The San Vittorino Sinkhole Plain: relationships between bedrock structure, sinking processes, seismic events and hydrothermal springs

Abstract

The San Vittorino Plain is located along the Velino River Valley within an intermontane depression, filled with continental deposits. This plain is characterized by the presence of numerous sinkholes, often filled with mineralized spring waters. From a structural point of view, the study area is characterized by four tectonic units with different paleogeographical evolution and deformation styles. From the innermost unit they are: the Reatini Unit, the Navegna Unit, the Salto Unit, and the Nuria Unit. The main tectonic lineaments are represented by the Anzio-Ancona line, the Olevano-Micciani line, the Fiamignano-Micciani Fault and the Cerquara-Piedimozza Fault. The development of sinkholes in the study area is mainly due to deep suffusion and deep piping processes, linked to fluid upwelling along fracture-fault systems and to dissolution (by H2S and CO2) in the continental deposits. The sinkhole distribution suggests that they are mainly formed in a collapsed sector of the Mt. Paterno block whose structural setting, characterized by several splays, with marly-clayey and siliciclastic deposits at the footwalls, favoured the development of confined aquifers. The rise of groundwater to the surface along the network of faults and fractures crossing the carbonate bedrock is likely controlled by hydrostatic pore pressures, which may be strongly increased by earthquake shaking. The surface distribution of sinkholes in the San Vittorino Plain, showing differences within the study area, is strictly linked to the bedrock structure and the related hydrogeological setting, as demonstrated by the detailed survey carried out in the area.