High-resolution geophysical investigations in the central Apennines seismic belt (Italy): Results from the Campo Felice tectonic basin

The Campo Felice basin, in the central Apennines seismic belt (Italy), developed in the hangingwall of a 30 km-long system of NW-trending normal faults with Holocene paleoseismic activity and potential sources of M 6-7 earthquakes. We provide the first subsurface images of a key portion of the basin bounded by the Mt. Cefalone fault along two intersecting profiles trending NNE-SSW (CF-Dip, 1195 m-long) and WNW-ESE (CF-Strike, 1315-m long). We combined high-resolution depth-migrated reflection sections with P-wave velocity and electrical re-sistivity tomography models. CF-Dip profile displays a wedge-like syn-tectonic sedimentary sequence of alluvial and glacial deposits with Vp similar to 2500-3000 m/s and resistivity > 500 Omega m in the hangingwall of Mt. Cefalone fault, overlying a high-Vp (>4000 m/s) limestone bedrock similar to 300 m deep. The whole sequence displays reflectors truncated by the Mt. Cefalone fault zone and subsidiary antithetic faults. CF-Strike profile, tied to three 80-110 m-deep boreholes, shows a thick fluvio-lacustrine sequence with low-Vp (<2000 m/s) and low resistivity (<100 Omega m), and a bedrock that deepens to the southeast (>450 m). Single-station ambient noise measurements display Horizontal to Vertical Spectral Ratios with peaks at similar to 1 Hz, decreasing to similar to 0.8 Hz to the southeast in agreement with the bedrock deepening indicated by seismic profiling. According to our results, the Campo Felice basin is a deep asymmetric half-graben controlled by faulting whose activity likely started before the Middle Pleistocene. Our minimum displacement estimate accrued in the past 0.5 Ma by the Mt. Cefalone fault is in the range of similar to 100-250 m.