Geoelectric characterization of Quaternary basin bounded by active fault: TEst Site IRpinia fAult project

Abstract

In this study, we performed two electric resistivity tomography (ERT) profiles and a 3-D volume to characterize and reconstruct an active fault located at “Pantano di San Gregorio Magno”, an intramontane basin of  Southern Apennines, Italy, shaped by the active tectonics and hit by the Ms= 6.9, Irpinia 1980 earthquake, generated by a fault rupturing the soil in Pantano. The  overall Irpinia Fault has a  total length of about 40 km and with a thickness of the seismogenic layer of 8-10 km. The Irpinia Fault is among the faults with highest seismogenic potential in the Mediterranean region, causing the 4th Italian earthquake of last century (1980, Ms=6.9, Pantosti & Valensise, 1990) and generating a modest surface throw at Pantano San Gregorio Magno (SA). The basin is filled by lacustrine sediments, bassing laterally into alluvial fans and slope debris, laying over Mesozoic carbonate bedrock. The two 2D ERT surveys and the 3D volume allowed us to obtain high resolution images of the electrical resistivity of the subsoil both in 2D and in 3D. The results provided us with an opportunity to achieve a better understanding of the geometry of the active fault. The filling sediments are characterized by resistivity ranging from 10 to 150 Ohm m while the Mesozoic carbonate bedrock from 500 up to 1500  Ohm m. Furthermore, strong resistivity gradients are consistent with the tectonic structure characterizing the active fault.