General dislocation model based microseismic focal mechanism inversion in frequency domain

Fracture directionality, scale and stress state of hydraulic fracturing areas are extremely important for the unconventional resources exploration. Their information can be obtained from the study of microseismic focal mechanisms. For microseismic events, double-couple or moment tensor models are usually used in focal mechanism inversion. In this study, we use the “Shear & Tensile” general dislocation model to describe the microseismic source. Based on this model, we develop an approach to calculate microseismic focal mechanism using amplitude spectra fitting and simulated annealing technique in frequency domain. The new method takes account of full waveform information including phase and polarities of first P wave arrivals and can provide dislocation length along each direction as well as common source parameters (strike, dip and rake angles) in the study area. The synthetic tests on surface and borehole network and applications to real data show that our method is robust and efficient.