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  | isbn    = 0-89181-602-X

  | isbn    = 0-89181-602-X

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A regional exploration program to study a large unexplored area in the Colombian Amazon basin was conducted by Amoco Production Company in 1987 and 1988.<ref name=ch16r2>Burgett, W., A., Orange, A., Sigal, R., F., 1992, Integration of MT, seismic, gravity, and magnetic data for reconnaissance of the Colombian Amazon: 54th meeting, European Association of Exploration Geophysicists, Expanded Abstracts, p. 428–499.</ref> This study area was very large [approximately 300,000 km² (115,000 mi²)] and remote with dense jungle cover, rugged terrain, and limited road access.

A regional exploration program to study a large unexplored area in the Colombian [http://http://www.greatestplaces.org/notes/amazon.htm Amazon basin] was conducted by Amoco Production Company in 1987 and 1988.<ref name=ch16r2>Burgett, W., A., Orange, A., Sigal, R., F., 1992, Integration of MT, seismic, gravity, and magnetic data for reconnaissance of the Colombian Amazon: 54th meeting, European Association of Exploration Geophysicists, Expanded Abstracts, p. 428–499.</ref> This study area was very large [approximately 300,000 km² (115,000 mi²)] and remote with dense jungle cover, rugged terrain, and limited road access.

The first phase of the program consisted of 31,700 km (19,700 mi) of airborne gravity and [[magnetics]]. The large-scale structures delineated in these surveys were then further investigated by MT The MT survey was feasible with a light helicopter because the crew was small and equipment was light and compact. Data were collected from 43 sites, with a typical spacing of 10–20 km (6–12 mi).

The first phase of the program consisted of 31,700 km (19,700 mi) of [[Gravity basics|airborne gravity]] and [[magnetics]]. The large-scale structures delineated in these surveys were then further investigated by [[magnetotellurics]] (MT). The MT survey was feasible with a light helicopter because the crew was small and equipment was light and compact. Data were collected from 43 sites, with a typical spacing of 10–20 km (6–12 mi).

==Survey results==

==Survey results==

The MT data clearly delineated a thick sedimentary section with internal units that could be correlated from site to site. Three resistivity “packages” were observed:

The MT data clearly delineated a thick sedimentary section with internal units that could be correlated from site to site. Three resistivity “packages” were observed:

* 40–100 ohm-m (sedimentary)

* 40–100 ohmm (sedimentary)

* 150–250 ohm-m (sedimentary)

* 150–250 ohmm (sedimentary)

* >1000 ohm-m (crystalline basement)

* >1000 ohmm (crystalline basement)

[[:file:applying-magnetotellurics_fig16-5.png|Figure 1]] shows a simulated [[cross section]] in the Amazon basin based on MT data.

[[:file:applying-magnetotellurics_fig16-5.png|Figure 1]] shows a simulated [[cross section]] in the Amazon basin based on MT data.