AN INTEGRATION OF GEOPHYSICAL METHODS FOR THE DETERMINATION OF SUBSURFACE STRUCTURE OF INTRA-MOUNTAIN BASINS: THE CASE OF LEONESSA PLAIN (CENTRAL APENNINES, ITALY)

About the thesis. This thesis describes the results of a research approach that integrated a detailed gravity survey with singlestation microtremor observations to evaluate the thickness of the alluviallacustrine sedimentary infilling, the bedrock structure of the Leonessa basin, and to reconstruct of the main steps of the basin evolution. The Leonessa basin, the test-area of this study, is located in the heart of the Central Apennines, in the northern Latium region. The city of Leonessa is located at 980 m a. s. l., about 36 km NNE of the town of Rieti, on the southern part of the homonymous basin. The Leonessa Plain is one of the major intra-mountain basins of Center Apennines, related to the Plio-Quaternary extensional tectonic. The area is characterized by a very high value of seismic hazard with respect to the rest of the Latium region, with a range of acceleration value between 0.25 – 0.278g (10% probability of exceedance in 50 years) on flat bedrock. According to the DGR n. 387 of May 22, 2009 “New Seismic Classification of the Territory of Latium Region”, the Leonessa city is classified as Seismic Area 1. During this research activity, it is intended to highlight the indispensable significance of the geophysical methods at the level of primary decision-making at urban planning studies and to help resolving a range of problems connected to risk assessment. To this purpose, 333 gravity stations and 29 single station microtremor observations were made to covered an area of 63 km2. Because of the complexity and active tectonic of the study area, an irregular valley shape was expected

The use of gravity prospecting to help the seismic microzonation studies of the Leonessa basin in Rieti, Italy.

A research approach that integrated different geophysical methods for local subsoil evaluation using for seismic microzonation studies was carried out in this research paper. The gravity prospecting were made to map and model the thickness of Quaternary deposits (gravel, sand and clay) overlaying the Meso-Cenozoic pelagic basin deposits of the Leonessa basin. The Leonessa basin is one of the major intermontane tectonic depressions of Central Apennines boarded on the southern side by the great normal fault, here referred to as the Leonessa fault. The study involved a test area of 32 km2 occupied by 250 gravity stations. The stations were accurately located with differential GPS (Ashtech Z-Xtreme dual-frequency GPS) that provided centimetric accuracy in elevation. The gravity measurements were performed using a LaCoste & Romberg gravimeter mod. D60 that has a reading resolution and an accuracy of 0.01 mGal. Measurements have been done in the depressions and also over the basement in or

A Multidisciplinary approach for the determination of subsurface structure of Leonessa Plain (Central Appennines, Italy).

n this study, detailed gravity survey and microtremor observations were made to map and model the thickness of Quaternary deposits (gravel, sand and clay) overlaying the Meso-Cenozoic pelagic basin deposits of the Leonessa plain. The study involved a test area of 50 km2 occupied by 300 gravity stations and by 30 sites of 3-component single-site observations. Stations were accurately located with differential GPS that provided centimetric accuracy in elevation. The microtremor data were analyzed by means of the horizontal-to-vertical spectral ratio (H/V). A realistic density of the unconsolidated Quaternary deposits (1.75-2,00 g/cm3) determined on core samples and a density of 2.60 g/cm3 for the basement limestone were used to constrain the 2D gravimetric models. The gravity and microtremor data were compared with a collection of existing well logs and geophysical data. The 2D models match quite well with the information determined from the previous works. The data obtained with these different methodological approaches allowed us to reconstruct the geometry of the depression and to evaluate the thickness of the Quaternary sedimentary infilling. Finally, on the basis of the obtained morphology, we were able to reproduce and to define the 3D model and the Quaternary evolution of the Leonessa plain.Published4T. Sismologia, geofisica e geologia per l'ingegneria sismicaN/A or not JC