What Does Low Frequency Seismic Energy Mean?
Low-frequency seismic energy is the seismic energy generated in the low-frequency range of 1 to 10 Hz. While conducting seismic refraction survey, low-frequency seismic energy is produced by a seismic source on the surface such as a hammer plate, buffalo gun or weight drop, depending on the depth of penetration required and prevalent site conditions.
Seismic refraction is one of the methods of geophysics used to investigate subsurface ground conditions for trenchless operations. It utilizes seismic waves sourced from the ground surface.
Trenchlesspedia Explains Low Frequency Seismic Energy
The velocity of seismic waves depends on density elastic moduli. The data obtained by seismic refraction is processed to interpret and produce models of seismic velocity and layer thickness of sub-surface ground structures. As the seismic waves propagate downward, they are reflected or refracted off layers in the subsurface and picked up by geophones.
Since the earth absorbs high-frequency energy more readily than it does low-frequency energy waves, most refraction geophones are made to have a natural frequency of 4 cycles/ second. Low-frequency systems can also help find large cavities, such as mines and caves using electromagnetic resistivity test.
Three-dimensional electromagnetic resistivity surveys can be used to produce high-resolution images of subsurface zones and geologic features.