exploration, geophysical—Geophysical methods have been used to determine the presence and location of solid rock foundations and to classify soils and other underlying strata with respect to their relative degrees of compaction. One method is based on the electric resistivity of different layers of soil. Another method depends on differences in the speed of propagation of impulses that may be produced by an explosion or by a continuous vibration of known frequency.

–

Source: NSPS “Definitions of Surveying and Related Terms“, used with permission.

Part of LearnCST’s exam text bundle.