Active and passive seismic methods to explore areas of active faulting. The case of Lamezia Terme (Calabria, southern Italy)

This paper presents the results of a geophysical investigation aimed to illustrate the architecture of the shallow stratigraphic horizons across an area believed to be crossed by a NW-SE trending trascurrent fault called the Lamezia Terme-Catanzaro Fault. In spite of the available information on fault segments and tectonic activity associated with faulting, the local scale fault characteristics are currently poorly known and the surface displacements are difficult to detect in a such a densely populated area. A traditional integrated geophysical exploration method was proposed as an effective solution to assist in the location of structures in the subsurface where surface geological and morphological evidence is inconclusive in terms of defining the location and the potential of the local seismogenic sources, responsible for recurrent catastrophic earthquakes. Two active High Resolution (HR) seismic reflection/refraction profiles were acquired using an array of vertical geophones with a Swept Impact Seismic Source (VibSist-500) in order to obtain seismic imaging of the subsurface of the study area. Additionally, passive Microtremor Array Method (MAM), deep wells and commercial seismic profiles were used to better constrain the geological trend of deeper seismostrata. The integrated interpretation of both geophysical and geological data allowed to infer subsurface pictures of the investigated areas identifying the depth of the seismic bedrock and characterizing the buried morphology, enhancing lineaments with possible relevance to faults. Discontinuities in the main horizons in seismic sections indicate that faulting is present in a Pliocene unit and may extend to the shallow subsurface in Quaternary sediments. The results of this study can provide a basis for earthquake prevention and construction work and demonstrate the applicability of the seismic methods to explore buried hidden faults in the perspective of applications on studies of physical stratigraphy of syn-tectonic deposits.