Probabilistic Fault Displacement Hazard Analysis study in northern Calabria (Italy)

Northern Calabria (Italy) is an area with significant historical seismicity (Pollino / Sila Massif). While seismic hazard is now commonly assessed at both local and regional scales, fault displacement hazard also represents an important concern, particularly for critical infrastructure such as dams, bridges and nuclear facilities. In recent years, many efforts have focused on developing PFDHA (FDH initiative; IAEA benchmarks, etc.), leading to the development of several new prediction models.

In this study, we present a regional-scale assessment of fault displacement hazard, using an updated seismotectonic model derived from national fault databases (DISS, ITHACA) and published literature. We identify 11 potential seismogenic sources, of which 10 show normal kinematics and 1 is strike-slip. From these 11 potential sources, we explore 4 alternative source configurations, to account for uncertainty in fault activity. 

For the hazard calculations, we test various prediction models for surface rupture and surface displacement, for both ‘principal’ and ‘distributed' faulting. These models use different displacement metrics (AD/MD) and faulting definitions (principal, distributed, sum-of-principal, aggregated), making a direct inter-model comparison difficult. In addition to the regional-scale analysis and to overcome faulting definitions inconsistencies, we also investigate specific potentially critical sites (dams and bridges), enabling a more comprehensive comparison among models.

Results indicate that the fault displacement hazard is generally low, with return periods for significant displacement values (>10 cm) largely exceeding 10 kyr. The hazard is the highest along the surface fault traces (principal faulting) and decreases rapidly with distance from them (distributed faulting), emphasising the importance of having a reliable knowledge of surface traces of active and capable faults. We also highlight the high model variability, demonstrating the importance of using a logic-tree approach.