| Title | Geophysical Delineation of the Crater Bench, Utah, Geothermal System |
|---|---|
| Authors | Hardwick, Christian L.; Chapman, David S. |
| Year | 2011 |
| Conference | Geothermal Resources Council Transactions |
| Keywords | Geothermal; Exploration; Geophysics; Gravity; Magnetotellurics; Crater Bench; Abraham Hot Springs; Baker Hot Springs; Crater Hot Springs; Fumarole Butte |
| Abstract | Crater Bench, the site of Utah’s most active thermal spring system is situated in west-central Utah within the Basin and Range province of western North America. With flow estimates of 5400 and 8400 lpm and temperatures of up to 87 °C, minimum thermal output is estimated at 20 MW. However, the geothermal system is poorly understood with little constraint on subsurface extent and capacity. We report on geophysical surveys leading to a drilling program aimed at correcting these deficiencies. Previous work done in the area of Crater Bench includes aeromagnetic, dipoledipole resistivity and limited gravity surveys. In the summer of 2010, we added 50 magnetotelluric (MT) stations and 88 new gravity stations. 2D MT modeling shows a lens-shaped conductor 300 to 500 m thick overlying an area of low resistivity (10 to 60 ohm?m) directly below the Crater Bench basalt flows as well as depth-to-basement estimates of 1.3 to 3.6 km. The complete Bouguer anomaly map indicates a 20 km by 10 km mass excess centered at Abraham Hot Springs (AHS) on the eastern margin of Crater Bench. Results of 2D gravity modeling provide depth-tobasement estimates of 1.5 km (above the gravity high) to 3.4 km (adjacent gravity-low areas). Modeling results of MT and gravity data correlate well and the prevalent deep structure is interpreted as a horst block, that may facilitate an upflow zone for the hot springs. A volcanic heat source is not indicated by MT modeling though it may still be a minor component in a deep-circulation geothermal system. Our predictions will be tested by drilling at the site in the summer of 2011. Geophysical surveys are an effective, practical and non-invasive approach to delineating subsurface controls and characterizing geothermal systems. |