Application of advanced seismic reflection imaging techniques to mapping permeable zones at Dixie Valley, Nevada. Final technical report
Multifold seismic reflection data from the Dixie Valley geothermal field in Nevada were reprocessed using a nonlinear optimization scheme called simulated annealing to model subsurface acoustic velocities, followed by a pre-stack Kirchhoff migration to produce accurate and detailed depth-migrated images of subsurface structure. In contrast to conventional processing techniques, these methods account for significant lateral variations in velocity and thus have the potential ability to image steeply-dipping faults and fractures that may affect permeability within geothermal fields. The optimization scheme develops two-dimensional velocity models to within 6% of velocities obtained from well and surface geologic data. Only the seismic data (i.e., first arrival times of P waves) are used to construct the velocity models and pre-stack migration images, and no other a priori assumptions are invoked. Velocities obtained by processing individual seismic tracks were integrated to develop a block diagram of velocities to 2.3 km depth within the Dixie Valley geothermal field. Details of the tectonic and stratigraphic structure allowed three dimensional extension of the interpretations of two dimensional data. Interpretations of the processed seismic data are compared with well data, surface mapping, and other geophysical data. The Dixie Valley fault along the southeastern Stillwater Range Piedmont is associated with a pronounced lateral velocity gradient that is interpreted to represent the juxtaposition of relatively low velocity basin-fill strata in the hanging wall against higher velocity crystalline rocks in the footwall. The down-dip geometry of the fault was evaluated by inverting arrival times from a negative move-out event, which we associate with the dipping fault plane, on individual shot gathers for seismic line SRC-3 for the location and depth of the associated reflection points on the fault.
- Research Organization:
- Lettis (William) and Associates, Inc., Walnut Creek, CA (United States); Nevada Univ., Reno, NV (United States)
- Sponsoring Organization:
- USDOE Assistant Secretary for Human Resources and Administration, Washington, DC (United States)
- DOE Contract Number:
- FG07-97ID13465
- OSTI ID:
- 598411
- Report Number(s):
- DOE/ID/13465-T1; ON: DE98005072; TRN: 98:001996
- Resource Relation:
- Other Information: PBD: 18 Feb 1998
- Country of Publication:
- United States
- Language:
- English
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