Interpretations of a 3D Seismic Volume, Hawthorne Geothermal Field, Nevada
AuthorKell, Anna Marie
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Hawthorne, Nevada is located in the Walker Lake Domain of the Great Basin, aregion in the western United States known for extensional tectonics and the hightemperature gradients necessary for geothermal power production. Geothermal heatsources include magmatic types and extensional. The extensional type is more commonfor Nevada, where near-surface thermal gradients come from a thinned crust instead offrom volcanism. Extensional systems often do not exhibit surface indicators such assprings or fumaroles; rather, the thermal fluids remain capped below the surface in"blind" systems requiring the need for geophysical exploration. Heterogeneouscompositions and seismic velocities common to geothermal systems create particularseismic imaging difficulties because simplifying assumptions about velocity gradientscannot be made. A 3d seismic volume collected by the Navy Geothermal ProgramsOffice on the Hawthorne Ammunitions Depot represents a rare opportunity to examinethe range of geologic interpretations that can exist on seismic data in the Great Basin.Strong reflection events within the volume project to a ~20 degree dip, allowing thepossibility of a low angle normal fault; while bedding offsets could be interpreted as aseries of steep basinward step faults. Synclines in vertical sections correspond toconcentric circles in horizontal sections, not only raising questions about the possibilityof migration processing artifacts, but also present similarities to sill intrusions as seen inmarine 3d data. This paper explores the seismic evidence for a range of structuralinterpretations.