Geoacoustics

a branch of acoustics in which sonic, infrasonic, and ultrasonic phenomena occurring in the earth’s crust are studied. It includes both natural processes (such as the acoustic precursors of earthquakes) and processes associated with the use of elastic waves to study the structure and properties of the upper layers of the earth’s crust (acoustic prospecting, seismic prospecting, deep seismic sounding, and ultrasonic echolocation).

Acoustic prospecting is carried out at a specific frequency, locating foreign ore bodies in massifs between water-filled boreholes by the method of reflection and sounding. Acoustic prospecting began almost simultaneously with hydrolocation and echolocation on the sea bottom. These methods were the first practical application of ultrasound. However, the great absorption of high frequencies (20 kilohertz) in the earth’s crust limits the sounding depth in rock to several dozen meters. At low sonic and infrasonic frequencies the sounding depth is increased, but the possibility of highly detailed study of the section is reduced. Depths of several kilometers can be sounded by utilizing seismic prospecting methods. The structure of layered mediums is also analyzed in greater detail in the boreholes themselves (acoustic logging).