Seismicity and seismogenic structures in Central Italy: new insigths from the SLAM passive experiment

Abstract

We investigate the background seismicity of Central Italy in the area including southern Latium, Abruzzi and Molise (SLAM project). Within this region, the central Apenninic chain has been historically affected by many strong earthquakes, some of them very destructive such as the 1349 event (Mw ˜6.7) located at the border between southern Latium and western Molise, the 1654 event (Mw ˜6.4) in the southern Latium-Abruzzi area, and the 1805 Boiano earthquake in the northern Matese range (Mw 6.7). The last important seismic sequence occurred in May 1984 in the Comino Valley, southestern Latium (Mw 5.8). The recent activity is characterized by diffuse low-magnitude seismicity, punctuated by localised small sequences during 2009-2012. Our study focuses on the analysis of seismicity recorded in the period 2009-2013. We present earthquake locations and focal mechanism solutions obtained by standard procedures and an optimized regional 1D velocity model based on the Velest algorithm. The waveform data set was collected from the digital recordings of the permanent stations of the Italian national seismic network, the Abruzzi and Molise regional seismic networks, and from a dense seismic survey carried out in the region between November 2011 and May 2013. The temporary network consisted of 17 three-component seismic stations all equipped with Reftek RT130 digitizers and Lennartz 3D/5s sensors. The deployment of this array improved significantly the detection and location of background seismicity. We relocated more than 4300 events with magnitude ML ranging from about 0.5 to 4.2. Earthquakes distribution shows hypocentral depths concentrated within the upper crust, between 2 and 20 km of depth, and is mostly clustered along the Apenninic chain axis. The computed fault-plane solutions generally display normal fault mechanisms, confirming the extensional NE-SW processes active since Pleistocene in the study region.