Instrumental seismicity of the Amatrice earthquake epicentral area: a review

Abstract

This study presents a preliminary review of the instrumental seismicity of the Norcia-Amatrice area (central Italy) during the years preceding the on-going seismic sequence started on August 24th 2016 with a Mw 6.0 earthquake and occurred close to Accumoli village; a Mw 5.9 happened on October 26th, two months later, 3 km West of Visso and finally a Mw 6.5 on October 30th, 6 km North of Norcia, the largest earthquake recorded in Italy since the Mw 6.9 1980 Irpinia event. The clustering of earthquakes in time and space has been investigated by analysing seismic catalogs for the period 1981-2016, the CMT (Centroid Moment Tensor) catalogue and the TDMT (Time Domain Moment Tensor) solutions. The seismicity of this region is characterized by different types of activity: single events, minor sequences and swarms with hypocenters within the upper 15 km of the crust. A minor sequence on March 2007 (with maximum Mw 3.9 not followed by significant seismicity) affected the area East of Norcia close to the August 24th Mw 5.4 and close to the October 30th Mw 6.5. In the central area, near Accumoli, and in the southern sector close to Amatrice, minor seismic sequences occurred on February 2014 with a Ml 3.5 mainshock and on November 2013 with a Mw3.7 mainshock, respectively. We integrated hypocentral locations and fault plane solutions to give a first look at the main features of the instrumental seismicity compared to the present seismic sequence in order to relate seismicity patterns to the seismogenic structures of the target area.