GNGTS 2014 - Atti del 33° Convegno Nazionale

GNGTS 2014 S essione 1.1 49 the May 20 event) fault segments to be approximately 70° and 45° respectively, associating the activated segments to the Mirandola system and to the intermediate thrust of the Ferrara system respectively. The authors also suggested that the observed discrepancy between the relocated afterschock alignments on the Mirandola thrust and the most of the fault-plane and geodetic solutions computed for the May 29 event indicating low dip angle of this thrust segment, could be explained by supposing that the May 29 event struck at the deeper, flatter portion of a fault segment of listric geometry, with most of the afterschocks occurring on the shallow, steeper part. Finally, the possible contribution of the early post-seismic deformation following the two mainshocks has not been assessed yet. Therefore, although the works that have been published so far have described the first-order geometrical and kinematic features of the thrust segments which were responsible for the two mainshocks, some additional complexities and discrepancies to this first-order scenario can be summarized as follows: 1) Some disagreement exists between the May 20 earthquake/fault association. Which segment of the Ferrara thrust system was activated during the May 20 mainshock? The intermediate or the innermost thrust? 2) May 29 earthquake/fault association. Most of the studies associate this event to the Mirandola thrust, however alternative hypothesis have attributed the May 29 mainshock to the westernmost and innermost thrust of the Ferrara system. 3) There is a discrepancy between fault planes solutions for the May 29 event and relocated aftershock alignments. Could this discrepancy explained assuming a listric geometry of the Mirandola thrust? Do the geodetic data require a listric geometry? 4) What is the contribution of the post-seismic deformation in the 2012 Ferrara seismic sequence? In this study, to address some of the open issues outline above, we present the preliminary results of the joint inversion of four different independent geodetic datasets (Fig. 1): about 67 km of high-precision levelling lines in the mainshocks epicentral area, including coseismic and early post-seismic deformation (first 12 months); repeated radar acquisitions covering the epicentral region are available for one RADARSAT-2 (RSAT2) interferogram calculated from two descending acquisitions on 30 April and 17 June 2012 pair and covering both the two Fig. 1 – Time line of coseismic and post-seismic intervals covered by the levelling lines, the InSAR interferograms and GPS displacements used in the present study. The red dashed lines represent the MW 5.9 May 20 and MW 5.8 May 29 events. The black dashed line indicates our nominally post-seismic starting epoch, starting 5 days after the May 29 mainschock.