Testing the value of a multi-scale gravimetric analysis in characterizing active fault 2 geometry at hypocentral depths: the 2016-2017 Central Italy seismic sequence

Abstract

We report the results of a multidisciplinary investigation performed across the normal Quaternary faults that ruptured the surface during the August 24 (Mw 6.0) and October 30 (Mw 6.5), 2016 strong earthquakes in the Mt. Vettore-Mt. Bove areas, central Italy. Our aim is to test the effectiveness of the contribution of a multi-scale gravimetric analysis in characterizing seismogenic faults’ geometry at hypocentral depths on well-known outcropping faulty systems with known earthquake distribution. We adopted a multi-scale geophysical/geological approach consisting in the comparison of gravity lineaments inferred by Multiscale Derivative Analysis with the Quaternary structural setting mapped in the study area, the primary coseismic surface ruptures of the 2016-2017 sequence and the earthquakes’ epicentral distribution. Moreover, we performed a combined interpretation of 2D hypocentral sections of the 2016-2017 seismic sequences with images resulting from the Depth from Extreme Points method, to infer the faults’ geometry at depth. Based on our results, the investigated NW-SE Mt. Vettore-Mt. Bove fault system is dipping 60°-70° westward. We also detected the splays of this primary fault and its blind antithetic NW-SE structure, dipping northeastward. In the Norcia basin we highlight two main faults bordering the basin with a dip of about 45°. The one edging the eastern side dips westward, whereas the fault edging the western side dips eastward. Thanks to our analysis we could identify and characterize the geometry of the Norcia and Vettore master faults, as well as other blind/buried and/or silent faults that are related to the 2016 seismogenic structure. Our results show the effectiveness of this approach in potentially high-hazard areas that are structurally poorly known.