Ambient Vibrations

In geology and other related disciplines, seismic noise is a generic name for a relatively persistent vibration of the ground, due to a multitude of causes, that is a non-interpretable or unwanted component of signals recorded by seismometers.

Physically, seismic noise consists mostly of surface waves. Low frequency waves (below 1 Hz) are generally called microseisms; high frequency waves (above 1 Hz) are called microtremors. Its causes include nearby human activities (such as traffic or heavy machinery), winds and other atmospheric phenomena, and ocean waves.

Seismic noise is relevant to any discipline that depends on seismology, such as geology, oil exploration, hydrology, and earthquake engineering, and structural health monitoring. It is often called ambient wavefield or ambient vibrations in those disciplines. (However, the latter term may also refer to vibrations transmitted through by air, building, or supporting structures.)

Seismic noise is a nuisance for activities that are sensitive to vibrations, such as accurate measurements, precision milling, telescopes, and crystal growing. On the other hand, seismic noise does have some practical uses, for example to determine the low-strain dynamic properties of civil-engineering structures, such as bridges, buildings, and dams; or to determine the elastic properties of the soil and subsoil in order to draw seismic microzonation maps showing the predicted ground response to earthquakes.

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