In this paper we examine the seismicity of Montefeltro, an historical region of northern Apennines in central Italy. The analysis focuses on the seismic activity occurred in the period 2005-2017 to exploit the substantial improvement of the National Seismic Network (RSN) in the region. We collected P and S phases from 402 earthquakes for a total of about 7000 arrival times. Earthquakes were integrated with new pickings and relocated using the Hypoellipse code. The results show a sporadic, rather diffuse background seismicity marked by three small seismic sequences strongly clustered in time and space. The most important occurred in September-October 2005 (ML=3.2) and August-September 2006 (ML=3.7), in the neighbourhood of the towns of Macerata Feltria and Casteldelci, respectively. The spatio-temporal evolution of these main episodes highlights an energy release consistent with swarm-like activity. Another major feature of the seismicity pattern is represented by the occurrence of events even in the lower crust and in the upper mantle down to at least 50 km depth.

Published: 2021-03-25