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Sensing the voids underground.

Sensing the voids underground

Geoscientists and engineers sometimes need to know if there are cavities buried in the ground. Forgotten shafts left in old coal and salt mines, for example, could collapse and damage overlying buildings if they are not filled in. One method used to detect underground voids is called electrotelluric sounding. This technique exploits the fact that an electric field penetrates into the earth to depths that depend on the field's frequency and the electrical resistivity of the ground. Because a cavity has ahigher resistivity than the surrounding soils, its location and dimensions can be measured by monitoring the frequencies of naturally occurring electric fields that travel into the ground.

Recently Arnon Sugar, Michael Birkos and their colleagues at Geophysics International in Dallas demonstrated that electrotelluric sounding is a useful tool for archaeologists, who consider underground tunnels and caverns buried treasures. With the technique, the researchers were able to detect a 7-meter-high cavity in the tomb of the Ming dynasty Emperor Wan Li, who died in 1620. This tomb is part of a larger network of buried chambers, tunnels and tombs of 13 Ming emperors located near Beijing. Wan Li's tomb is the only one in this network that has been excavated. Sugar says the group plans to go to Guatemala in a few months to help archaeologists hunt for a system of tunnels made by the Maya.
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Title Annotation:electrotelluric sounding used in archaeology
Author:Weisburd, Stefi
Publication:Science News
Date:Nov 22, 1986
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