Was the Mirandola thrust really involved in the Emilia 2012 seismic sequence (northern Italy)? Implications on the likelihood of triggered seismicity effects

Abstract

We present the results of an interdisciplinary study aimed at defining the geometry of the fault segments activated by the Emilia 2012 thrust sequence (MW up to 6.1), which are located at the front of the Ferrara Arc (northern Italy) and partially overlap with an area undergoing hydrocarbon exploitation since 1980 (Cavone oil field). We relocate 40 well-recorded earthquakes with MW prevailingly ≥4.0 in the time interval from May 20 to June 12, 2012, plus an event that occurred in a nearby area on July 17, 2011 (MW 5.0). The geological and seismotectonic setting of the area is discussed, some interpretative geological sections across the hypocentral volumes are elaborated, and the shape of the identified individual seismogenic fault segments is schematically represented as depth contour lines. The resulting earthquake/fault association highlights a rather complex segmentation pattern, with four neighbouring sources involved, all belonging to the SSW-dipping Ferrara Thrust System. The two main events of the Emilia 2012 sequence did not activate the Mirandola thrust underlying the Cavone reservoir, although this thrust was illuminated by some subsidiary activity mainly concentrated close to the hydrocarbon field. The likelihood of triggered seismicity effects due to the extraction/ injection activities within the Cavone oil field are discussed.