Seismicity of Garfagnana-Lunigiana (Tuscany, Italy) as recorded by a network of semi-broad-band instruments

Abstract

Eight seismic stations equipped with 5-second sensors have recently been installed in the Lunigiana-Garfagnana area to monitor activity in this sector of the Northern Apennines shaken by the 5.0Md earthquake of October 1995. The stations (RSLG network) represent an eastern branch of the RSNI (Regional Seismic network of Northwestern Italy) managed by Dipteris, Universita’ di Genova. The installation of this dense network allowed the operators to improve the magnitude detection level, providing information about the seismicity of the area down to magnitude 1.0. Several analyses have been carried out to evaluate the performance of the network and the reliability of the computed locations. It seems that the epicentral location for events occurring inside the network is already constrained using 8–10 P+S phases, but usage of more readings ensures reliability of depth and the reduction of location errors. Though not conclusive, as the network has only been fully operating for two years, a preliminary study carried out on a selected dataset of high-quality locations confirmed that the seismicity of the Garfagnana- Lunigiana is characterised by a low-to-medium magnitude level and it is subdivided into two bands, a superficial one about 30–35 km thick and the second below 50 km. This distribution, confirmed by other studies carried out in the past, reflects the complex structure of this area where two tectonic plates (European and Adriatic) meet.