Focal mechanism and moment tensor in orthorhombic anisotropic media
【Abstract】Hydraulic fracturing zones have anisotropic characteristics on the whole. It is necessary to analyze the influences of anisotropic parameters on focal mechanism and moment tensor. This paper studies the shear–tensile focal mechanism and seismic moment tensor when the source is located in anisotropic media. It analyzes the influences of focal anisotropy on double couple (DC) components, compensated linear vector dipole (CLVD) components, and isotropic (ISO) components. The seismic response characteristics of dry and saturated orthorhombic anisotropy media are also analyzed. The effects of crack parameters and fluid parameters on seismic response are discussed. The following results are obtained based on our research. A. The moment tensor in anisotropic media can be obtained by anisotropic parameters and source quantity. B. The non-DC components caused by shear–tensile crack depend on the rupture mode, type of anisotropic media, crack parameter and section strike. High ISO components appear in dry cracked media and high CLVD components appear in water saturation media. C. Far field P-wave radiation patterns are different between isotropic and anisotropic media. The source characteristics and medium anisotropy have significant impacts on the seismic wave travel time, amplitude, and polarity.
【Keywords】 orthorhombic anisotropy; microseismic; focal mechanism; moment tensor; shear–tensile source;
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