Low-Frequency Ground Penetrating Radar for Active Fault Characterization: Insights from the Southern Apennines (Italy)

Highlights: What are the main findings? The integration of GPR data with precise georeferencing is effective in providing new constraints on the geometry and kinematics of shallow active faults in sedimentary deposits. In the case study area, the Calore River Valley (Southern Apennines), low-frequency GPR imaging revealed steeply dipping E–W to ENE–WSW normal faults, consistent with an active system, named Postiglione Fault System. What is the implication of the main finding? The results demonstrate the potential of low-frequency GPR to resolve near-surface fault architecture where surface evidence is scarce or ambiguous. These findings also contribute to refining the seismotectonic framework of the Southern Apennines, supporting improved seismic hazard assessment in one of the most seismically active regions of the Mediterranean. Ground Penetrating Radar (GPR) is a powerful tool for imaging shallow stratigraphic and structural features. This study shows that it is particularly effective also in detecting near-surface evidence of active faulting. In the Southern Apennines (Italy), one of the most seismically active regions of the Mediterranean area, the shallow expression of active faults is often poorly constrained due to limited or ambiguous surface evidence. Low-frequency GPR profiles were acquired in the Calore River Valley (Campania Region), an area historically affected by large earthquakes and characterized by debated seismogenic sources. The surveys employed multiple antenna frequencies (30, 60, and 80 MHz) and both horizontal and vertical acquisition geometries, enabling penetration depths ranging from ~5 m to ~50 m. The acquired GPR profiles, integrated with high-precision georeferencing, were able to reveal the presence of shallow steeply dipping active normal faults striking E–W to ENE–WSW, here named the Postiglione Fault System. Therefore, this study highlights the methodological potential of low-frequency GPR for investigating active faults in carbonate substratum and fine-to-coarse-grained sedimentary units and thus contributing to refining the seismotectonic framework and improving seismic hazard assessment of seismically active areas such as the Southern Apennines.