GNGTS 2015 - Atti del 34° Convegno Nazionale

GNGTS 2015 S essione 2.1 Towards a new generation of seismic hazard maps for the volcanic region of Mt. Etna R. Azzaro 1 , G. Barberi 1 , O. Cocina 1 , S. D’Amico 1 , R. Gee 2 , H. Langer 1 , S. Lombardo 3 , M.G. Ordaz-Schroeder 4 , B. Pace 5 , F. Panzera 3 , L. Peruzza 2 , A. Saraò 2 , M.L. Suarez 4 , G. Tusa 1 , T. Tuvè 1 1 INGV Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo, Catania, Italy 2 OGS Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, Sgonico (TS), Italy 3 Dip. di Scienze Biologiche, Geologiche e Ambientali, Università di Catania, Italy 4 UNAM Universitad Nacional Autonome de México, Mexico City, Mexico 5 DiSPUTer, Università degli Studi “G. d’Annunzio” Chieti-Pescara, Chieti, Italy Introduction. In the last years, several seismic hazard analyses have been undertaken at Mt. Etna volcano in Sicily, Italy. These studies were aimed at estimating the capability of local faults to generate destructive earthquakes especially in the mid-term (30-5 years). Even if the areas prone to high seismic hazard have small extension, they give useful indication to establish priority criteria for seismic risk reduction action and land planning at the local/regional scale. Two main methodologies were applied in the past: the first is based on macroseismic data and uses a historical probabilistic approach (the “site approach”, see Azzaro et al. , 2008, 2015); the second is based on a seismotectonic probabilistic approach, with time-dependent fault-based modelling, in which occurrence probabilities of major earthquakes are estimated by historic inter-event times, through a Brownian Passage Time (BPT) model combined with the time elapsed since the last event (Azzaro et al. , 2012b, 2013). In the framework of INGV-DPC V3 Project, in two annual phases started in 2012 and ended in 2015, we performed a new full probabilistic seismic hazard assessment (PSHA) by using original definition of seismic sources (fault, areas, point sources), updated ground-motion prediction equations (GMPE) for this volcanic area, and referring to Poissonian and time- dependent occurrence models. Final results are given in term of maps for mid to short exposure times (10% exceeding probability in 30, 20, 10 and 5 years) and several spectral amplitudes. Site effects have been partially included too, at the very last stage of the project. Working in a volcanic area implies new problems, usually discarded by standard PSHA, so we have tried to fix them with new analyses and original tools, as it will be briefly described hereinafter. Novelties concern both the sources parametrization, and GMPEs. Characterization of the seismic sources. We defined the seismogenic sources related to volcano-tectonic seismicity, with increasing degree of detail and complexity. For this purpose, we used both long-term (macroseismic catalogue) and short-term data (instrumental catalogue) of the Etnean earthquakes. The latter data set consists of earthquakes recorded by the seismic network of Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo (INGV-OE) from 2005 to 2014 (Gruppo Analisi Dati Sismici, 2014; Alparone et al. , 2015), which have been then re-located with a 3-D model of seismic wave velocities. The conceptual tree adopted for the hazard elaborations is summarized below: • Branch 1. Areal seismic sources with Gutenberg-Richter relationships (GR) calibrated on instrumental ( a - b -values) and historical data (maximum magnitude M max ). This approach is similar to the one used by the Italian seismic hazard map MPS04 (Stucchi et al. , 2011). • Branch 2. Fault geometry and characteristic earthquake model for major seismicity based on (a) historical and (b) geometric-kinematic approaches. Areal seismic sources for background seismicity (M < 4.5). • Branch 3. Fault geometry and characteristic earthquake model for major seismicity based on (a) historical and (b) geometric-kinematic approaches. Diffused seismicity modelled by point sources with a generalized non-Poisson model, for background seismicity (M < 4.5). Areal seismic zones (hereinafter seismogenic zone, SZ) represent the simplified geometry of the main seismogenic fault systems recognized in the Etnean area (Timpe and Pernicana faults,