Coseismic, aseismic and postseismic deformation, and source modeling of the May 2012 Emilia (Northern Italy) earthquakes

We present the results obtained with standard DInSAR and a time-series (SBAS) technique for the seismic sequence that affected the Emilia region (Northern Italy) in May-June 2012. We modeled the sources of the two greater seismic events occurred in the area, respectively on May 20th 2012, Ml 5.9, and May 29th, Ml 5.8, inverting surface displacement data derived from COSMO-SkyMed and Radarsat-1 SAR interferograms, integrated with GPS observations. Both sources were found to be best modeled by nearly E-W, South dipping thrust faults with a ramp-flat geometry. Using COSMO-SkyMed and Radarsat-1 interferograms covering different time periods, we additionally identified a positive displacement pattern of ~10 cm, occurring halfway the main displacement fields of the largest events of the sequence, which was not associated to any large aftershock and that we modeled adopting the geometries of the main thrust faults. The results suggest that this feature could be interpreted as an aseismic foreslip along the fault plane of the May 29th event, possibly caused by a reduction in frictional strength associated to local fluid overpressure caused by the May 20th mainshock. The Coulomb Failure Function analysis confirms an increasing load (6 bar) on the May 29th fault, caused by the May 20th event, in the same fault portion where the aseismic slip occurred. The stress was also increased by 2-3 bar on the two active faults closest to the activated thrusts, to the West and East of the epicentral area. We then focused on the post seismic phase, whose monitoring through the COSMO-SkyMed constellation is still ongoing; we combined ascending and descending passes, with a revisit time of 16 days. Results of post seismic deformation analysis will be presented at the meeting.