GNGTS 2013 - Atti del 32° Convegno Nazionale

load on the May 29 th fault plane, following the first mainshock. Two seismic sourceswere obtained using the fault plane parameters provided byseveral published geological studies in this area (e.g. Boccaletti et al. , 2010; Picotti and Pazzaglia, 2008). This information is essential in this area, since, due to the symmetric shape of the deformation pattern and its small N-S component, the North/South dipping fault ambiguity could not be solved by SAR and GPS data inversion alone. The second example concerns the three largest events of the 2008 Baluchistan (western Pakistan) seismic sequence, namely two Mw 6.4 events only 11 hours apart and an Mw 5.7 event 40 days later. We used Synthetic Aperture Radar Differential Interferometry (DInSAR) (Figs. 2E, 2F and 2H) and Multi-Aperture Interferometry (MAI) (Fig. 2G) to constrain the sources of these events. Our InSAR surface displacement maps and subsequent modeling results suggest the sources of the two main earthquakes of the Baluchistan 2008 seismic sequence were two NW-SE oriented right-lateral strike-slip faults (Figs. 2I and 2J). The modeled fault planes are found to be almost vertical and quasi parallel to each other, forming an about 90° angle with an ENE-WSW oriented fault responsible for the largest aftershock; the latter is a vertical left- lateral strike slip fault located between the two main sources. Moreover, CFF analysis suggests that the second mainshock fault plane was not overloaded by the first mainshock in spite of the very brief lapse of time between the two events. On the contrary, the December aftershock fault plane was intensely loaded by the occurrence of the October mainshocks. These results are insightful when interpreted in the tectonic context of the Quetta syntaxis. In fact, the latter is placed in crucial junction between two blocks characterized by opposite relative motion, namely the northward motion of the Kirthar range and the southward motion of the Sulaiman Lobe. The former can be considered the right block of the left- lateral strike-slip Chaman fault system, whereas the latter is considered a transpressive zone in the northwestern part of the Indian subcontinent (Yadav et al. , 2012), with a southward extrusion accommodated by the SE verging thrust fault surrounding the lobe itself and the left-lateral Kingri fault (Rowlands, 1978). In this complex tectonic context, our quasi parallel mainshock fault planes are in good agreement with a right-lateral shear zone located in the Quetta syntaxis. Moreover, the CFF suggests the October 28 th and 29 th earthquakes were two independent mainshocks characterized by a similar magnitude, mechanism and geometry. Conversely, concerning the December 9 th aftershock, the stress increase along the fault plane due to the mainshocks suggests that it was likely triggered by the October earthquakes. Thus, at this scale, in the area included between the two mainshock fault planes, we can suppose a reorientation of the stress field due to the general right-lateral displacement of the blocks. Under this assumption, our observations, together with the modelled fault geometries, suggest that at a local scale this area could be affected by left-lateral shear zone, with a bookshelf type deformation, in a wider regional tectonic context of right-lateral shear zone, confirmed by our mainshock modelling. This test case is characterized by the almost total absence of geological data at surface and at depth, as well as of any coseismic ground evidences of surface faulting. Constraints for source modeling are provided only by the abundance of SAR measurements (three independent motion components could be measured for the main events) and from seismology. In particular, the MAI technique was crucial in solving the fault plane ambiguity determined by moment tensors. Our results and hypothesis would however have to be confirmed by a field geological survey and a more accurate seismological study of the seismic sequence, as well as of stress readjustments and reorientations analysis during the seismic sequence evolution. Ground deformation during the postseismic phase. The first postseismic deformation analysis we present concerns the well-known deformation following the Mw 6.3 L’Aquila earthquake occurred on 06/04/2009 (Lanari et al. , 2010; D’Agostino et al. , 2012). We used 25 COSMO-SkyMed SAR images (beam 09 asc.) to obtain a postseismic deformation time series and mean velocity map (spanning12/04/2009 to 13/10/2009) (Fig. 3A). 99 GNGTS 2013 S essione 1.1