Changes

  | part    = Predicting the occurrence of oil and gas traps

  | part    = Predicting the occurrence of oil and gas traps

  | chapter = Applying magnetotellurics

  | chapter = Applying magnetotellurics

  | frompg  = 16-1

  | frompg  = 16-10

  | topg    = 16-12

  | topg    = 16-10

  | author  = Arnie Ostrander

  | author  = Arnie Ostrander

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch16/ch16.htm

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch16/ch16.htm

  | isbn    = 0-89181-602-X

  | isbn    = 0-89181-602-X

}}

}}

MT can be used in an overthrust environment to delineate conductive sediments beneath a resistive thrust plate. It is often difficult to acquire good-quality seismic data in an overthrust area where high-velocity (high-resistivity) rocks overlie low-velocity (low-resistivity) sediments.

Magnetotellurics (MT) can be used in an [[overthrust]] environment to delineate [[Wikipedia:Electrical resistivity and conductivity|conductive]] sediments beneath a [[Wikipedia:Electrical resistivity and conductivity|resistive]] thrust plate. It is often difficult to acquire good-quality [[seismic data]] in an overthrust area where high-velocity (high-resistivity, low-conductivity) rocks overlie low-velocity (low-resistivity, high-conductivity) sediments.

The Precambrian overthrust in the Bear Springs area of northwestern Colorado is an example.<ref name=ch16r5>Mills, A., 1994, Zephyr Geophysical Services, personal communication.</ref>

The [[Precambrian]] overthrust in the Bear Springs area of northwestern Colorado is an example.<ref name=ch16r5>Mills, A., 1994, Zephyr Geophysical Services, personal communication.</ref>

==Survey results==

==Survey results==

[[file:applying-magnetotellurics_fig16-7.png|thumb|{{figure number|1}}An 11-station MT profile across the thrust. Drafted from data from Mills.<ref name=ch16r5 />]]

[[file:applying-magnetotellurics_fig16-7.png|thumb|500px|{{figure number|1}}An 11-station MT profile across the thrust. Drafted from data from Mills.<ref name=ch16r5 />]]

The MT station near the drill hole (see diagram below) shows a thin, near-surface conductor on top of the resistive Precambrian thrust sheet. This is a wedge of Quaternary and [[Tertiary]] sediments. Beneath the thrust, a thick conductive section of Cretaceous sediments is observed.

The MT station near the drill hole (see diagram [[:file:applying-magnetotellurics_fig16-7.png|Figure 1]]) shows a thin, near-surface conductor on top of the resistive Precambrian thrust sheet. This is a wedge of [[Quaternary]] and [[Tertiary]] sediments. Beneath the thrust, a thick conductive section of [[Cretaceous]] sediments is observed.

[[:file:applying-magnetotellurics_fig16-7.png|Figure 1]] below is an 11-station MT profile across the thrust.

[[:file:applying-magnetotellurics_fig16-7.png|Figure 1]] is an 11-station MT profile across the thrust.

==Structural details==

==Structural details==

* Thickness of Precambrian thrust sheet

* Thickness of Precambrian thrust sheet

* Thinning of Cretaceous sediments to the south

* Thinning of Cretaceous sediments to the south

* Depth to top of Paleozoic sediments

* Depth to top of [[Paleozoic]] sediments

* No differentiation between Paleozoic and basement

* No differentiation between Paleozoic and [[basement]]

A very detailed subsurface structural map could be obtained in this area using a 3-D grid, controlled-source MT survey depicting the Precambrian/Cretaceous thrust contact and the top of the Paleozoic section.

A very detailed subsurface structural map could be obtained in this area using a 3-D grid, controlled-source MT survey depicting the Precambrian-Cretaceous thrust contact and the top of the Paleozoic section.

==See also==

==See also==

* [[What is magnetotellurics?]]

* [[Magnetotellurics]]

* [[What does an MT survey measure?]]

* [[Magnetotellurics survey measurements]]

* [[How are MT data acquired?]]

* [[Magnetotelluric data acquisition]]

* [[Case history: frontier basin analysis (Amazon Basin, Colombia)]]

* [[Magnetotellurics case history: frontier basin analysis (Amazon Basin, Colombia)]]

* [[Case history: rugged carbonate terrain (Highlands of Papua New Guinea)]]

* [[Magnetotellurics case history: rugged carbonate terrain (Highlands of Papua New Guinea)]]

* [[Case history: volcanic terrain (Columbia River Plateau)]]

* [[Magnetotellurics case history: volcanic terrain (Columbia River Plateau)]]

==References==

==References==

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Applying magnetotellurics]]

[[Category:Applying magnetotellurics]]