock damage.