GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 2.1 GNGTS 2023 A 3D Smoothed Seismicity Model for the Adriatic Thrust zone, Italy C. Pandolfi 1 , M. Taroni 2 , R. de Nardis 1 , G. Lavecchia 1 , A. Akinci 2 1 DiSPuTer, Università degli Studi “G. d’Annunzio”, Chieti Scalo, Italy 2 Istituto Nazionale di Geofisica e Vulcanologia, Roma, Italy The smoothed seismicity is widely used to provide earthquake rate models as input for probabilistic seismic hazard assessments (PSHA) in regions with complex seismic source characterization (Akinci et al., 2018; Taroni and Akinci, 2021). It uses seismic catalogues to produce earthquake forecasts in time, space, and magnitude without relying on geological, tectonic, or geodetic information and overcomes the difficulties in characterizing and segmenting complex geological set-ups. This approach is constructed on a spatially 2D grid-based format in which each cell represents a possible seismogenic source able to generate earthquakes. Assuming that future rates will be similar to what is reported in earthquake catalogues (Kagan and Jackson, 1994; Frankel, 1995), the smoothed seismicity spatially smooths on the grid the location of past earthquakes to forecast future rates for each cell. Nevertheless, the standard smoothed seismicity approach may not properly present the seismicity rates for complex seismotectonic areas. Therefore, in this study, we propose an innovative 3D approach for fixed and adaptive smoothed seismicity methods. This approach presents a 3D kernel in the algorithm to smooth the location of earthquakes on a three-dimensional grid by considering the earthquake’s depth and spatial coordinates. The introduction of the third dimension in the smoothing process allows using a 3D spatial grid built on a fault surface 3D model to represent the depth variations of the structure and to provide also point-by-point the strike, the dip-angle, the rake, and the depth of the seismogenic layers derived from the fault 3D model and the associated seismic catalogue. The proposed 3D approach more accurately conveys a three-dimensional earthquake rate model with detailed rupture parameters of any seismogenic structure with a 3D surface model and related seismic catalogue. In this way, it allows for taking full advantage of seismotectonic models for seismic hazard evaluations. We tested our method to model the Adriatic Basal Thrust (ABT) in eastern Central Italy, a regional active contractional structure of which we have a well-constrained 3D model and a related high-quality location catalogue. The ABT is responsible for several historical and instrumental