Relating Geothermal Resources To Great Basin Tectonics Using Gps
Conference Paper: Relating Geothermal Resources To Great Basin Tectonics Using Gps
AbstractThe Great Basin is characterized by non-magmatic geothermal fields, which we hypothesize are created, sustained, and controlled by active tectonics. In the Great Basin, GPS-measured rates of tectonic "transtensional" (shear plus dilatational) strain rate is correlated with geothermal well temperatures and the locations of known geothermal fields. This has led to a conceptual model in which non-magmatic geothermal systems are controlled by the style of strain, where shear (strike-slip faulting) and extension (normal faulting) both play key roles. Specifically, shear stress is required to continuously fracture fault planes through the entire crust; whereas dilatational stress tends to pull fault planes apart. The combination of shear and dilatation can thus create fluid conduits to great depths, and then sustain them through continued stressing. Furthermore, Basin and Range (B&R) crust must have been thinned by dilatational strain, thus enhancing heat flow from the Moho to the Earth's surface. Assuming the thickness of B&R crust has since achieved dynamic equilibrium, we propose that crustal thickness is sustained by magmatic injection into the lower crust. In late 2003 we discovered such a lower-crustal event beneath Lake Tahoe using GPS, thus confirming this mechanism occurs in the Great Basin. Dilatational stressing of the crust will tend to increase the rate of lower-crustal magmatic events, which can collectively enhance heat flow at depth through advection. Given the higher geothermal favorability where both dilatational and shear strain are present, in the Great Basin this would point to the northern Walker Lane (NW Great Basin) and at the transition between strike-slip and normal faulting regimes in the Central Nevada Seismic belt to the east (e.g., the Stillwater Range), and the zone of strain partitioning adjacent to the Sierran front to the west (e.g., Honey Lake). To further develop this conceptual model for geothermal exploration requires that strain be mapped on the scale of crustal thickness. For this purpose, in 2004 we installed a 60-station GPS network with a spacing of 15-30 km. This network "MAGNET" (Mobile Array of GPS for NEvada Transtension) spans the targeted region of high favorability. By late 2006, strain rates will be of sufficient accuracy for modeling and interpretation. Considering that strain-generating processes might have different characteristic time scales, we plan to model post-seismic visco-elastic relaxation from large 20th century earthquakes in the region, which may dominate the strain rate field in specific areas, including Dixie Valley.
- Geoffrey Blewitt, William C. Hammond and Corne Kreemer
- GRC, 2005
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Geoffrey Blewitt,William C. Hammond,Corne Kreemer. 2005. Relating Geothermal Resources To Great Basin Tectonics Using Gps. In: (!) ; (!) ; (!) . (!) : GRC; p. (!)