Ground penetrating radar investigations to study active faults in the Norcia Basin(Central Italy)

A ground penetrating radar (GPR) survey was conducted across the Quaternary intramountain graben of the Norcia basin (Italy) in an effort to locate an active fault zone and to investigate the shallow geological structures. Measurements over an exposed (trenched) fault identify a radar signature consisting of hyperbolic diffractions in correspondence with the main fault's position. The migrated profile shows a good spatial correlation with the known fault at a control site. The average wave velocity of radar impulses in the ground was obtained by comparing with the field scans of real traces two synthetic signals, one at the hanging wall and one at the footwall of the fault. This analysis made possible to estimate the thickness of the sedimentary layers involved in the fault mechanism and the stratigraphic throw of the fault itself. The combined use of GPR across the probable northern continuation of the fault, with the information obtained with the study in the exposed fault, was used to select the location of new trench excavations. The GPR, being a relatively easy, non-invasive and high-resolution technique, can thus be used in palaeoseismological investigations, particularly for a preliminary investigation where the geological context is poorly defined