GNGTS 2017 - 36° Convegno Nazionale

66 GNGTS 2017 S essione 1.1 From August 24 to October 25, seismicity mostly concentrated around the MST fault zone (Fig. 1a) defining a NNE–SSW-trending cluster parallel to the MST (Chiaraluce et al. , 2017), likely corresponding to the structural barrier (i.e., MST fault zone) at depth. The slip inversion analysis of the Ussita Mw 5.9 event indicates that the whole slip occurred in the hanging-wall block of the MST with a maximum rupture length of ca. 25-28 km, at a depth of about 2-4 km with respect to sea level (Fig. 1b). Surface rupture mapping carried out soon after the Ussita event and before the Norcia event showed the reactivation at surface of the northernmost segment of the VBF (Cupi fault segment: CF), with a maximum measured throw of 15-20 cm observed Fig. 1 - Cross-section parallel to the VBF-CVF-LF faults strike comparing rupture length and slip amount from the slip inversion with field observations: thick lines above each profile and thick dashed lines, where uncertain, indicate rupture length observed at surface; arrow indicates the site where the maximum surface throw was observed (surface rupture length along the Laga Fault are from Pucci et al. (2016). On the cross-section the locations of the main events, fault slips from the slip inversion (color-coded) transposed on the cross-section vertical plane), aftershocks distribution (grey dots are aftershocks in the period 24/08-25/10, purple dots are aftershocks in the period 26/10-29/10 and dark gray dots are aftershocks in the period 30/10-30/11), the main geological boundaries and the MST are represented. Note the good correspondence between the two dataset regarding ruptures extent and zones of maximum slip. The MST controlled the propagation and distribution of slip and seismicity, confining the ruptures of August 24 th and October 30 th . The October 30 th nucleated in correspondence of the MST and the associated slip involved the area remained almost unruptured after the first two main shocks. From Pizzi et al. (in press).