A snapshot of the Northern Apennines (Italy) seismicity, merging catalogue and new seismic data

Abstract

In this paper we present the seismicity analysis of a small sector of the Northern Apennines in 27 terms of spatio-temporal distribution, merging data from the Italian seismic bulletin with new 28 data collected by temporal seismic networks. Our attention is focused on the region enclosed 29 between Toscana, Umbria, Marche and Emilia-Romagna. This area is mainly characterized by a 30 diffuse seismicity, partly clustered in small sequences (Mw < 4.7). Improved seismicity locations, 31 together with stress field analysis allows to characterize the manner of seismogenic stress release 32 in the area. Two regions of significantly different seismic release behavior could be 33 distinguished: (i) the inner/western part (Tuscan side) of the study area, where seismicity is 34 clustered at shallow depths (<18 km) and where strong earthquakes occurred in the past, (ii) the 35 outer(eastern) part (Marche side), where the seismicity is diffuse across all of the crustal volume, 36 reaching depths of down to 30 km. 37 Along the Apenninic chain, seismicity is nearly absent inside well defined zones. In our opinion, 38 these peculiarities of seismicity release could be related to the heterogeneity of crustal volume 39 and to the transition between Tyrrhenian and Adriatic domains.