Body wave reconstruction from the cross-correlation of high frequency seismic noise in the Alto Tiberina Fault zone, Italy

We deployed two dense nodal arrays in the area comprising the Alto Tiberina Fault (ATF) system, Northern Apennines of Italy. This area is characterized by high geodetic strain-rates, with ~3 mm/yr of SW-NE extension partially accommodated by aseismic creep on the low angle ATF and partially by seismic swarm occurrences on the synthetic and antithetic faults in the hanging wall. High angle hanging wall faults play a role in seismogenic ruptures and during the occurrence of seismic swarms. The two almost linear arrays were roughly pointing towards a cement factory whose mills (while operating) could produce a seismic noise in the range [3 10] Hz. Thanks to this continuous (at intervals) source we could reconstruct the Green function of the medium from cross-correlations, and thus identify the arrival of the body waves, firstly in the nodal, but successively also in the permanent station recordings.

Measuring temporal changes of seismic velocities on body-waves reconstructed from noise cross-correlations between stations separated by tens of km should allow us to gain new insights into the evolution of the ATF and its surrounding faults at seismogenic depths, and to improve our understanding of the earthquakes preparatory phase.