Earthquake fault-plane solutions and patterns of seismicity within the Umbria Region, Italy

Abstract

In this paper we present a review of the seismotectonic features (an analysis of earthquake focal mechanisms and the distribution of seismicity) of the Northern Apennines, Umbria Region (Italy) in the area between Sansepolcro and Norcia. For this analysis, we used Centroid Moment Tensor (CMT) data for earthquakes with magnitude M>5.0 and data computed by implementing the standard CMT algorithm to compute Regional Centroid Moment Tensor (RCMT) estimates for moderate-magnitude earthquakes (4.5<M<5.5), integrating pre-existing datasets. We used first-motion polarities to obtain fault-plane solutions for small earthquakes (2.5<Md<4.5) recorded by the seismic network deployed by the Istituto Nazionale di Geofisica e Vulcanologia. We analyzed the main features of the seismicity and the present-day tectonic regime in order to relate the seismicity patterns to seismogenic structures beneath Central Italy. In particular, we discuss the important role of a major low-angle normal fault, the Altotiberina Fault, in controlling crustal seismicity in this region.