Fault and Fluid Interaction during the 2012 Emilia (Northern Italy) Seismic Sequence

The triggering of large earthquakes by anthropic activities is a challenging issue in seis-
mology, invoked also for the M L 5.9 and 5.8 Emilia 2012 destructive earthquakes. The
interaction between the two earthquakes that propagated along adjacent thrusts is still
an open issue. In this study, we used waveform cross correlation and double-difference
(DD) location methods to precisely relocate the aftershock sequence and get insights into
fault geometry, structure, and rheology by means of DD seismic tomography. Accurate
relocations highlight a complex fault system with small-length fault segments coalescing
in the Mirandola and Ferrara thrusts. We observe a broad continuous high-V P = V S
anomaly at seismogenic depth (about 6.0 km) that suggests a possible hydraulic connec-
tion along the entire fault system. A close look at seismicity indicates a quasi-simultane-
ous activation of the entire thrust system, with the two mainshocks and large aftershocks
occurring within the high-V P = V S , high fluid pressure, and connecting volume.