Detection of Spatial and Temporal Stress changes during the 2016 Central
Italy Seismic Sequence by monitoring the evolution of scaled energy
Abstract
We consider approximately 32,000 microearthquakes that occurred between
2005 and 2016 in central Italy to investigate the crustal strength
before and after the three largest earthquakes of the 2016 seismic
sequence (i.e., the Mw 6.2, 24 August 2016 Amatrice, the Mw 6.1, 26
October 2016 Visso, and the Mw 6.5, 30 October 2016 Norcia earthquakes).
We monitor the spatio-temporal deviations of the scaling between the
seismic moment, M0, and the radiated energy,
ES, with respect to a model calibrated for background
seismicity. These deviations, defined here as Energy Index (EI), allow
us to identify in the years following the Mw 6.1, 2009 L’Aquila
earthquake a progressive evolution of the dynamic properties of the
microearthquakes and the existence of high EI patches close to the
Amatrice earthquake hypocenter. We show the existence of a crustal
volume with high EI even before the Mw 6.5 Norcia earthquake. Our
results agree with the suggested hypothesis that the Norcia earthquake
nucleated at the boundary of a large patch that was highly stressed by
the two previous mainshocks of the sequence. Furthermore, we highlight
the mainshocks interaction both in terms of EI and of the mean loading
shear stress associated to microearthquakes occurring within the crustal
volumes comprising the mainshock hypocenters. Our study shows that the
dynamic characteristics of microearthquakes can be exploited as beacons
of stress change in the crust, and thus be exploited to monitor the
seismic hazard of a region and help to intercept the preparation phase
of large earthquakes.