A Comprehensive Study of Fracture Patterns and Densities in The Geysers Geothermal Reservoir Using Microearthquake Shear-Wave Splitting Tomography Page: 3 of 40
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4. Comparison of the Accomplishments with Goals and Objectives
For this project our original Goals and Objectives were:
1. S-wave splitting identification and processing of microearthquake recordings from
geothermal exploration and production areas. Application of this identification and
processing approach to the NW Geysers
2. Determining the crack orientations around the seismic networks, past and present, in
the NW Geysers.
3. Complete a 3-D inversion for the crack density distribution in the NW Geysers.
4. Develop further the computational methods for forward modeling of anisotropic wave
5. Develop a software package that can handle all of the steps above.
The Accomplishments in each of these areas of our project were:
1. We both tested the S-wave splitting analysis approaches of the University of
Edinburgh group (S. Crampin, PI) and developed our own method. The new methods
are summarized in Lou et al. (1997), a copy of which is attached to this Final Report.
2. We analyzed several thousand S-waves at the NW Geysers using the past and present
seismic networks there. In these data we identified the S-wave splitting and mapped
its directions. These results are contained in Lou et al. (1997). .
3. Using the orientations and splitting times found in Goal 2, we completed an fracture
orientation constrained inversion of the S-wave splitting times for crack density. This
was done using a tomographic back projection method. The results are discussed in
Malin and Shalev (1999), a copy of which is attached to this Final Report.
4. We met with limited success in improving the forward computation of S-wave splitting
in realistic geological materials. After communication with several other groups
working in this same area, we concluded that a brute force method such as Finite
Elements would probably be the best way to proceed. We are continuing this
development on a step-by-step basis, but have found the going slow. This was the
least successful undertaking of our project goals.
5. The software package we developed for Goals 1 to 3 above is attached here and has
been used by the geothermal companies in California and Kenya..
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Malin, Peter E.; Shalev, Eylon; Lou, Min; Simiyu, Silas M.; Stroujkova, Anastasia & McCausland, Windy. A Comprehensive Study of Fracture Patterns and Densities in The Geysers Geothermal Reservoir Using Microearthquake Shear-Wave Splitting Tomography, report, February 24, 2004; United States. (https://digital.library.unt.edu/ark:/67531/metadc779483/m1/3/: accessed April 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.