An Integration of Geophysical Methods for the Determination of Subsurface Structure of the Intra-Mountain Plains: The CASES of Rieti and Leonessa (CENTRAL APENNINES, ITALY)

Abstract:

This work, carried out with an integrated methodological approach, describes the acquisition of gravity data and their integration with different geophysical techniques, in order to map and model the thickness of unconsolidated deposits and determine the bedrock configuration of two different intra-mountain plains: Leonessa plain (hereafter LP) and Rieti plain (hereafter RP).

The LP and the RP, the test areas of this study, are typical intra-mountain depressions of Center Apennines, related to the Plio-Quaternary extensional tectonic. Both basins are characterized by thick Quaternary fluvial-lacustrine deposits (gravel, sand and clay) overlaying the Meso-Cenozoic pelagic basin deposits.

On the LP, the study involved an area of 62 km² occupied by 333 gravity stations. Instead, on the RP, the study area, of 35 km², were occupied by 170 gravity stations. The gravity data resulted from the network adjustment were used to calculate the Bouguer anomaly map. Subtracting the regional field from the Bouguer anomaly produced the residual anomaly map.

In order to determine the distribution of the sedimentary infill, a 2D gravity modeling was developed in the region, including five profiles in the case study of LP and six profiles in the case study of RP. A realistic density of the unconsolidated Quaternary deposits (1.75-2,00 g/cm³ in the case of LP and 2,15 g/cm³ in the case of RP), a density of 2.50 g/cm³ for the Travertine and a density of 2.60 g/cm³ for the Meso-Cenozoic pelagic basin deposits were used to constrain the 2D gravimetric models. The models match quite well with the information determined from a collection of existing well logs and geophysical data obtained by the ambient noise, MASW and Downhole measurements.

Finally, referring to these models, we were able to evaluate the thickness of the Quaternary sedimentary infilling and to define the 3D bedrock configuration of the basins. These 3D models represent a useful starting point for future activities such as microzonation or seismic hazard studies.