Abstract
We report the results of a multidisciplinary investigation performed across the normal Quaternary faults that ruptured the surface during the August 24 (M w 6.0) and October 30 (M w 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 hypocen- tral depths on well-known outcropping faulty systems with known earthquake distribution. We adopted a multi-scale geophysical/geo- logical approach consisting in the comparison of gravity lineaments inferred by Multiscale Derivative Analysis with the Quaternary struc- tural 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 im- ages 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 an- tithetic 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.
Highlights
Geological and geophysical techniques are important methods to characterize systems of active faults
The two westernmost mapped faults of the Norcia plain are correlated with discontinuous MDA maxima and with earthquake swarms mainly located along the easternmost fault of the basin
The areas characterized by a good correlation between MDA maxima, known geological features and earthquake clustering were better investigated by constraining the fault geometry at depth applying the DEXP imaging method combined with 2D hypocentral sections [Michele et al, 2016; Chiaraluce et al, 2017], and reflection seismic and balanced crosssections [Porreca et al, 2018]
Summary
Geological and geophysical techniques are important methods to characterize systems of active faults. Only limited portions of active faults are exposed at the surface, for the combined result of erosion and tectonic rock exhumation. The tectonically active regions of the central Apennines are characterized by Quaternary segmented normal fault-systems with low strain-rates. These fault segments generated linear hanging wall mountain fronts and bounded footwall basins filled by thick clastic covers [Boncio et al, 2004; Roberts and Michetti, 2004; Porreca et al, 2016]. Important details of the active fault structure are hidden beneath those intermountain basins. This might make the signature of recent faulting difficult to read. Geological cross-sections providing subsurface characterization combined with geophysical investigation (e.g., seismic reflection data and deep-well logs) can yield effective solution for better investigating
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