Monitoring long term seismic velocity changes in the Apennines region (ITALY)

Continuous noise-based monitoring of seismic velocity variations in the Earth’s crust could reveal crucial information about some of its dynamic processes and has a versatile applications. We investigate temporal velocity variations (dv/v) to probe the physical properties of seismogenic fault volumes, in the central Appennines. We aim to gain new insights into the physics of earthquake cycles along with transient tectonic deformations and shed new light into the depth dependent rheology of the crust. We perform velocity variation measurements on seismic noise autocorrelations over a period of 13 years for several lapse time coda windows, using the wavelet transform approach. A Markov chain Monte Carlo approach is finally used for the retrieval of dv/v time series, with daily resolution, at each of the Italian seismic station. Our results capture the evolution of dv/v prior and after the 2009 Mw 6.3 L'Aquila earthquake, the 2016 – 2017 central Italy earthquake sequence and during aseismic deformation episodes. We further observe signatures of several other processes as water level variation in the crust and loading (releases) related with climatic forcings. The detailed analysis of our high-temporal resolution dv/v time series, combined with geodetic and other seismological observables, permits to quantitatively assess the pre- and post-seismic processes, and the changes of crustal properties during episodes of aseismic deformation in shallow normal faults.