GNGTS 2021 - Atti del 39° Convegno Nazionale

GNGTS 2021 S essione 2.1 224 FAULT2RISK - CLOSING THE LOOP BETWEEN SEISMIC HAZARD MODELERS AND EARTHQUAKE GEOLOGIST O. Scotti 1 , F. Visini 2 , J. Faure Walker 3 , L. Peruzza 4 , B Pace 5 , L. Benedetti 6 , P. Boncio 7 , G. Roberts 8 1 Bureau d’Evaluation des Risques Sismiques pour la Sûreté des Installations, IRSN, Fontenay-aux-Roses, France 2 Istituto Nazionale di Geofisica e Vulcanologia, Pisa, Italy 3 Institute for Risk and Disaster Reduction University College London, London, UK 4 National Institute of Oceanography and Applied Geophysics - OGS, Italy 5 InGEO Department, Università degli Studi G. d’Annunzio Chieti e Pescara, Chieti, Italy 6 Aix-Marseille Université, CEREGE CNRS-IRD UMR 34, Aix en Provence, France 7 DiSPUTer Department, Università degli Studi G. d’Annunzio Chieti e Pescara, Chieti, Italy 8 Department of Earth and Planetary Sciences, Birkbeck College, London, UK The aim of the Fault2SHA European Seismological Commission Working Group Central Apennines laboratory is to enhance the use of geological data in fault-based seismic hazard and risk assessment and to promote synergies between data providers (earthquake geologists), end-users and decision-makers. To this aim, by using the Fault2SHA Central Apennines Database (Fault2SHA CAD Faure Walker et al. 2020; 2021) where geologic data are provided in the form of characterized fault traces, grouped into faults and main faults, with individual slip rate estimates, we proposed a methodology for calculating multi fault-based seismic hazard that allows for the inclusion of detailed locations of active faults and multiple measures of slip-rate along a fault and a visualisation of the results (Scotti et al., 2021). We here present the workflow of the methodology: how data from the Fault2SHA CAD is used to build slip rate profiles, define main fault sections, parametrize deformation models, compute multi-fault rupture scenarios and evaluate seismicity rates. We first derived slip rate profiles for each main fault in the Fault2SHA CAD, and assumed that the geological slip rate of faults estimated at the surface can be used to estimate the overall deformation rate accommodated by earthquakes in the fault system. Drawing the slip rate profile involved two steps. In the first step we assume that slip rates tend to zero at tips of the main fault by adding points of zero slip rate at both tips. In the second step, we obtain a slip rate profile by linear interpolation of the slip rate data points similarly to Faure Walker et al. (2010). We then calculated slip rate profiles for the minimum, preferred and maximum values of slip rates along the main fault. Main faults are then divided into distinct sections of length comparable to the seismogenic depth to allow consideration of variable slip rates and the exploration of multi-fault ruptures in the computations. The Fault2SHA CAD does not provide seismogenic thickness, therefore we considered two hypotheses for a 10 and 15 km thick seismogenic layer, consistent with relocated seismicity (Pizzi et al., 2017) distribution and thermo-mechanical analyses (Boncio et al., 2009), thus exploring two different deformation models. For the other parameters, we considered simplifying assumptions: we assigned to each main fault the average of the dip measurements contained in the database, with a constraint that dips do not exceed 55° to account for the fault plane geometries imaged by recent seismic sequences (e.g., Chiaraluce et al., 2011; Improta et al., 2019). We attributed a slip rate to each main fault -section by computing the minimum, preferred and maximum slip rate profiles, then integrating over each main fault -section to obtain a single slip-rate value for each. In this presentation we considered only one branch of the uncertainties affecting each step of the computation procedure, in particular we only considered the mean slip rate profile for hazard and risk analysis. To build a deformation model we then need to define a list of earthquake ruptures comprising either single main faults -section or possible combinations of main faults -sections. Following the analysis of fault steps, gaps, and bends along fault ruptures of Biasi and Wesnousky (2016), Biasi andWesnousky (2017), we assumed that to be part of a potential earthquake rupture, main faults