GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.1 GNGTS 2024 Estmatng the source parameters of a moderate earthquake using the second seismic moments A.Cuius 1,2 , A. Saraò 3 , H. Meng 4 , G. Costa 1 1 Department of Mathematcs and Geosciences, University of Trieste, Trieste, Italy 2 Natonal Insttute of Geophysics and Volcanology, INGV, Roma, Italy 3 Natonal Insttute of Geophysics and Applied Geophysics, OGS, Trieste, Italy 4 Department of Earth and Space Sciences, Southern University of Science and Technology, Shenzhen, Guangdong, China Introducton The study of earthquake generaton and associated seismic parameters such as seismic moment, rupture size, rupture velocity and directon, and stress drop is crucial for understanding earthquake dynamics and the underlying physics of the seismic process. This informaton plays an important role in the estmaton of ground shaking near the earthquake source and in the assessment of seismic hazard, even for low to moderate magnitude earthquakes. The kinematc propertes of small earthquakes are ofen difcult to determine, and simple models are ofen used to represent these events, although improved records show that source complexity is common even for small earthquake ruptures (e.g. Calderoni and Abercrombie, 2023 and reference therein). A critcal task in determining fnite source atributes for moderate and low magnitude earthquakes requires good removal of path and site efects. To address this problem, several methods based on empirical Green's functon (EGF) deconvoluton have been developed in recent decades. Although the EGF ofers several advantages, its applicaton is associated with some difcultes, as there are ofen no focal mechanisms for small earthquakes and source efects have been observed even for low energy events (Calderoni et al. 2023). The simplest general representaton of an earthquake that contains informaton about the rupture extent and directvity is the point-source representaton plus the variances or second-degree moments of the moment-release distributon. The hypocenter and the origin tme of the earthquake correspond to the spatal and temporal average (frst degree moment) of the release moment distributon. The informaton about the rupture extent, the characteristc duraton and the directon of rupture propagaton correspond to the variance of the moment distributon in the spatal, temporal and spato-temporal domain (second-degree moments). Seismic moments are calculated from apparent duratons measured from apparent source tme functons (ASTF) for each staton afer removal of path efects. The ASTF is thus the projecton of the rupture process onto the seismic ray path, and its propertes also depend on the azimuth and take-of angles (e.g. McGuire, 2004). For a unilateral rupture, the ASTF observed from statons in the directon of propagaton would be signifcantly shorter than the ASTF from statons in the opposite directon.