基于"剪切+张裂"一般位错模型频率域求解微震震源机制

Fracture directionality, scale and stress state of hydraulic fracturing areas are extremely important for the exploration of unconventional oil and gas resources. These 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, a "Shear & Tensile" general dislocation point model is presented to describe the source of microearthquakes. 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. We also find that shear and tensile dislocation lengths are independent of stress drop and can be used as new parameters for quantitative evaluation of hydraulic fracturing.