The role of 3D geological models in enhancing seismic risk assessment

The effects of seismic events can be devastating due to loss of human life, damage to cultural heritage and social fabric. Assessing seismic risk and developing mitigation strategies will remain a critical challenge of this century.

Earthquakes are complex natural phenomena resulting from the sudden release of energy originates typically from either a fault or faults system. Seismic ruptures occur at depth, triggering waves that propagate through the Earth’s crust and surface.

The characteristic of seismic waves, and then the shaking expected at specific interest location, depend on multiple geological factors, including the architecture of the fault source, rupture dynamics, and the properties of the rock volumes where waves propagate.

Numerous studies have shown that local geological features significantly influence the amplification of seismic waves, generating site effects. Such effects, as observed in recent earthquakes (i.e. Aquila, 2009, Mw 6.3), are particularly pronounced in sedimentary basins filled with alluvial material, where mechanical contrasts between host rock and overlying sediments reported.

In this study, we integrated geological and geophysical datasets to construct a preliminary 3D geological model of the Florence Basin (Italy). Oriented NW-SE, the basin is bounded by the Apennine chain to the northeast and the Chianti hills to the southwest. Preliminary analyses reveal both a complex substrate profile and geometry of the limits delimiting the sedimentary infill Units. Recent advances, including a well database with over 2,000 precise data points, detailed gravimetric profile and DEM, have enriched our understanding of the basin. The non-uniform substrate influences sediment thickness, which varies significantly due to the alternating lithologies formed in different depositional environments. This lithological complexity affects the physical and mechanical properties of the geological units, with important implications for seismic wave amplification. Amplification maps from recent microzonation studies highlight a marked zonation of seismic risk. However, these maps insufficient for studying the dynamic behavior of seismic waves in 3D.

Our work focuses on providing tools and methodologies for 3D geological modeling based on analyses of the Florence Basin, a complex case study. The results and approaches we present are crucial for improving seismic risk assessments in other basins. Enhancing local geological datasets has a significant impact on 3D numerical simulations of ground motion, contributing to more effective mitigation strategies and risk management.