A controlled source audiomagnetotelluric investigation of the Ennis Hot Springs Geothermal Area, Ennis, Montana: Final report: Part 2

Technical Report · Wed Jun 01 04:00:00 EDT 1988

DOI:https://doi.org/10.2172/6962296· OSTI ID:6962296

Emilsson, G R

A controlled-source audiomagnetotelluric survey (CSAMT) at the Ennis Hot Springs geothermal area revealed a low resistivity anomaly (3 ohm-m to 10 ohm-m) in the vicinity of the hot springs. The hot springs issue from the base of a gravel terrace on the west side of the Madison Valley. Low apparent resistivities extend to the west under the gravel terrace as well as to the north in an elongated ''plume''. To the southwest the apparent resistivity increases rapidly due to an uplift in the valley basement. One-dimensional inverse modeling in the center of the valley indicates a buried conductive layer probably due to a thick layer of clay-bearing sediments since a nearby test well does not show elevated temperatures. Near the hot springs, one-dimensional inverse modeling did not prove useful, partly because of the two and three-dimensional nature of the structure. Two-dimensional forward modeling near the hot springs provides a more quantitative delineation of the low resistivity zone and of the faulted basement uplifts to the west and south. Details of the structure beneath the conductive zone near the hot springs are difficult to resolve and most of the model control in this region is provided by well logs and seismic data. A technique for correcting data collected in the region close to the transmitter where the plane wave assumption is not valid has derived and has been applied to the low frequency data. 29 refs., 35 figs., 1 tab.

• Research Organization: Montana Coll. of Mineral Science and Technology, Butte (USA). Dept. of Physics and Geophysical Engineering
• DOE Contract Number: FG07-84ID12525
• OSTI ID: 6962296
• Report Number(s): DOE/ID/12525-1-Pt.2; ON: DE88014961
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
29 ENERGY PLANNING, POLICY, AND ECONOMY
DATA
DOCUMENT TYPES
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
EXPLORATION
FEDERAL REGION VIII
GEOLOGIC FAULTS
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
GEOTHERMAL EXPLORATION
GEOTHERMAL RESOURCES
Geothermal Legacy
HOT SPRINGS
INFORMATION
MONTANA
NORTH AMERICA
NUMERICAL DATA
ONE-DIMENSIONAL CALCULATIONS
PHYSICAL PROPERTIES
PROGRESS REPORT
RESOURCES
SEISMIC EFFECTS
THERMAL SPRINGS
TWO-DIMENSIONAL CALCULATIONS
USA
WATER SPRINGS
WELL LOGGING