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  = 16-11

  | topg    = 16-12

  | topg    = 16-11

  | 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

}}

}}

Seismic methods do not work well in areas covered by volcanics because of the dispersive nature of the volcanics and because of the decrease in acoustic velocity at the base of the volcanics.

[[Seismic data|Seismic methods]] do not work well in areas covered by [[volcanics]] because of the dispersive nature of the volcanics and because of the decrease in [[acoustic velocity]] at the base of the volcanics.

Volcanic terrain, however, is an ideal environment for MT because it is a simple, three-layer stratigraphic package: resistive basalts over conductive sediments, which in turn overlie resistive metamorphic or granitic basement rocks.

Volcanic terrain, however, is an ideal environment for magnetotelluric (MT) surveys because it is a simple, three-layer stratigraphic package: resistive [[basalt]]s over conductive sediments, which in turn overlie resistive [[Metamorphic rock|metamorphic]] or [[Granite|granitic]] [[basement]] rocks.

==Survey results==

==Survey results==

[[file:applying-magnetotellurics_fig16-8.png|thumb|{{figure number|1}}13-station MT natural source survey profile. Drafted from data from Mills.<ref name=ch16r5>Mills, A., 1994, Zephyr Geophysical Services, personal communication.</ref>]]

[[file:applying-magnetotellurics_fig16-8.png|thumb|300px|{{figure number|1}}13-station MT natural source survey profile. Drafted from data from Mills.<ref name=ch16r5>Mills, A., 1994, Zephyr Geophysical Services, personal communication.</ref>]]

[[:file:applying-magnetotellurics_fig16-8.png|Figure 1]] is a 13-station MT natural source survey profile. This east-west section begins near the Idaho-Washington border and extends approximately [[length::75 mi]] (120 km) to the west (Mills, personal communication, 1994).

[[:file:applying-magnetotellurics_fig16-8.png|Figure 1]] is a 13-station MT [[Magnetotelluric data acquisition#Natural-source surveys|natural source survey]] profile. This east-west section begins near the Idaho-Washington border and extends approximately [[length::75 mi]] (120 km) to the west (Mills, personal communication, 1994).

==Structural details==

==Structural details==

These data provided the following structural details:

These data provided the following structural details:

* Considerable variation on the thickness of the volcanics

* Considerable variation in the thickness of the [[volcanics]]

* Considerable variation in the depth to top of basement

* Considerable variation in the depth to top of [[basement]]

* Basalts thin to the east

* [[Basalt]]s thin to the east

* Sediments thin to east and eventually disappear

* Sediments thin to east and eventually disappear

* Basement resistivities are an order-of-magnitude higher on the east end of the profile

* Basement [[Resistivity|resistivities]] are an order-of-magnitude higher on the east end of the profile

Controlled-source MT data could provide 3-D imaging of individual prospects.

[[Magnetotelluric data acquisition#Controlled-source surveys|Controlled-source]] MT data could provide 3-D imaging of individual prospects.

==See also==

==See also==

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

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

[[Category:Applying magnetotellurics]]

[[Category:Applying magnetotellurics]]