Foreshocks Detection for the 2012 Emilia (Italy) Earthquake Sequence: New Insights About Its Triggering

Abstract:

In May 2012 a sequence of earthquakes (Mw 6.0 and 5.8) occurred near the Cavone oil field, in northern Italy. The Po Plain region, where this earthquake sequence took place, is characterized by a low-to-moderate level of seismicity. The exploitation of the Cavone oil field started in 1980. In order to maintain the fluid pressure in the reservoir, since 1993, about 2.6 Mm3 of produced waste water has been re-injected at the bottom of the reservoir (at 3.35 km depth, Juanes et al., 2016; Astiz et al., 2014). The northern limit of the Cavone oil field is bounded by the major Mirandola fault, which belongs to a system of thrust blind faults at around 20 km from the extraction wells. Works as Juanes et al. (2016) suggest that the two main earthquakes of this sequence occurred on separate en echelon blind thrust faults. Several authors have indicated that the production and injection could have minor effects in the triggering of the main earthquake of the sequence.

In this study we revisit the Emilia earthquake sequence. First, we analyze the available continuous waveforms applying template matching techniques to expand the earthquake catalog. Then, we describe the spatio-temporal evolution of the foreshock and aftershock activity in order to shed light into the mechanism(s) controlling this sequence. To do that, we use the double-difference relocation algorithm, which allows to have a high-resolution image of the study fault structures. In this work, we contribute to the understanding of the Emilia earthquake sequence with new observables and by assessing how seismicity develops, in time and space, around the two largest shocks of the sequence.