Preliminary geophysical survey to detect significant shallow voids near Timpson, Texas

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Researchers at the Bureau of Economic Geology, The University of Texas at Austin, noninvasively measured the electrical conductivity and seismic properties of the shallow subsurface at the Dempsey residence near Timpson, Texas. This preliminary survey was completed to determine whether there is geophysical evidence of significant near-surface voids related to historical lignite mining activities. Voids are potentially detectable using several geophysical methods. Mass deficits might be detected using sensitive gravimeters; nonconductive air filling voids in more conductive strata might be detected using resistivity or electromagnetic induction (EM) methods; and air that fills voids might have a lower seismic velocity than the surrounding strata and could be detected with seismic methods. At Timpson, we chose EM in an attempt to identify possible significant voids that reach within about 6 m of the ground surface. We also acquired a test set of seismic data across a known void beneath a concrete pad at the residence to determine whether the void influenced the seismic data enough to be useful in detecting similar unknown voids at this or other similar sites. This report briefly summarizes the results of our investigations.


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