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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. == Causes == Research on the origin of seismic noise〔 S. Bonnefoy-Claudet, F. Cotton, and P.-Y. Bard (2006), ''The nature of noise wavefield and its applications for site effects studies. A literature review.'' Earth Science Review, volume 79, pages 205–227. 〕 indicates that the low frequency part of the spectrum (below 1 Hz) is due to natural causes, chiefly ocean waves. In particular the peak between 0.1 and 0.3 Hz is clearly associated with the interaction of water waves of nearly equal frequencies but opposite directions.〔 M. S. Longuet-Higgins (1950). ''A theory of the origin of microseisms.'' Philosophical Transactions of the Royal Society of London, Series A, volume 243, pages 1–35. 〕〔 K. Hasselmann (1963), ''A statistical analysis of the generation of micro-seisms.'' Review of Geophysics, volume 1, issue 2, pages 177–210. 〕〔 S. Kedar, M. Longuet-Higgins, F. W. N. Graham, R. Clayton, and C. Jones (2008). ''The origin of deep ocean microseisms in the north Atlantic ocean.'' Proceedings of the Royal Society of London, series A, pages 1–35.〕〔 F. Ardhuin, E. Stutzmann, M. Schimmel, and A. Mangeney (2011), ''Ocean wave sources of seismic noise.'' Journal of Geophysics Research, volume 115. 〕 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, like rivers. Around 1 Hz, wind and other atmospheric phenomena are also a major source of ground vibrations. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Seismic noise」の詳細全文を読む スポンサード リンク
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