Microseismic Monitoring: Insights from Moment Tensor Inversion

Farshid Forouhideh and David W. Eaton

ABSTRACT

This paper reviews the mathematical tools used for describing microseismic source mechanisms. In addition, based on analysis of synthetic seismograms we develop and evaluate a workflow for inverting source mechanisms (moment tensors). We consider several types of focal mechanisms including double-couple (representative of a slip on a fault) and more complex mechanisms that include tensile forces. Our inversion strategy uses a least-square approach that attempts to fit P- and S-wave amplitudes measured using multicomponent borehole geophone array. An important final step in the inversion process is decomposition of the recovered moment tensor into isotropic, compensated linear vector dipole (CLVD) and double-couple components. These three end member focal mechanisms provide the basis for describing most common classes of microseismic events. Our preliminary inversion tests for noise-free synthetic data suggest that the isotropic component is likely to be the least well-resolved parameter.

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