Ground Deformation and Source Geometry of the 30 October 2016 Mw 6.5 Norcia Earthquake (Central Italy) Investigated Through Seismological Data, DInSAR Measurements, and Numerical Modelling

Abstract

We investigate the Mw 6.5 Norcia (Central Italy) earthquake by exploiting seismological data, DInSAR measurements, and a numerical modelling approach. In particular, we first retrieve the vertical component (uplift and subsidence) of the displacements affecting the hangingwall and the footwall blocks of the seismogenic faults identified, at depth, through the hypocenters distribution analysis. To do this, we combine the DInSAR measurements obtained from coseismic SAR data pairs collected by the ALOS-2 sensor from ascending and descending orbits. The achieved vertical deformation map displays three main deformation patterns: (i) a major subsidence that reaches the maximum value of about 98 cm near the epicentral zones nearby the town of Norcia; (ii) two smaller uplift lobes that affect both the hangingwall (reaching maximum values of about 14 cm) and the footwall blocks (reaching maximum values of about 10 cm). Starting from this evidence, we compute the rock volumes affected by uplift and subsidence phenomena, highlighting that those involved by the retrieved subsidence are characterized by significantly higher deformation values than those affected by uplift (about 14 times). In order to provide a possible interpretation of this volumetric asymmetry, we extend our analysis by applying a 2D numerical modelling approach based on the finite element method, implemented in a structural-mechanic framework, and exploiting the available geological and seismological data, and the ground deformation measurements retrieved from the multi-orbit ALOS-2 DInSAR analysis. In this case, we consider two different scenarios: the first one based on a single SW-dipping fault, the latter on a main SW-dipping fault and an antithetic zone. In this context, the model characterized by the occurrence of an antithetic zone presents the retrieved best fit coseismic surface deformation pattern. This result allows us to interpret the subsidence and uplift phenomena caused by the Mw 6.5 Norcia earthquake as the result of the gravitational sliding of the hangingwall along the main fault plane and the frictional force acting in the opposite direction, consistently with the double couple fault plane mechanism.

Half‐Graben Rupture Geometry of the 30 October 2016 MW6.6 Mt. Vettore‐Mt. Bove Earthquake, Central Italy

“…Moreover, some modeling results show some persistent residuals in the Norcia area and in the southern part of the Castelluccio plain, where the geological study of Pierantoni et al () mapped antithetic structures on the western side of the Pian Grande basin (Figure ), while other authors suggested the presence of oblique faults bounding the basin (Pian Piccolo) to the south (Coltorti & Farabollini, ). For this reason, some authors (Cheloni et al, ; Chiaraluce et al, ; Pizzi et al, ; Scognamiglio et al, ; Valerio et al, ; Walters et al, ) suggested that the assumption that only a single planar fault slipped in the 30 October earthquake may not be exhaustive. In particular, Pizzi et al () and Chiarabba et al () issued that the oblique ramp of the low‐angle OAST may have played a role in differentiating the sources of the 24 August and 30 October events.…”

“…The possible secondary coseismic contribution of an oblique low‐angle fault to the 30 October rupture event has been tested in the geodetic modeling of Cheloni et al () who, nonetheless, defined this hypothesis as less probable than the coseismic activation of a major MVB antithetic fault plane. In addition, according to the 2D finite elements modeling of InSAR measurements of Valerio et al (), the presence of an antithetic fault zone is necessary to fully model the observed coseismic deformation pattern as depicted by InSAR measurements. On the contrary, Scognamiglio et al () modeled local SM and GPS data and proposed that a large amount of coseismic slip of the 30 October mainshock took place along a similar secondary low‐angle fault, oblique to the MVB fault system, and possibly associated to a deep portion of the NNE trending OAST ramp.…”

Fractal Study of the 1997–2017 Italian Seismic Sequences: A Joint Analysis of Seismological Data and DInSAR Measurements

“…We also emphasize that the coseismic deformation patterns present different characteristics for extensional and compressional seismic sequences (see Figures 2-7). Specifically, in the first case the ground deformation pattern is typically an image of the crustal block involvement during faulting processes [29]; accordingly, the deformation pattern retrieved on the Earth's surface is significantly spatially extended with respect to the main fault location (Figures 2, 3, 5, 6, 7 and 11a,b,d,e,f) [26,[28][29][30]. Conversely, in the second case the observed ground deformation pattern is strictly linked to the fault geometry; therefore, the measured ground deformation pattern is spatially less extended with respect to the main fault location (Figures 4 and 11c) [48].…”

“…During the last 20 years (since 1997), four seismic sequences with M w ≥ 5.5 mainshocks nucleated within different tectonic settings (i.e., extensional and compressional environments) along the Central and Northern Apennines chain, causing casualties and damage: the 1997 Colfiorito, the 2009 L'Aquila, the 2012 Emilia, and the most recent 2016-2017 Central Italy seismic sequences [25][26][27][28][29][30][31]. In this work, we study these four seismic sequences by exploiting the available seismological data and applying fractals theory to them, and by comparing the retrieved spatial and temporal seismological analyses and the DInSAR deformation measurements relevant to the considered seismic events.…”

Sequential Earthquake Damage Assessment Incorporating Optimized sUAV Remote Sensing at Pescara del Tronto

“…The October events caused significant damage primarily in the villages of Visso, Ussita, and Norcia [2,6], and exacerbated the damage in Pescara del Tronto. Other analyses of the 2016 earthquake sequence include geohazard forensics of Norcia in Barone and Di Maggio [9] as well as numerical modeling of ground deformation in Valerio et al [10], the mechanisms of the earthquakes in Zhong et al [11], and Amatrice building damage assessment using synthetic aperture radar (SAR) in Karimzadeh and Matsuoka [12]. The earthquake events appear in a gap between two recent M6.1 events-the 1997 Umbria-Marche earthquake to the north-west and the 2009 L'Aquila earthquake to the south-east.…”