GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.1 GNGTS 2024 A major advantage of the second moments method is that it can theoretcally be applied to all earthquakes, regardless of their magnitude and complexity, and without requiring the assumptons of an a priori source model (e.g. McGuire 2004; Meng et al., 2020; Cuius et al., 2023). It is also a consistent tool for evaluatng scaling relatonships between fnite source atributes and earthquake magnitudes for large and small earthquakes and for resolving fault plane ambiguity. However, the eliminaton of the path efect is crucial, and a biased ASTF calculaton would lead to inaccurate calculatons of the second seismic moments. However, there may also be other factors that infuence the results of the second moments, even if the propagaton efects have been correctly removed. The aim of this study is to implement and test an efcient method for estmatng source parameters and rupture directvity in near real-tme for medium and small earthquakes. To achieve our goal, we implemented an approach developed by McGuire et al. (2004), which consists of calculatng the second-degree seismic moments (Meng et al., 2020; Cuius et al., 2023). In this paper, we frst perform a study with some synthetc tests to evaluate the infuence of uncertaintes related to our prior knowledge and observatons on the resultng source parameters (Cuius et al. 2023). We then apply the method to a real earthquake in Italy and present the result. Analysis of the sensitvity of the second moments tensor resolutons To evaluate the sensitvity of the second moment solutons, we used synthetc ASTFs computed for a rectangular plane fault discretzed by a grid of cells, each assigned a specifc slip value. Full details can be found in Cuius et al. 2023. The input parameters used to model the ASTF for a magnitude Mw 4.6 earthquake source are listed in Tab. 1. We assumed that the epicenter was located in central Italy and approximated the fault as a 3.0 km box model (Fig. 1). The rupture area was divided into 12x12 cells, and the slip distributon and rupture tme for the unilateral (Fig. 1a; 1b) and bilateral (Fig. 1d; 1e) scenarios were taken from a previous study of a similar magnitude earthquake (SRCMOD database - Mai and Thinbgaijam, 2014), with a focal mechanism of 247° strike, 46° dip and 40° dip. Using the actual staton confguraton, we calculated the ASTFs with a sampling frequency of 100 Hz and a source tme functon of 3 seconds. A uniform propagaton of the rupture front with a rupture velocity of 2.75 km/s was assumed, which corresponds to 0.9 tmes the S-wave velocity in the source region. A simplifed 1-D velocity model for central Italy was used to model the ASTF (Cuius et al., 2023). Tab. 1. Input parameters used to model the unilateral and bilateral scenarios for the characteristc rupture size ( and ), characteristc rupture duraton ( ), centroid rupture velocity ( ) and directvity (dir). Unilateral rupture Bilateral rupture (km) (km) (sec) | (km/s) Dir (km) (km) (sec) | (km/s) Dir I n p u t parameters 1.39 1.21 0.42 2.64 0.80 1.39 1.21 0.31 1.13 0.25