Resistivity Imaging

A Presentationby

Advanced Geosciences, Inc.

To change picture, left click or wait 15 seconds

Depth PenetrationUsing the Sting/Swift system, resistivity imagingsurveys can be performed to large depths. Thisexample shows measurements down to approxi-mately 200 meters. Data, courtesy of GeologicalSurvey of Austria.

Cave detection

A previously unknown cave, the Sting Cave, was detected with the Sting/Swift system

Cave 1 is a previously known cave. The Sting Cave (Cave 2) was detected during a demonstration survey over Cave 1

The Sting Cave was carefully mapped andnamed by Mike Warton & Associates

Three important lessons can be learned from the Sting Cave example

1. The resistivity imaging technique is “side-looking”

The profile was oriented perpendicularto the screen, and positioned where the entrance hole was drilled. The hole, whichwas drilled into the center of the anomalyalmost missed the cave, which is mainly located to the right of the profile

Three important lessons can be learned from the Sting Cave example

2. The resistivity image may be “distorted” by unknown formations.

The limestone in the area is horizontally layered and less competent layers havebeen eroded under the main cave. Theseeroded layers are less than a meter in thickness, but prevents the current to pass through the rock and thereby magnifies the shape of the cave in the resistivity image.

The Sting Cave appers larger than Cave 1 even though it in reality issmaller.

Three important lessons can be learned from the Sting Cave example

3. The resistivity image is a picture in terms of electrical resistivity and not a true picture as we are used to seeing.

The Sting cave (Cave 2) appears to have higher resistivity (darker grey),even though both caves are air-filled. However, Cave 1 has moiststalactites and stalagmites connecting the roof and the ceiling.Therefore current can pass from theroof to the ceiling and make this caveappear more transparent.

Dipole-dipole electrode array Dipole-dipole gives high resolution,but has the weakest signal.

Schlumberger electrode array

Schlumberger does not have as highresolution as dipole-dipole but has stronger signal.

Wenner electrode arrayWenner has poor lateral resolution, buthas the strongest signal

Conclusion:

• Use the dipole-dipole array when the highest resolution is required

• Use the Schlumberger array in case of electrically noisy conditions which is often the case under low resistive conditions such as landfills and environmental sites

• Use the Wenner array as a last resort, or if you are mapping basically horizontal layers

The profiles above are recorded withthree different arrays, keeping the electrodes in the exact same position

The Sting/Swift system comprises the Sting resistivity meter, the Swift interface box and a number of electrode switches.

The switches are simply “rubberbanded” to the electrode stakes

Easy and simpleto set up and run.

Resistivity survey at the Amistad Dam

The survey was performed along the embankment on the bottom of the almost dry dam

The dam is leaking under the embankment in the karstic limestone.

One of more than 15 concrete plugged holes, where water leaked out of the dam.

Landfill Survey using the Sting/Swift automatic resistivity system, courtesy of SAIC, Middletown Pennsylvania

Site investigation for proposed tunnel, courtesy of Hyundai Construction Company, Korea

Resistivity/GPR survey at historical tree site in El Paso, Texas

Objective: to map the root system

Pole-pole 3D command fileIt is easy to create a pole-pole 3D command file by using the “Create command file” option in the UserLoad software

3D resistivity image Survey (pole-pole) performed over a horizontally layered limestone. Displayed high resistive area is caused by unknown structure within the limestone.

3D presentation, courtesy of “C Tech Development Corp.”

Shallow marine resistivity survey

Four Wenner (a=6m) profiles repeated along the same line

Trawling Data

0.36

0.37

0.38

0.39

0.40

0.41

0.42

0:00:00 0:00:17 0:00:35 0:00:52 0:01:09 0:01:26 0:01:44 0:02:01 0:02:18

Time from passing start marker

App.

Res.

(ohm-

meter

)

Series1

Series2

Series3

Series4

Trawling data

Time from passing the start marker

If you would like to get more information on the electrical resistivity imaging technique or our Sting/Swift, automatic resistivity imaging instrument you can contact us at:

Advanced Geosciences, Inc.10710 D-K Ranch Rd.Austin, Texas 78759USA

Phone +1 512 335-3338Fax +1 512 258-9958

E-mail agi@agiusa.comWeb site http://www.agiusa.com