Busetti, Martina

In recent years, new approaches for developing earthquake rupture forecasts (ERFs) have been proposed to be used as an input for probabilistic seismic hazard assessment (PSHA). Zone- based approaches with seismicity rates derived from earthquake catalogs are commonly used in many countries as the standard for national seismic hazard models. In Italy, a single zone- based ERF is currently the basis for the official seismic hazard model. In this contribution, we present eleven new ERFs, including five zone-based, two smoothed seismicity-based, two fault- based, and two geodetic-based, used for a new PSH model in Italy. The ERFs were tested against observed seismicity and were subject to an elicitation procedure by a panel of PSHA experts to verify the scientific robustness and consistency of the forecasts with respect to the observations. Tests and elicitation were finalized to weight the ERFs. The results show a good response to the new inputs to observed seismicity in the last few centuries. The entire approach was a first attempt to build a community-based set of ERFs for an Italian PSHA model. The project involved a large number of seismic hazard practitioners, with their knowledge and experience, and the development of different models to capture and explore a large range of epistemic uncertainties in building ERFs, and represents an important step forward for the new national seismic hazard model.

The zonation presented in this study has been developed with the aim of applying it as a branch of the logic tree that will be used for the new Italian seismic hazard map, presently in preparation according to the approach of seismotectonic probabilism. With respect to the zonation used for the present official seismic hazard map of Italy, the zonation proposed here considers narrower sources and is based on new and updated seismological data. In particular, some new seismogenic zones are proposed here, introducing areas that were not considered seismogenic until now (e.g., the narrow sources characterised by the presence of transform faults which are almost normal to the trend of the northern Apennines). The preliminary seismic hazard estimates produced with this new zonation aim to identify possible problems that the zonation introduces in the seismicity characterization of the seismogenic zones. As the present seismic hazard assessment was computed by considering a different attenuation model with respect to the one applied for the previous national seismic hazard maps, a re-elaboration of the most recent map referring to Italy has been developed: the comparison of the two maps is a good indicator of the areas where additional seismological investigation is needed to support the zonation presented here. In particular, some zones are not adequately documented with regard to seismicity and a different computation of the seismicity rates is suggested.

Deep-sea ridges-channel systems have been recognized in some places on the continental rise around Antarctica. They are object of interest because of their relation to the ice sheet dynamics and their generally continuous record of paleo-climatic changes. The Wilkes Land continental margin is one of the areas where these morphological features are well developed; it is also particularly important because of its location close to the Mertz Glacier, which is one of the few outlet glaciers of the Eastern Antarctic Ice Sheet. The Wilkes Land continental margin was investigated induring the Austral Summer 2000 by the joint Australian and Italian WEGA(WilkEs basin GlAcial history) Project, onboard the R/V Tangaroa. During this cruise, about 600 km of multichannel seismic reflection profiles, 3.5 kHz acoustic profiles and 11 piston cores with trigger cores were acquired on the continental rise (Fig. 1). The Wilkes Land continental margin morphology is characterised by several submarine canyons cutting the slope while the lower rise, investigated by the WEGA Project, is characterised by a network of generally low relief channels separated by large sediment ridges. The detailed bathymetric map of the rise area shows three ridges named from west to east respectively “C”, “A” and “B”, bounded by the Jussie Canyon, the WEGA Channel and the Buffon Canyon (Fig. 1). This channel-ridge system has an approximately North-South elongation, perpendicular to the continental margin. The sediment ridges are ca. 150 km in length and more than 40 km of width and their relief is about 1000 meters in the proximal part, decreasing to ca. 300 meters offshore. They are asymmetrical, showing a long gentle eastern flank and a short steep western side, lying between 2500 and 3600 meters water depth in the upper and lower part respectively. The Jussie Canyon and the Buffon Canyon reach the shelf break, while the WEGA Channel seems to start lower, in the upper rise.