Neo-deterministic seismic hazard assessment and earthquake occurrence rate

The aim of this study is to associate the expected ground motions from Neo-Deterministic Seismic Hazard Assessment (NDSHA) to robust estimates of their long-term average occurrence rates. NDSHA means scenario-based methods for seismic hazard analysis, where realistic and duly validated synthetic time series, accounting for source, propagation, and site effects, are used to construct ground motion scenarios. NDSHA, in its standard form, defines the hazard as the envelope ground shaking at the site, namely the maximum estimate computed from a large set of possible scenario earthquakes. Thus, the standard NDSHA maps provide rather robust and conservative hazard estimates, which do not require any assumption about the probabilistic model of earthquakes occurrence. Some specific applications, however, may benefit from temporal information about the computed ground shaking, including a gross estimate of its average recurrence time. For this purpose, the definition of the Frequency-Magnitude (FM) relation for earthquakes in the Italian region is performed according to the multi scale seismicity model and an occurrence rate estimate is associated to each of the modeled sources. The introduction of occurrence rate estimates in NDSHA also allows for the generation of ground shaking maps for specified time intervals (often improperly referred as "return periods") that permit a straightforward comparison between the NDSHA and the PSHA maps.