A Comprehensive Study of Fracture Patterns and Densities in The Geysers Geothermal Reservoir Using Microearthquake Shear-Wave Splitting Tomography Page: 4 of 40
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In the first year of our project, we focused on obtaining all the relevant data for the S-wave
splitting study of the NW Geysers. We ultimately obtained these by visiting LBL and helping
locate and copy the data sets needed for our work. Once we had these data we could being
evaluating them in terms of our original hypothesis that they would contain S-wave splitting that
could be used to orient fractures and measure fracture densities. The results of this effort are
shown below (from Lou et al. 1997).
Geysers Polarization direction
38E 51@ 14
38E 50@G 0
In the second year we use these directions and the time differences between the fast and slow S-
waves to calculate a 3-D map of fracture density. We then identified and measured a large
number of split S-wave time differences for different parts of the reservoir volume. These
measurements are then inverted using back-projection tomography to locate the spatial
distribution of crack density. Standard tomographic display methods were then used to create
maps of crack density for characterization and development of the reservoir. The full theory and
methods behind crack-density mapping using shear-wave splitting tomography are given in
Malin, 1993; Lou and Rial, 1994; Shalev and Lou, 1995, Lou et al., 1997; Shalev et al., 1998;
and in a forthcoming publication that we are currently preparing (Malin and Shalev, in prep.). A
sample cross section in the Geysers area is given below (Figure 5 from Malin and Shalev, 1999).
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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/m1/4/: accessed April 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.