They're using a vibrating trailer to send sound waves as deep as a mile underground. The echoes are recorded to create a picture similar to a medical sonogram. The picture may show shallow faults that could cause earthquakes.
The scientists say the vibrations are harmless and can't be felt except by those standing near the trailer.
The three-day survey continues through Sunday along a mile-and-a-half stretch of roads -- E. Baldwin and W. Shannon Avenues.
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