Seismic noise is relevant to any discipline that depends on seismology, including geology, oil exploration, hydrology, and earthquake engineering, and structural health monitoring.
Seismic noise is often a nuisance for activities that are sensitive to extraneous vibrations, including earthquake monitoring and research, precision milling, telescopes, gravitational wave detectors, and crystal growing.
Research on the origin of seismic noise[1] indicates that the low frequency part of the spectrum (below 1 Hz) is principally due to natural causes, chiefly ocean waves.
[2][3][4][5] At high frequency (above 1 Hz), seismic noise is mainly produced by human activities such as road traffic and industrial work; but there are also natural sources, including rivers.
[7][8] Anthropogenic noise detected during periods of low seismic activity includes "footquakes" from soccer fans stamping their feet in Cameroon.
[9] Non-anthropogenic activity includes pulses at intervals between 26 and 28 seconds (0.036–0.038 Hz) centered on the Bight of Bonny in the Gulf of Guinea that are thought to be caused by reflected storm waves, focused by the African coast, acting on the relatively shallow sea-floor.
[11] Globally visible 30 s–5 s seismic noise was recognized early in the history of seismology as arising from the oceans, and a comprehensive theory of its generation was published by Longuet-Higgins in 1950.
After the 1933 Long Beach earthquake in California, a large experiment campaign led by D. S. Carder[12] in 1935 recorded and analyzed ambient vibrations in more than 200 buildings.
Interest on ambient vibrations in structures grew further, especially in California and Japan, thanks to the work of earthquake engineers, including G. Housner, D. Hudson, K. Kanai, T. Tanaka, and others.
In the late 1990s, array methods applied to seismic noise data started to yield ground properties in terms of shear waves velocity profiles.
[18][19][20][21] The European Research project SESAME[22] (2004–2006) worked to standardize the use of seismic noise to estimate the amplification of earthquakes by local ground characteristics.
Seismic Interferometry methods, in particular, use correlation-based methods to estimate the seismic impulse (Green's Function) response of the Earth from background noise and have become a major area of application and research with the growth in continuously recorded high quality noise data in a wide variety of settings, ranging from the near surface[29] to the continent scale[30] Like earthquakes, ambient vibrations force into vibrations the civil engineering structures like bridges, buildings or dams.
Single-station methods: The power spectrum computation of ambient vibration recordings in a structure (e.g. at the top floor of a building for larger amplitudes) gives an estimation of its resonance frequencies and eventually its damping ratio.
The COVID-19 pandemic produced a unique situation in which human transportation, industrial, and other activities were significantly curtailed across the world, particularly in densely populated areas.
Therefore, models are needed to compute these observations (dispersion curve, modal shapes...) in a suitable forward problem that can then be compared with the experimental data.
This can be achieved by GPS clock, common start signal using a remote control or the use of a single digitizer allowing the recording of several sensors.