The MCS intensity distribution of the devastating 24 August 2016 earthquake in central Italy (MW 6.2)

Abstract

<p>Here we describe the macroseismic survey of the 24 August 2016 earthquake in central Italy (M_W 6.2). By applying a revised version of the Mercalli-Cancani-Sieberg scale, we estimated the site intensity in more than 300 localities of Lazio, Abruzzi, Umbria and Marche regions, providing the Civil Protection with a quick and robust snapshot of the earthquake. The most severe effects are focused south of the instrumental epicenter, in the Amatrice intermountain basin, where intensity reached 10-11 MCS. Highest damage (area inside 9 MCS isoseismal) is focused in a NNW-SSE belt of the hangingwall of the causative faults, i.e. the southern segment of the Mount Vettore fault system and the northern segment of the Laga Mounts fault system, with northward damage propagation in the far-field. The intensity dataset allows to evaluate a M_W 6.16±0.5, which is very close to the instrumental magnitude, with a seismogenic box striking N161°, mimicking the geological active faults. Epicentral intensity is I_0 10 MCS, I_MAX 10-11. The elevated level of destruction is mainly due to the high vulnerability of buildings, mostly made by cobblestone masonry. Integrating the macroseismic information with the geological, geodetical and geophysical data it is possible to hypothesize a bidirectional rupture propagation (toward NNW and SSE) along the two different faults. It is also possible to attribute the 1639, M_W 6.0 earthquake to the same source of the southern 2016 rupture (northernmost Laga Mounts faults).</p>

Spatial-Temporal Evolution of Extensional Faulting and Fluid Circulation in the Amatrice Basin (Central Apennines, Italy) During the Pleistocene

“…In addition, the diachronic deposition of the continental deposits cannot be excluded over the Amatrice Basin, being influenced by the hydrodynamics of local alluvial drainages (e.g., Cacciuni et al, 1995;Mancini et al, 2019). Finally, we aware that our ages do not preclude the fact the AFS (or its segments) reactivated during the Holocene, in consequence to the seismogenic activity of the adjacent Gorzano-Laga Fault (e.g., Galli et al, 2016). Further geochronological constraints and/or geomorphic analyses could be addressed to elucidate possible minor activations of the AFS connected to the seismic activity in the Amatrice Basin.…”

“…The coseismic deformation was heterogeneously distributed along both these faults, with estimated fault length activated of ∼30 km and maximum offset of ∼2 m along the Vettore Fault, and estimated fault length activated < 2 km and maximum offset < 20 cm for the Gorzano-Laga Fault (Emergeo Working Group, 2016;Lavecchia et al, 2016;Pizzi et al, 2017;Pucci et al, 2017;Civico et al, 2018). The modes and styles how the Vettore and the Gorzano-Laga faults evolved over space and time include bilateral ruptures between them, inducing the progressive lengthening of the surface segments through the propagation of the fault tips (Galli et al, 2016;Tinti et al, 2016;Cheloni et al, 2017;Pizzi et al, 2017;Perouse et al, 2018). At depth, both faults are imaged to merge into a unique tectonic structure that links at seismogenic depths of about 7-9 km (Lavecchia et al, 2016;Chiaraluce et al, 2017), where the localization of deformation are likely conditioned by the occurrence of inherited regional structures (e.g., Bigi et al, 2013;Pizzi et al, 2017;Buttinelli et al, 2018;Falcucci et al, 2018;Bonini et al, 2019).…”

“…Structurally, these intermountain basins reside at the hanging wall of regional (tens km-long) NW-SE-striking extensional faults. Deformation, displacement, and basin subsidence are accommodated both along the main basin-bounding faults and along secondary (antithetic or synthetic) collateral faults that are distributed throughout the basins (e.g., Calamita and Pizzi, 1994;Cello et al, 1997;Barchi et al, 2000;D'Agostino et al, 2001;Galadini and Galli, 2003;Boncio et al, 2004a,b;Galli et al, 2005;Blumetti and Guerrieri, 2007;Galli et al, 2016).…”

“…No major (i.e., Mw > 4) historical earthquakes were associated to the Vettore Fault before the 2016-2017 sequence (Galli et al, 2019). On the other hand, the 1639 Amatrice earthquake (Mw 6.0) has been attributed to the seismogenic activity of the northwestern segment of the Gorzano-Laga Fault, based on the analysis of the regional seismic records (Boncio et al, 2004a), macroseismic surveys and geological evidences (Galli et al, 2016).…”

“…The major amount of coseismic deformation was accommodated over the northwestern part of the area, i.e., along the Vettore Fault and the adjacent syn-tectonics Castelluccio and Norcia basins (e.g., Pizzi et al, 2017;Pucci et al, 2017;Smeraglia et al, 2017;Civico et al, 2018;Perouse et al, 2018;Villani et al, 2018;Galli et al, 2019). Coseismic ruptures also involved the southeastern part of the area (Emergeo Working Group, 2016;Galli et al, 2016;Lavecchia et al, 2016;Pizzi et al, 2017) i.e., along the Gorzano-Laga Fault and the adjacent Amatrice Basin, the latter still representing an under-explored syn-tectonic depression in terms of its structural setting.…”