GNGTS 2018 - 37° Convegno Nazionale

GNGTS 2018 S essione 1.2 223 hangingwall and the footwall blocks of the seismogenic faults identified, at depth, through the hypocentres distribution analysis. The Norcia earthquake activated the SW-dipping Mount Vettore fault system, characterized by extensional/transtensional kinematics and dissecting the heterogeneous clayey/marly to carbonatic sedimentary succession of the Umbria-Marche Apennines (Barchi et al. , 2012); the Mount Vettore fault system is ~18 km long and consists of a series of SW-dipping faults (34–75°; Galadini and Galli, 2003). Moreover, the uplifted footwall block is not significantly affected by seismicity, whereas the uplifted area in the hangingwall block is bounded by a well-developed cluster of seismicity nearby the town of Norcia. In order to constrain the geometry and location of the tectonic structures involved during the Norcia earthquake, we take into account the relocated hypocentres (Chiaraluce et al., 2017) with 0.1≤M w ≤ 6.5 that occurred between 24 August and 29 November 2016, recorded by the INGV seismometric network. Specifically, once projected the relocated hypocentres onto sections, we highlight three different geological structures: (i) a SW-dipping alignment parallel to the main fault system, characterized by principal faults striking N150°– 160° and dipping 45°–55°; (ii) an E-dipping low-angle normal fault cutting through the upper crust; the relocated earthquakes highlight a flat structure which is located at most between about 8 and 10 km of depth and can also reach greater depths (down to about 12 km). This low-angle structure is the lower bound of the whole normal fault system, which is confined within the first 8 km of the upper crust, and coincides also with the lower limit of seismicity, the decollement surface; (iii) ENE-dipping structures that are antithetic to the main fault. In this context, we focus on the analysis of the vertical displacements retrieved from DInSAR measurements. In particular, we use two interferometric pairs acquired by the ALOS- 2 system: the first one was acquired along the ascending orbits on 24 August and 2 November 2016, respectively (Tab. 1); the second one was acquired along the descending orbits on 31 August and 9 November 2016 (Tab. 1), respectively. By combining the radar line-of-sight (LOS) displacements retrieved from these interferometric pairs, we compute the Vertical and the E-W displacement maps of the coseismic ground deformations, respectively. In particular, the vertical displacements are subsequently used for our rock volumes analysis. The retrieved map displays four main patterns: (i) a major subsidence reaching its maximum value of about 98 cm near the epicentral zones nearby the town of Norcia; (ii) three smaller uplift zones, one lobe that affects the hangingwall block (reaching maximum values of about 14 cm), a second one that affects the footwall block (reaching maximum values of about 10 cm) and an elongated easternmost deformation pattern (nearly parallel to the main Apennines structures). Tab. 1 - Coseismic interferometric pair exploited for the DInSAR analysis. ALOS-2 data pairs involving both the 26 October Visso and the 30 October Norcia events. Sensor InSAR pair Orbit Wavelenght Perpendicular Track Look angle (cm) baseline (m) (deg) ALOS-2 24082016-02112016 ASC 24.2 99 197 36.6 ALOS-2 31082016-09112016 DESC 24.2 59 92 32.8 ALOS-2 24082016-06092017 ASC 24.2 99 197 36.6 ALOS-2 31082016-24052017 DESC 24.2 59 92 32.8 To better discriminate which are the actual zones affected by ground deformation, we use two other interferometric pairs acquired by the ALOS-2 satellite. Specifically, one pair was acquired along the ascending orbits on 24 August 2016 and 6 September 2017, respectively; the second pair was acquired along the descending orbits on 31 August 2016 and 24 May 2017, respectively (Tab. 1). The analysis of this second data pair allows us to show that the elongated easternmost deformation pattern located in the footwall block is not clearly visible