When probabilistic seismic hazard climbs volcanoes: the Mt. Etna case, Italy – Part 1: Model components for sources parameterization

Abstract

Abstract. The volcanic region of Mt. Etna (Sicily, Italy) represents a perfect lab for testing innovative approaches to seismic hazard assessment. This is largely due to the long record of historical and recent observations of seismic and tectonic phenomena, the high quality of various geophysical monitoring and particularly the rapid geodynamics clearly demonstrate some seismotectonic processes. We present here the model components and the procedures adopted for defining seismic sources to be used in a new generation of probabilistic seismic hazard assessment (PSHA), the first results and maps of which are presented in a companion paper, . The sources include, with increasing complexity, seismic zones, individual faults and gridded point sources that are obtained by integrating geological field data with long and short earthquake datasets (the historical macroseismic catalogue, which covers about 3 centuries, and a highquality instrumental location database for the last decades). The analysis of the frequency-magnitude distribution identifies two main fault systems within the volcanic complex featuring different seismic rates that are controlled essentially by volcano-tectonic processes. We discuss the variability of the mean occurrence times of major earthquakes along the main Etnean faults by using an historical approach and a purely geologic method. We derive a magnitude-size scaling relationship specifically for this volcanic area, which has been implemented into a recently developed software toolFiSH (Pace et al., 2016) -that we use to calculate the characteristic magnitudes and the related mean recurrence times expected for each fault. Results suggest that for the Mt. Etna area, the traditional assumptions of uniform and Poissonian seismicity can be relaxed; a time-dependent fault-based modeling, joined with a 3-D imaging of volcano-tectonic sources depicted by the recent instrumental seismicity, can therefore be implemented in PSHA maps. They can be relevant for the retrofitting of the existing building stock and for driving risk reduction interventions. These analyses do not account for regional M > 6 seismogenic sources which dominate the hazard over long return times (≥ 500 years).

Seismic Hazard Analyses From Geologic and Geomorphic Data: Current and Future Challenges

“…In the following sections we describe the fundamentals of earthquake scaling, describe key factors that control differences in magnitude scaling, provide an overview of the main types of scaling relations that have been developed in the last couple decades, and provide some ideas as to where the general topic area is going in the future. Magnitude-on-rupture-length scaling relation for the Etna region of Italy (Azzaro et al, 2017). The equation of the line is M w = 3.39 + 2.08log(L), with a standard error of 0.39 on magnitude (M w ), and L represents length.…”

Major explosions and paroxysms at Stromboli (Italy): a new historical catalog and temporal models of occurrence with uncertainty quantification

“…The exponential class represents the inter-event distribution of a classical Poisson process. This is a common choice, but restrictive 27 , 40 . Furthermore, the short-term analysis of the explosive activity at Stromboli indicates that the system exhibits some memory 75 , 76 .…”

Surface ruptures database related to the 26 December 2018, MW 4.9 Mt. Etna earthquake, southern Italy

“…However, in a volcano-tectonic setting such as Etna, surface ruptures can be associated even with moderate-sized earthquakes having recurrence times of a few years 5 . This circumstance allowed us to collect new data sets able to improve empirical scaling relationships for small events [23][24][25][26] . Moreover, the collected data are precious to fulfil the primary objective of Fault Displacement Hazards Analysis (FDHA), aimed at quantifying the spatial distribution and magnitude of surface displacements caused by earthquake faulting and their impact on structures and critical Fig.…”