Abstract
This paper describes the main findings of the project HYPSTHER (HYbrid ground motion prediction equations for PSha purposes: the study case of souTHERn Italy; supported by the Italian Institute of Geophysics and Volcanology). The goal of the project is to develop a methodological approach to retrieve hybrid Ground Motion Prediction Equations (GMPEs) based on integration of recorded and synthetic data. This methodology was applied to the study area of southern Italy, focusing on the southern Calabria and Sicily regions. The target area was chosen due to the expected high seismic hazard levels, despite the low seismic activity in recent decades. In addition, along the coast of the study area, there are many critical infrastructures, such as chemical plants, refineries, and large ports, which strongly increase the risk of technological accidents induced by earthquakes. Through the synthetic data, the predictions of the hybrid GMPEs have been improved under near-field conditions, with respect to empirical models for moderate to large earthquakes. Attenuation at distances greater than 50 km is instead controlled by the empirical data, because attenuation is faster with distance. The aleatory variability of the hybrid models has strong impact on probabilistic seismic hazard assessment, as it is lower than the sigma of the empirical GMPEs. The use of the hybrid GMPEs specific for the study area can produce remarkable reductions in hazard levels for long-return periods, mainly due to changes in median predictions and reduction of the aleatory variability.
Highlights
The calibration of reliable Ground Motion Prediction Equations (GMPEs) in regions of interest have become a critical issue in Probabilistic Seismic Hazard Assessment (PSHA)
No selection criteria are applied to the EXSIM dataset, As the simulations are performed for outcropping rock without topographic amplifications, we considered only the recorded data relative to the reference rock (RR) stations (Figure 17, blue circles), which corresponds to about 180 records
The SI17hyb predictions are significantly different from SI17ref under near-field conditions, as the hybrid GMPEs are better constrained by the simulated data, with larger median values
Summary
The calibration of reliable Ground Motion Prediction Equations (GMPEs) in regions of interest have become a critical issue in Probabilistic Seismic Hazard Assessment (PSHA). In areas characterized by high hazard levels where few significant earthquakes have occurred in recent years or where the recording networks are not dense, empirical data can be scarce, and the use of synthetic ground-motion parameters can provide a way to represent ground motion in regions of interest. A common approach to obtain a hybrid description of ground motion in a given area is the host-to-target method [6] This calibrates an empirically well-constrained GMPE in a data-rich host region for use in a data-poor target region, based on adjustment factors that are obtained from response–spectral ratios of stochastic simulations in the host and target regions. Sensitivity analysis is performed to evaluate the impact on the seismic hazard assessment of the study area, using different GMPEs derived from empirical or hybrid (i.e., recorded and simulated) data. The hazard variability is evaluated considering two different return periods (TR ) for strategic infrastructures, according to the European (EC8, [10]) and Italian (NTC08, [11]) seismic codes, which correspond to damage and collapse-limit states
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