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.
Highlights
The determination of the style of faulting in seismicity models for probabilistic seismic hazard assessment (PSHA) represents the key ingredient to define the orientation and the kinematics of the seismic source
We started by applying a traditional Kostrov method (Kostrov, 1974), in which the sum of the moment tensor elements Mij is taken for all of the Nev earthquakes located within the volume V, obtaining a cumulative seismic moment tensor representative of the seismic deformation occurring within V
– the median of the angular distance between the P, T, B axes (Table 2) as a measure of data input dispersion. The value of these parameters has been used to apply the following decision-making process, sketched in Fig. 5: a. in areas where no focal planes were available, we parameterized the less informative solution given by an equal contribution of normal, reverse, and strike-slip tectonic styles by adopting a uniform distribution of geometries in the space, defining a 100 % random source; b. if more than one event of the same tectonic style is located in an area, we identified the nodal planes and their contributions in terms of seismic moment M0
Summary
The determination of the style of faulting in seismicity models for probabilistic seismic hazard assessment (PSHA) represents the key ingredient to define the orientation and the kinematics of the seismic source. According to Bindi et al (2011), in the case of the Italian strong motion data, the main differences in the ground motion result from the medium- to short-period range (T < 1 s) wherein the expected values for a reverse mechanism are significantly larger than those produced by other styles of faulting. In the case of a normal fault with Mw 6.3, the GMPE by Bindi et al (2011) shows that increasing the distance from 20 to 30 km reduces the mean expected peak ground acceleration (PGA) by about 40 %
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
