Automated moment tensor inversion to estimate source mechanisms of hydraulically induced micro-seismicity in salt rock

Two methods for an automated moment tensor inversion are investigated. The first is a single-source inversion using amplitude spectra of observed body-wave phases and theoretical Green functions, and the second a relative moment tensor inversion using spectral moments of body-wave phases. An optional general-dislocation-source constraint is introduced to stabilize the inversions for sparse data. Both methods are successfully tested on synthetic data and are applied to hydraulically induced micro-seismicity in salt rock. The estimated moment tensors of 187 events show similar radiation patterns with a major double-couple component and a small or zero isotropic component. We explain the double-couple component with failure on horizontal, preexisting planes of weakness within the process zone of circular tension-fractures (C) 1999 Elsevier Science B.V. All rights reserved.