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 Sansepol- cro 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 Mo- ment 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-an- gle normal fault, the Altotiberina Fault, in controlling crustal seismicity in this region.
Highlights
The NE-verging Northern Apenninic Orogen is a typical fold and thrust belt
In this paper we study the seismicity patterns of 79 faultplane solutions determined for earthquakes that occurred in the Umbria Region of the Northern Apennines
The area investigated in this study is part of the central inner part of the Northern Apennines, which has been characterised by extensional tectonics since the Late Pliocene-Quaternary (Lavecchia et al, 1987; Barchi et al, 1998)
Summary
The NE-verging Northern Apenninic Orogen is a typical fold and thrust belt. It is dominated by concomitant extension and compression in two adjacent zones: the inner area of the belt, the present study area, and the outer margin of the belt, respectively (Elter et al, 1975; Lavecchia et al, 1987; Frepoli and Amato, 1997; Decandia et al, 1998). Subcrustal events in the Northern Apennines provide evidence of the presence of a subduction zone (Selvaggi and Amato, 1992; Amato et al, 1997; Chiarabba et al, 2005). This view is supported by tomographic images that depict a high-velocity body extending to 600 km depth (see Lucente et al, 1999 and references therein) that dips steeply toward the Tyrrhenian Sea. To determine a synoptic picture of the distribution and main features of regional-scale seismicity in this region, we analyzed different seismic sequences that occurred within the area. We integrate the results of previous studies with those of the present study, including data for moderate-magnitude events
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