The 2012 Emilia seismic sequence (Northern Italy): Imaging the thrust fault system by accurate aftershock location

摘要

Starting from late May 2012, the Emilia region (Northern Italy) was severely shaken by an intense seismicsequence, originated from a ML 5.9 earthquake on May 20th, at a hypocentral depth of 6.3 km, with thrusttypefocal mechanism. In the following days, the seismic rate remained high, counting 50 ML ≥ 2.0 earthquakesa day, on average. Seismicity spreads along a 30 km east–west elongated area, in the Po river alluvial plain, in thenearby of the cities Ferrara and Modena. Nine days after the first shock, another destructive thrust-type earthquake(ML 5.8) hit the area to the west, causing further damage and fatalities. Aftershocks following this seconddestructive event extended along the same east-westerly trend for further 20 km to the west, thus illuminatingan area of about 50 km in length, on thewhole. After the first shock struck, on May 20th, a dense network of temporaryseismic stations, in addition to the permanent ones, was deployed in the meizoseismal area, leading to asensible improvement of the earthquake monitoring capability there. A combined dataset, including threecomponentseismic waveforms recorded by both permanent and temporary stations, has been analyzed inorder to obtain an appropriate 1-D velocity model for earthquake location in the study area. Here we describethe main seismological characteristics of this seismic sequence and, relying on refined earthquakes location,we make inferences on the geometry of the thrust system responsible for the two strongest shocks.