Testing three seismic hazard models for Italy via multi-site observations

Area of Science:

• Earth Sciences
• Geophysics
• Seismology

Background:

• Probabilistic seismic hazard analysis (PSHA) is crucial for quantifying earthquake risks globally.
• National-scale PSHA produces seismic hazard maps based on return periods, but differing models and data can lead to conflicting results, as seen in Italy.
• Validating PSHA at specific sites is challenging due to the rarity of extreme seismic events.

Purpose of the Study:

• To evaluate and compare three authoritative PSHA studies for Italy.
• To address discrepancies in seismic hazard maps by employing a regional validation approach.
• To test PSHA outputs against observed seismic activity frequencies.

Main Methods:

• A regional approach was adopted to overcome site-specific validation limitations.
• Probabilistic seismic hazard analysis (PSHA) predictions from three Italian studies were formally tested.
• Observed ground shaking exceedance frequencies, derived from approximately 50 years of seismic monitoring, were used for validation.

Main Results:

• The study found that seemingly different seismic hazard maps for Italy are statistically indistinguishable when validated against observational data.
• Formal tests comparing PSHA predictions with empirical exceedance frequencies showed consistency across the evaluated studies.
• The regional validation approach proved effective in assessing the reliability of national seismic hazard assessments.

Conclusions:

• The findings suggest that current authoritative PSHA studies for Italy, despite methodological variations, provide comparable seismic hazard information.
• Observed seismic activity frequencies support the general conclusions of the evaluated PSHA studies, reducing concerns about irreconcilable differences.
• The study highlights the value of regional validation using long-term seismic monitoring data for PSHA.