The Effect Of Media Anisotropy On Inversion Of Moment Tensor

Seismic moment tensors induced by microseismic can reveal the process of hydraulic fractures,which are important to oil and natural gas industry.In the past,it is usually assumed that the propagation media and the source region are isotropic.The moment tensor inverted in this way will be affected by the media anisotropy.In this paper,the effect of media anisotropy on moment tensor inversion is discussed in detail through spectral element method(SEM)forward modeling,least squares inversion and "Cut and Paste"(CAP)inversion.The results show that:(1)the media anisotropy has an effect on the amplitude and arrival time of seismic records,resulting in errors in moment tensor inversion.(2)Considering the variation of seismic arrival time,the moment tensor inversion is less affected by media anisotropy.(3)In the case of uniform distributed geophones,the inversion error is larger when the angle is larger between the main or auxiliary fault plane and the vertical Z-axis.The bigger the angle is,the bigger the error is.The average error of the maximum moment tensor components content is 39.1% in this paper.When the content of explosive source(ISO)component in moment tensor is large,the inversion error is large.When the moment tensor contains the compensated linear dipole source(CLVD)component,the inversion error increases obviously.When the media anisotropic strength is very high,the average error of the components content of the moment tensor inversion increases significantly,the maximum of which is 66.6% in this paper.The results are applied to the actual microseismic events.They show that the media anisotropy of shallow surface generally affects the moment tensor inversion of microseismic events.In the research area of this paper,the average error of the component content of moment tensor is 23.5%.In order to retrieve the seismic moment tensor of actual microseismic events more accurately in the future,the influence of media anisotropy should be considered.