Comparison of the seismic and ground probing radar methods in geological surveying

Abstract

The use of ground probing radar has increased significantly over the past few years in the civil engineering field. As a geophysical technique it has much in common with the seismic reflection method. The information derived from both methods is displayed as a time/distance cross-section, which is very similar in appearance to a geological cross-section. However, the time section can only be converted to a depth section when the velocity of propagation of the seismic or electromagnetic pulse within each of the resolved layers is known. The use of these two methods in shallow geological surveys at the site investigation stage of a civil engineering construction is reviewed and illustrated by case histories. It is shown that the development of high-frequency sources has improved the resolution obtainable from the seismic reflection method while the gradual improvement in instrumentation has resulted in greater penetration being achieved with the radar method. A consideration of the penetration shows that with both methods it is largely controlled by the moisture content of the superficial deposits, which has a very strong influence on the attenuation of both seismic and electromagnetic energy. The effect is, in fact, complementary since a dry material will transmit electromagnetic energy better than a saturated one, while the converse is true for seismic energy.