GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione 2.2 411 that has been integrated with four electrical resistivity tomography (ERT) profiles (Fig. 2).The geomorphological analysis highlights the occurrence of features, e.g., aligned valleys, rectilinear scarps, that suggest the presence of a fault along the northeastern slope of the subdued ridge that bounds the Mt. Airola basin to the SW. The latter ridge is dissected by a wind-gap. Based on such evidence, the basin may be interpreted as an originally fault-bounded valley that, subsequently, developed as a karst basin. Surface evidence indicates that the basin is filled with colluvial deposits interbedded with pyroclastic layers.. Fig. 3 shows the geoelectrical profiles. In order to remove corrupting effects and to model the survey targets as accurately as possible, a numerical inversion was needed to convert apparent into real resistivities. In this work, a probability tomography method (RAOP) was used as a simple and fast anomaly source imaging tool (Mauriello et al ., 1999a, 1999b). The purpose of the technique is the design of an occurrence probability space of elementary anomaly sources, located anywhere inside an explored underground volume. In geoelectrics, the decomposition is made within a regular resistivity lattice, using the Frechet derivatives of the electric potential weighted by resistivity difference coefficients. The profiles allow identifying a sharp, high- angle contact between high resistivity rocks (carbonate bedrock) and low resistivity units, i.e., alluvial/colluvial Quaternary filling of the Mt. Airola basin. The sub-vertical contact may be interpreted as a roughly NE-dipping fault plane, consistent with surface geological evidence. In addition, profile G2 highlights the occurrence, below the surface rupture, of a concave up low resistivity body. Considering that this concave up body occurs below the carbonate ridge affected by the rupture, it could be interpreted either as a buried cavity or as water rich, fractured rocks of the damage zone occurring along the fault plane. Discussion and conclusion. The moderate magnitude Mw = 5.0, 29 December 2013 Matese earthquake has produced a large amount of seismically induced ground effects, that have affected an area of about 90 km 2 in the southeastern portion of the Matese ridge. Earthquake induced effects mainly consist of rock falls, some of which caused damages to local roads and to the aqueduct in the town of San Gregorio Matese, and include a coseismic rupture that affected the fault scarp bounding to the SW an intramontane basin located to the E of Mt. Airola. Geoelectrical investigations carried out in this area have allowed constraining the subsurface setting of the basin. Moreover, these data suggest that the coseismic rupture may be interpreted as the result of seismically induced either rock compaction of the fractured carbonate bedrock, or subdued collapse of a buried karst cavity, triggered by the Mw = 5.0, 29 th December 2013 earthquake. The spatial distribution of the ground effects, which cover an area of about 90 km 2 , allows the estimation of the epicentral intensity according to the ESI Scale (Michetti et al., 2007). The resulting evaluation is I = VIII ESI, a value exceeding by one degree the MCS scale intensity formerly evaluated by Convertito et al. (2014) based on damages to the man-made structures. References Cinque, A., Ascione, A. and Caiazzo, C.; 2000: Distribuzione spazio temporale e caratterizzazione della fagliazione quaternaria in Appennino Meridionale, in Galadini, F., Meletti, C. and Rebez, A. eds.: Le Ricerche del GNDT nel campo della pericolosità sismica, 203-218. Cinque, A., Patacca, E., Scandone, P. and Tozzi, M.; 1993: Quaternary kinematic evolution of the SouthernApennines. Relationships between surface geological features and deep lithospheric structures, Ann. Geophys., 36, 249-260. Convertito, V., Cubellis, E., Marturano, A., Obrizzo, F. and Petrazzuoli, S.M.; 2014: Terremoto del 29 dicembre 2013 nel Matese (MW = 5.0). Indagine speditiva degli effetti nell’area epicentrale e analisi preliminare della sequenza sismica, Rapporti Tecnici INGV, 290, ISSN 2039-7941. D’Amico, S., Cammarata, L., Cangemi, M., Cavallaro, D., Di Martino, R.M. and Firetto Carlino, M.; 2014: Seismic moment tensors and regional stress in the area of the December 2013– January 2014, Matese earthquake sequence (Italy), J. Geodyn., 82, 118-124. ISIDE, Italian Seismological Instrumental and parametric Data-basE, http://iside.rm.ingv.it/ (last accessed August 2016).