Abstract
The decomposition of moment tensors into isotropic (ISO), double-couple (DC) and compensated linear vector dipole (CLVD) components is a tool for classifying and physically interpreting seismic sources. Since an increasing quantity and quality of seismic data allow inverting for accurate moment tensors and interpreting details of the source process, an efficient and physically reasonable decomposition of moment and source tensors is necessary. In this paper, the most common moment tensor decompositions are revisited, new equivalent formulas of the decompositions are derived, suitable norms of the moment tensors are discussed and the properties of commonly used source-type plots are analysed. The Hudson skewed diamond plot is introduced in a much simpler way than originally proposed. It is shown that not only the Hudson plot but also the diamond CLVD–ISO plot and the Riedesel–Jordan plot conserve the uniform distribution probability of moment eigenvalues if the appropriate norm of moment tensors is applied. When analysing moment tensor uncertainties, no source-type plot is clearly preferable. Since the errors in the eigenvectors and eigenvalues of the moment tensors cannot be easily separated, the moment tensor uncertainties project into the source-type plots in a complicated way. As a consequence, the moment tensors with the same uncertainties project into clusters of a different size. In case of an anisotropic focal area, the complexity of moment tensors of earthquakes prevents their direct interpretation, and the decomposition of moment tensors must be substituted by that of the source tensors.
Highlights
The moment tensor describes equivalent body forces acting at a seismic point source (Burridge and Knopoff 1964) and is a basic quantity evaluated for earthquakes on all scales from acoustic emissions to large devastating earthquakes
An explosion is an obvious example of a non-DC source, but non-DC components can be produced by the collapse of a cavity in mines (Rudajev and Šílený 1985; Šílený and Milev 2008), by shear faulting on a nonplanar fault (Sipkin 1986), by tensile faulting induced by fluid injection in geothermal or volcanic areas (Ross et al 1996; Julian et al 1997) when the slip vector is inclined from the fault and causes its opening (Vavryčuk 2001, 2011) or by seismic anisotropy in the focal area (Kawasaki and Tanimoto 1981; Vavryčuk 2005; Roessler et al 2004, 2007)
In order to identify which type of seismic source is physically represented by the retrieved moment tensor, Knopoff and Randall (1970) proposed decomposing the moment tensors into three elementary parts: the isotropic (ISO), double-couple (DC) and compensated linear vector dipole (CLVD) components
Summary
The moment tensor describes equivalent body forces acting at a seismic point source (Burridge and Knopoff 1964) and is a basic quantity evaluated for earthquakes on all scales from acoustic emissions to large devastating earthquakes. In order to identify which type of seismic source is physically represented by the retrieved moment tensor, Knopoff and Randall (1970) proposed decomposing the moment tensors into three elementary parts: the isotropic (ISO), double-couple (DC) and compensated linear vector dipole (CLVD) components. Since an increasing quantity and quality of seismic data allow inverting for accurate moment tensors and interpreting the details of the source process, an efficient and physically reasonable decomposition of moment tensors is necessary This has recently motivated several authors to revisit the existing decompositions (Chapman and Leaney 2012; Zhu and Ben-Zion 2013) and sourcetype plots (Chapman and Leaney 2012; Tape and Tape 2012a, b) and to develop their modifications. I show differences in moment and source tensors ( called the potency tensors) and point out the significance of the source tensor decomposition for earthquake source interpretations in anisotropic media
Sign-in/Register to view highlights & summary 
Published Version (
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