Properties of moment tensors of sources in anisotropic media

Vaclav Vavrycuk


Seismic sources in anisotropic media have more complicated moment tensors than in isotropic media. Planar shear sources produce pure double-couple (DC) moment tensors in isotropy, but generally non-double-couple (non-DC) moment tensors in anisotropy. The non-DC components can comprise both the isotropic (ISO) and compensated linear vector dipole (CLVD) components. The amount of the ISO and CLVD depends on the orientation, strength and symmetry of anisotropy. Shear sources generate no non-DC components in anisotropy, provided that shear faulting is situated in symmetry planes of orthorhombic or higher anisotropy symmetries. The fault plane solution, i.e. the orientation of the fault normal and the slip direction, can be retrieved from a moment tensor and elastic parameters describing anisotropy. Numerical modelling on media with aligned dry or water-filled penny shaped cracks shows that shear faulting generates non-DC components with the percentage comparable with strength of anisotropy. The medium with water-filled cracks produces almost no ISO components. The focal mechanisms seem to be less sensitive to anisotropy than the percentages of the non-DC components.

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In: Seismic Waves in Complex 3-D Structures, Report 14, pp. 203-223, Dep. Geophys., Charles Univ., Prague, 2004.
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