Noise (seismology)

In seismology and seismics , noise describes all random and unwanted signal components that are recorded at a measuring point together with the desired useful signal by the measuring instrument.

Since the seismic waves excited by earthquakes or artificially (e.g. by blasting) usually become very weak with increasing distance, the noise usually has a disruptive effect and hinders the evaluation of the data obtained.

causes

3-component recordings of an earthquake at two neighboring measuring stations: Station KILE (above) has a significantly stronger background noise than station KABE

Seismic waves are registered as vibrations or movements of the ground. Originally, the noise was therefore the ground unrest that is not caused by the source signal. The subsurface is almost always unrest, as every mechanical influence on the soil generates seismic energy. This can happen through natural as well as artificial influences.

Natural sources are e.g. B. Weather conditions: For example, wind can act directly on the ground or it can set high objects (trees, masts, etc.) in vibration , which are transmitted to the ground and thus propagated. However, ground movement also occurs e.g. B. by direct sunlight when the ground or rocks warm and expand.

One of the main sources of natural ground unrest is the sound of the sea, which is generated by waves and surf hitting the coast. But also the tides, air pressure fluctuations or seasonal temperature differences lead to long-period deformations of the ground which trigger correspondingly low-frequency noise.

In addition, there are artificial sources that can be traced back to the influence of humans and technology: vibrations from machines, road or rail traffic, technical devices or people who move a short distance from the measuring instrument. A common source of noise when using explosives to excite signals is e.g. B. the airborne sound, which can be particularly pronounced near the source.

Since seismological measurements today are usually carried out with digital technology, the term noise also includes interference signals that arise from the operation of the measuring device itself (device noise , see also: Noise (physics) ) or from external electromagnetic fields arise. For example, high-voltage lines can influence modern, highly sensitive measuring devices even over several hundred meters.

Individual evidence

^ William M. Telford, Lloyd P. Geldart, Robert E. Sheriff: Applied Geophysics. 2nd edition. Cambridge University Press, Cambridge et al. 1990, ISBN 0-521-33938-3 .
^ ^A ^b Peter M. Shearer: Introduction to Seismology. Cambridge University Press, Cambridge et al. 1999, ISBN 0-521-66953-7 .
↑ Thorne Lay, Terry C. Wallace: Modern Global Seismology (= International Geophysics Series. Vol. 58). Academic Press, New York NY et al. 1995, ISBN 0-12-732870-X .
↑ Peter Bormann (Ed.): New Manual of Seismological Observatory Practice (NMSOP). GeoForschungsZentrum, Potsdam 2002, ISBN 3-9808780-0-7 .
↑ Reinhard Kirsch, Wolfgang Rabbel : Seismic methods in environmental geophysics. In: Martin Beblo (Ed.): Environmental geophysics. Ernst & Sohn Verlag f. Architecture and technical sciences, Berlin 1997, ISBN 3-433-01541-4 .

[telford-1] William M. Telford, Lloyd P. Geldart, Robert E. Sheriff: Applied Geophysics. 2nd edition. Cambridge University Press, Cambridge et al. 1990, ISBN 0-521-33938-3 .

[shearer-2] A ^b Peter M. Shearer: Introduction to Seismology. Cambridge University Press, Cambridge et al. 1999, ISBN 0-521-66953-7 .

[lay-3] Thorne Lay, Terry C. Wallace: Modern Global Seismology (= International Geophysics Series. Vol. 58). Academic Press, New York NY et al. 1995, ISBN 0-12-732870-X .

[4] Peter Bormann (Ed.): New Manual of Seismological Observatory Practice (NMSOP). GeoForschungsZentrum, Potsdam 2002, ISBN 3-9808780-0-7 .

[5] Reinhard Kirsch, Wolfgang Rabbel : Seismic methods in environmental geophysics. In: Martin Beblo (Ed.): Environmental geophysics. Ernst & Sohn Verlag f. Architecture and technical sciences, Berlin 1997, ISBN 3-433-01541-4 .