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 overlying suffocation of piglets by the sow. The piglets may be weak from illness or malnutrition, the sow may be clumsy or ill, the pen may be inadequate in size or poorly designed so that piglets cannot escape. 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 Electrical resistivity The electrical resistance offered by a homogeneous unit cube of material to the flow of a direct current of uniform density between opposite faces of the cube. of the ground. Because a cavity has ahigher resistivity resistivity Electrical resistance of a conductor of unit cross-sectional area and unit length. The resistivity of a conductor depends on its composition and its temperature. 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 buried treasure - A surprising piece of code found in some program. While usually not wrong, it tends to vary from crufty to bletcherous, and has lain undiscovered only because it was functionally correct, however horrible it is. . With the technique, the researchers were able to detect a 7-meter-high cavity in the tomb of the Ming dynasty Ming dynasty (1368–1644) Chinese dynasty that provided an interval of native rule between eras of Mongol and Manchu dominance. The Ming, one of the most stable but autocratic of dynasties, extended Chinese influence farther than did any other native rulers of China. 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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