Magnetotelluric investigations at the Roosevelt Hot Springs KGRA and Mineral Mountains, Utah. Topical report 78-1701. a. 6. 1

Technical Report · Sun Jan 01 04:00:00 EST 1978

DOI:https://doi.org/10.2172/6766105· OSTI ID:6766105

Wannamaker, P

Twenty-five magnetotelluric (MT) sites were monitored. Amongst other MT functions, the transverse electric (TE) and transverse magnetic (TM) apparent resistivity and impedance phase data were provided for the frequency range 3 x 10/sup -3/ Hz to 100 Hz. Some one-dimensional inversion results for this area yielded very low values of estimated true resistivity. Such values are unrealistic in light of established notions about conductivity mechanisms in earth materials. Furthermore, the assembly of such inversions to form a crude two-dimensional model has yielded a calculated 2-D pseudosection far removed from the observed pseudosection. Trial-and-error modeling has provided a better fit although strong differences between observed and modeled data remain and cannot be overcome by any purely two-dimensional model. The most noteworthy difficulty is the presence of exaggerated contrasts in apparent resistivity persisting to the lowest frequency of observation for both modes of wave excitation. Single-conductor, 2-D, TE and TM modeling may explain such problems in terms of three-dimensional effects. Electrical strike estimation may be a meaningless endeavour in a strongly three-dimensional area. The total fields do not decompose into the standard principal modes (TE and TM) and H/sub z/ depends on horizontal derivatives of both electric field components. Multiple symmetry axes result in multiple estimated strike directions depending upon wherethe observer is located. When derivatives of electric field are relatively small, noise may be the determining factor. The estimated strike directions for the Roosevelt stations are, however, quite consistent. The elongate resistive horst structure of the Mineral Mts. situated in conductive valley fill is felt to be the overwhelming reason for such a consistency.

• Research Organization: Geotronics Corp., Austin, TX (USA)
• OSTI ID: 6766105
• Report Number(s): TID-28690
• Country of Publication: United States
• Language: English

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