Territorial exceedance of probabilistic seismic hazard from ShakeMap data.

Area of Science:

• Earthquake Engineering
• Seismology
• Geophysics

Background:

• Seismic structural design relies on ground motion intensity with a defined probability of exceedance or return period.
• Probabilistic seismic hazard analysis (PSHA) generates maps of design intensities for specific return periods.
• Probability theory suggests a predictable fraction of sites will exceed design intensities within a given time frame.

Purpose of the Study:

• To quantify the areal fraction of Italian territory exposed to design intensity exceedance using three nationwide PSHA models.
• To compare this fraction for instrumental earthquakes (2008-2019) and historical earthquakes (nearly 1000 years).
• To assess the consistency of exceedance fractions across different PSHA models and earthquake catalogs.

Main Methods:

• Utilized ShakeMap data for instrumental earthquakes to estimate exceedance fractions.
• Developed inferred ShakeMaps for historical earthquakes over a 1000-year period.
• Calculated the areal fraction of Italian territory exceeding design intensities for each PSHA model and earthquake type.

Main Results:

• The estimated areal fraction of Italian territory exposed to design intensity exceedance was quantified for three PSHA models.
• Comparable exceedance fractions were found between instrumental and historical earthquake data.
• Despite differences in hazard models, the estimated fractions of territory exposed to exceedance were consistent across all models.

Conclusions:

• The study demonstrates a comparable areal fraction of territory exposed to seismic design intensity exceedance across Italy.
• Findings support the robustness of PSHA models, showing consistency between recent instrumental and long-term historical seismic hazard assessments.
• The results validate the reliability of current seismic hazard assessment methodologies for national-scale applications.