UR 3.13 - MAXIMUM OBSERVABLE SHAKING (MOS) MAPS OF ITALY

Abstract

The main goal of UR 3.13 is to establish a work flow for a multi-layer map that includes the seismicity of Italy in terms of Maximum Observable Shaking (MOS), and the near-field/far-field boundaries (NF/FF) with respect to the major seismogenic faults mapped within the DISS database. Here we will discuss only the procedure to derive the MOS-map of Italy. Our approach merges updated knowledge on the Italian regional tectonic setting and on the Source Zone (SZ) definition and broadband scenario-like calculation of expected maximum shaking on a given area. For a given SZ, broadband ground shaking is computed for a rupture model derived from a Maximum Credible Earthquake (MCE) and its associated Typical Fault (TF). Amplitude spectra for deterministic Low Frequency and stochastic High Frequency waveforms are reconciled at intermediate frequency, where their domain of validity overlaps, to derive broadband synthetics and compute the associated shaking. As the MCE and TF float along the SZ, broadband ground motion is computed at each point surrounding the given fault and the maximum among observable shaking according to that scenario is plotted on the MOS map. So far the procedure was entirely successfully tested on the Macro Region MR4 (central-northern Apennine), while more detailed analysis is done on the MCE and TF suggested for the Colfiorito earthquake. Here our broadband ground motion scenario shows, besides a complex pattern of variation, a southwestern area of high PGA values, at about 20 km distance from the fault, likely associated to with the properties of the spatio-temporal complexity of the rupture process. For the purpose of the project a complete new map of SZ and MCE is under compilation, grouping seismogenic sources according to Mw and faulting mechanisms. This goal can be achieved most efficiently by targeted numerical simulations that cover the parameter range of interest (in terms of magnitude and distance etc) and consider a large suite earthquake rupture scenarios.