Seismic Source Mechanism Estimation in 3D Elastic Media

Abstract

We recently developed a novel method based upon reciprocity principles to estimate seismic moment tensor estimation of localized induced and natural seismicity arising in 3D heterogeneous media. The method finds the optimal event location and corresponding moment tensor estimates. Because the method uses an exhaustive search of the 3D media it is globally convergent. It does not suffer from local minima realization observed with local optimization methods, including Newton, Gauss-Newton or gradient descent algorithms. The computational efficiency of our scheme is derived from the reciprocity principle, where the number of 3D model realizations corresponds to the number of measurement detectors. 3D forward modeling is carried out in the damped Fourier domain with the 3D finite-difference code that generates P- and S-waves from the point sources defined by second-order moment tensors. We present results of testing this new FWI moment tensor methodology on the synthetic data for the Raft River geothermal field, Idaho, as well as demonstrate its applicability in designing optimal borehole monitoring arrays in the SIGMA-V fracking experiment at the Homestake Mine, South Dakota. The SIGMA-V experiment seeks to better understand the relationship between stress, seismicity and permeability enhancement in order to advance enhance geothermal system development.