Style of faulting of expected earthquakes in Italy as an input for seismic hazard modeling

Abstract

Abstract. The style of faulting and distributions of nodal planes are essential input for probabilistic seismic hazard assessment. As part of a recent elaboration of a new seismic hazard model for Italy, we defined criteria to parameterize the styles of faulting of expected earthquake ruptures and to evaluate their representativeness in an area-based seismicity model. Using available seismic moment tensors for relevant seismic events (Mw≥4.5), first arrival focal mechanisms for less recent earthquakes, and also geological data on past activated faults, we collected a database for the last ∼100 years by gathering a thousand data points for the Italian peninsula and regions around it. In this dataset, we adopted a procedure that consists, in each seismic zone, of separating the available seismic moment tensors into the three main tectonic styles, making a summation within each group, identifying possible nodal plane(s), taking into account the different percentages of styles of faulting, and including where necessary total or partial (even in terms of tectonic style) random source contributions. Referring to the area source model used, for several seismic zones we obtained robust results; e.g., along the central and southern Apennines we expect future earthquakes to be mostly extensional, although in the outer part of the chain reverse and strike-slip events are possible. In the northern part of the Apennines we expect different styles of faulting for different hypocentral depths. In zones characterized by a low seismic moment release, the possible style of faulting of future earthquakes is less clear and it has been represented using different combinations of random sources. The robustness of our results is confirmed when compared with recent relevant earthquakes occurring in Italy.

Earthquake Rupture Forecasts for the MPS19 Seismic Hazard Model of Italy

“…The complex interaction among the three plates is still ongoing, with the Nubia and Eurasian plates that are converging at a rate of about 10 mm/yr along a NNW-SSE direction [DeMets et al, 1990;Serpelloni et al, 2005;Billi et al, 2011;Palano, 2015;Scarfì et al, 2018]. The current seismotectonics of Italy reflects the complex geodynamic regional setting, as documented by presentday stress indicators [e.g., Carafa and Barba, 2013;Mariucci and Montone, 2020] and focal mechanisms [e.g., Pondrelli et al, 2020;Roselli et al, 2018]. As shown in Figure 1, shallow extensional focal mechanisms and normal faulting prevail along the axial portion of the Apennines from northern Italy to the northernmost part of Sicily.…”

An Integrated Multiscale Method for the Characterisation of Active Faults in Offshore Areas. The Case of Sant’Eufemia Gulf (Offshore Calabria, Italy)

“…Active deformation data (GPS, Devoti et al, 2017;focal mechanisms, Totaro et al, 2016, Pondrelli et al, 2020; active stress indicators, IPSI database, Mariucci and Montone, 2020) show that the central sector of the Calabrian Arc is characterised by an NW-SE oriented extensional tectonic regime, responsible for large magnitude earthquakes (e.g., Galli and Peronace, 2015). Towards the east, the Ionian offshore area undergoes a transcurrent regime due to the oblique plate convergence (Totaro et al, 2016), and is affected by active compressional structures related to the Calabrian subduction complex (e.g., Polonia et al, 2011;Gutscher et al, 2017).…”

Geodynamic and seismotectonic model of a long-lived transverse structure: The Schio-Vicenza Fault System (NE Italy)

“…The Adriatic plate indenter has been considered as delimited by the Giudicarie fault system to the west, the Pustertal-Gailtal fault to the north (Ratschbacher et al, 1991;Reiter et al, 2018;Rosenberg et al, 2004Rosenberg et al, , 2007 and the Dinaric fault system to the east (Mantovani et al, 2006;Massironi et al, 2006;Heberer et al, 2017;Brancolini et al, 2019). In this context, the SVFS represents an intraplate structure crossing the Mesozoic Trento platform.…”

“…An interesting although complicated model has been proposed by Laubscher (1996), who rejects the model of the northern Adria indentation against the eastern Alps (e.g. Ratschbacher et al, 1991). The SVF is interpreted as a boundary of the Veneto foreland, delimiting the structural high called "Adige embayment" (the Lessini Mountains block), separating the central from the eastern Southern Alps, which is defined as kinematically "irksome".…”