P wave anisotropy, stress, and crack distribution at Coso geothermal field, California

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Journal Article: P wave anisotropy, stress, and crack distribution at Coso geothermal field, California

Abstract
A new inversion method for P wave anisotropy (Wu and Lees, 1999a) has been applied to high-precision, microseismic traveltime data collected at Coso geothermal region, California. Direction-dependent P wave velocity and thus its perturbation, are represented by a symmetric positive definite matrix A instead of a scalar. The resulting anisotropy distribution is used to estimate variations in crack density, stress distribution and permeability within the producing geothermal field. A circular dome-like structure is observed at the southwestern part of the geothermal region southwest of Sugarloaf Mountain. Using a linear stress-bulk modulus relationship, deviatoric stress is estimated to be 3 - 6 MPa at geothermal production depths (1-2 km), assuming all the anisotropy is related to stress. The stress field is compressional NNE-SSW and dilational WNW-ESE, coinciding with a previous, independent study using earthquake focal mechanisms. Following a theory on flat, elliptic cracks, residual crack density estimated from P anisotropy is approximately 0.0078 assuming crack aspect ratios > 1 : 60 and is approximately 0.041 when crack aspect ratios are close to 1:60. Residual crack orientation distribution is related to velocity anisotropy. On the basis of anisotropic part of crack density distribution function, the anisotropic part of permeability distribution may be calculated by a statistical approach via simple parallel fluid flow along cracks.

Authors 
Lees, J.M.; Wu and H.  








Published Journal 
Journal of Geophysical Research, 8/1/1999





DOI 
Not Provided
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Citation

Lees, J.M.; Wu, H.  . 8/1/1999. P wave anisotropy, stress, and crack distribution at Coso geothermal field, California. Journal of Geophysical Research. (!) .


Related Geothermal Exploration Activities
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  1. Coso Geothermal Area
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