A joint spatio-temporal investigation of stress drops and b-value of major seismicity in Italy

Fault stability is controlled by the balance between the accumulation of stress and the ability of the nearby crustal volumes to allocate it through their elastic properties avoiding accelerating strain localization. Even though the state of stress on fault is not accessible, it is possible to investigate different geophysical features which may provide useful information about the mechanical conditions of fault systems during the seismic cycle. Here, we perform a joint analysis of the stress drops of earthquakes and the b-value of seismicity in Italy. While the first parameter is a measure of the change in fault stress before and after the event, reflecting both mechanical conditions and frictional strength within the Earth's crust, the b-value is well-known to be somehow related to both fault roughness and accumulated stress. We analyse the most important seismic sequences in Italy during the last three decades, such as the Colfiorito 1997-1998, Molise 2002, L'Aquila 2009, Pollino 2012, Sannio-Matese 2013-2014, and Amatrice-Visso-Norcia 2016-2017 events. We show that synchronous changes of the b-value estimated using different approaches and stress drops are observed in both declustered and whole seismic activity. Our results show that a combined multiparametric approach to the analysis of seismicity may allow a deeper understanding of the physical processes at work in the brittle crust during the occurrence of seismic sequences.