Ambient noise seismology

Ambient noise seismology uses continuous background vibrations recorded at seismic stations to estimate wave propagation and image Earth’s subsurface without relying on earthquakes or explosions.

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Seismic interferometry: A method that extracts information about wave propagation between sensors by combining recorded wavefields. Ambient-noise processing uses interferometric correlations to recover signals between seismic stations.
Seismic noise: Ground motion recorded by seismometers that is not attributed to a target earthquake signal. Ambient noise seismology treats this otherwise unwanted motion as its data source.
Seismic tomography: An imaging method that infers Earth's internal structure from seismic-wave observations. Ambient-noise measurements provide an earthquake-independent input to seismic imaging.
Active-source seismology: Seismic imaging that uses controlled sources such as explosions or vibrators to generate waves. It offers deliberate source control, while ambient-noise seismology uses naturally occurring vibrations.
Cross-correlation: A measure of similarity between two signals as one is shifted in time relative to the other. Correlating station records produces the signal used to estimate waves traveling between them.
Microseism: A continuous seismic signal generated mainly by ocean-wave interactions and recorded across broad regions. Ocean-generated microseisms are a major source of the vibrations used in ambient-noise studies.
Volcano seismology: The study of seismic signals and subsurface processes at volcanoes. Continuous noise correlations can monitor changing wave speeds beneath volcanic systems.
Earthquake seismology: The study of earthquakes and the seismic waves they generate. Ambient-noise methods can estimate wave structure where suitable earthquake signals are unavailable.
Green's function: A system’s response at one location to an idealized impulse applied at another. The correlated noise can approximate the seismic Green’s function between two stations.
Seismometer: An instrument that measures ground motion over time. The method depends on synchronized records from multiple seismometers.