GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 2.1 GNGTS 2023 The interoperability tool We developed a tool (available online at https://diss.ingv.it/ithdiss/ ) that shows the potential physical links and interactions between the ACF and CSS datasets, relying solely on automatic geographic overlapping criteria. For this reason, there exist uncertainties concerning the actual structural relationships at depth among elements of the two datasets; therefore, the established links do not automatically imply that an earthquake generated by a segment of a certain CSS will certainly activate one of the connected surface active and capable faults. The links between the ACF and the CSS are updated regularly using a completely automatic procedure that exploits the available web services and uses the most updated versions of the two databases. The tool was developed as part of Task 3, Work Package 1 "Terremoti", of the 2019-2021 Agreement “B2” between the Italian Civil Protection Department and INGV. The Department has strongly encouraged this development, which indeed fills a gap in the SHA practice, both at a scientific and at a professional consulting level. As a matter of fact, these databases represent the preliminary references at national scale for seismic microzonation activities and for siting studies needed for critical infrastructure (either existing or planned). Method The active and capable faults of the ITHACA database were connected by an automatic geographic overlapping procedure to one or more CSS of the DISS database. The minimum overlap length was set to 10% of the total length of the fault. The procedure was run only for CSS whose upper tip depth is less than 15 km. This threshold was chosen based on the empirical evidence that deep seismogenic sources have a very low probability of causing primary surface ruptures or triggering distributed faulting. The automatic procedure constructs a buffer around the upper tip of the selected seismogenic sources, having a variable size depending on source geometry and kinematics. The size of the buffer corresponds to an area where the conditional probability of the potential occurrence of distributed faulting, calculated from the upper tip of the CSS considered as the primary fault, is above a minimal threshold. For normal and reverse/thrust faulting sources the hanging-wall dimension of the buffer has the same size as the surface projection of the source. Based on empirical studies (e.g. Petersen et al., 2011; Livio et al., 2017; Boncio et al., 2018), the footwall dimension was set at 4 km and 2 km for normal and reverse/thrust kinematics, respectively (areas shown in gray in the viewer). All high-angle strike-slip sources have a 3 + 3 km large buffer around the upper tip of the source, or the same size as the surface projection of the source if it is larger than 3 km. The size of the buffer in the two fault blocks was chosen following the probability function of distributed faulting, showing that at these distances probability is below a critical value (e.g. Youngs et al., 2003). The linked active/capable faults have been categorized by the compilers of the ITHACA database into three classes, using the “Rank” field of the ITHACA database (see Fig. 1):