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

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).