Šílený, Jan (2018) Constrained Moment Tensors: Source Models and Case Studies. In: Moment Tensor Solutions. Springer Natural Hazards . Springer Verlag, pp. 213-231. ISBN 978-3-319-77359-9
Full text not available from this repository.Abstract
In recent decades, the earthquake mechanism, regardless of scale, has commonly come to be described by the moment tensor (MT). The MT has been used when inverting local but, especially, teleseismic (Global CMT project: Dziewonski et al. 1981; Ekstrom et al. 2012; USGS: Sipkin 1982; Sipkin and Zirbes 2004; ERI: Kawakatsu 1995) and regional (e.g., Dreger and Helmberger 1993; Ritsema and Lay 1993; Nábělek and Xia 1995; Braunmiller et al. 2002; Pondrelli et al. 2002; Stich et al. 2003; Kubo et al. 2002) data. For local data, here, I cite events occurring within earthquake swarms (Jakobsdóttir et al. 2008; Horálek and Fischer 2008). The unconstrained MT is the most comprehensive description of shear and non-shear sources and is the body force equivalent of a rupture (i.e. it consists of a system of forces, in fact, force couples) that generates the same wave field in a continuous medium as an actual rupture. In this way, it is not a physical source but substitutes for real processes occurring within the focus. As a system of body forces, the MT is not a priori convenient for offering a simple perception of an earthquake focus. Therefore, for the sake of interpretation, the MT is generally decomposed into simple sources. The method of decomposition is not unique. The most commonly and widely used procedure is one that splits the general MT into isotropic and deviatoric portions (unique), and then splits the deviatoric portion into a double couple (DC) and a compensated linear vector dipole (CLVD) with a common major tension or pressure axis (ambiguous). The somewhat painful procedure of searching for a reasonable decomposition amongst a theoretically infinite number of processes is described in Julian et al. (1998). The MT captures general combinations of dipoles and, as such, is able to approach a wide class of mechanisms that can occur within an earthquake source. An important advantage of the MT description is a linear relationship between source parameters and seismic observations (through the response of a medium, Green’s function) that implies linearity for the inversion task. As such, the MT allows fast and unique retrieval of the six independent parameters—M11, M12, M13, M22, M23, and M33—without the need to specify an initial guess. The MT is not only the most general description of a mechanism relevant to an earthquake source. In general, it is also relevant to the fracturing of a solid body, including all of the modes of fracturing recognized within fracture mechanics and their combinations. However, the MT also includes mechanisms that do not generally represent realistic physical sources because it does not describe the rupture itself but rather body force equivalents of actual rupturing. As such, the MT is needlessly general. In addition to rupture mode I (tensile fracturing), rupture modes II and III (plane and anti-plane shear slip), combinations of force systems that do not correspond to a physically feasible rupturing are also present. Therefore, for the simple rupturing expected within the foci of tectonic earthquakes, the MT is unnecessarily complex, leading to more parameters than those relevant to simple rupture models.
| Item Type: | Book Section |
|---|---|
| Application references: | Mechanism: Shear-Tensile Crack |
| Subjects: | Methodology > Method and procesing > Source parameter estimation |
| Project: | EPOS-IP |