Towards seismic moment tensor inversion for source mechanism

Faranak Mahmoudian and Kristopher A. Innanen

ABSTRACT

The objective of this work is to obtain seismic moment tensor, M pq , from amplitude inversion of multi-component microseismic data. M pq describes source mechanism and can be decomposed into double-couple, isotropic and compensated-linear-vector-dipole (related to tensile fracturing) components - the tensile components might show a correlation to hydrocarbon production rate. The retrieved M pq are sensitive to the accuracy of the source location, the accuracy of the velocity model, and the receiver array geometry. Excluding the first two factors, the determination of the proper observation geometry for which the full moment tensor is resolvable was sought. Having two vertical or surface receiver arrays, or a combination of them, M pq may be fully determined using the inversion of P- and S-wave first arrival amplitudes. This configuration, which is sufficient for this purpose, includes the receiver arrays located in the vertical and horizontal part of a single deviated well. To avoid the cumbersome task of picking first-arrival amplitudes, we considered a waveform inversion scheme based on the method proposed by Vavryčuk and Kühn (2012). This method combines inversions in both the time and frequency domains. The first requirement was the inversion for the source-time function in the frequency domain. Second, a time domain inversion for M pq using the source-time function calculated in the first step was initiated. For this waveform inversion, we have not yet achieved an accurate retrieval of M pq , but we have been able to obtain an accurate source-time function estimate.

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