Evaluation of Probabilistic Site-Specific Seismic-Hazard Methods and Associated Uncertainties, with Applications in the Po Plain, Northern Italy

摘要

Site-specific ground-motion hazard, as assessed by a probabilistic seismic-hazard analysis one-step approach that handles a single-site sigma and its uncertainties and uses a simple logic tree, is compared with a two-step approach that includes bedrock motion evaluation and wave propagation through a local soil profile with consideration of the main epistemic uncertainties. The one-step analysis relies on accelerometer data from the Po Plain, a sedimentary basin in northern Italy where an earthquake sequence with two M-w similar to 6.0 events was extensively recorded in 2012. Uniform hazard spectra (UHS) on soil and exposed bedrock are evaluated at three deep-soil accelerometer sites (MRN, NVL, and T0821), using residual measures available from other studies, by which uncertainties in site terms (delta S2S) and single-site sigma (sigma(ss,s)) are estimated. Despite similarity in geologic conditions, at least one out of three sites in the one-step analysis displays substantial differences in mean level (T0821) or in the (84-16) percentile spread (NVL), depending on differences in site terms and single-site sigma, possibly caused by source-to-site propagation effects.