Microseism

This product was added because of Geosciences content, defects on the quality assurance side of the portal. This is done to increase the quality of articles in the topic area of Earth Sciences. Please help to rectify the defects, or take part in this discussion. ( )

The oscillations of the earth (including natural frequencies of the earth or Erdbrummen ) consist of a superposition of dozens of low-frequency oscillations, which occur continuously in the Earth's body, that is, independent of events such as earthquakes or volcanic eruptions. However, there are seasonal influences.

A similar effect is also seen in other planets suspected ( eg, Mars), then one speaks generally of planetary hum. Demonstrated such self-oscillations are also for the sun.

• 3.1 General
• 3.2 Seasonal effects

• 4.1 Objectives
• 4.2 prehistory
• 4.3 History and Methods

Term

Internationally, the English term is hum (English for " hum " ) is used. However, this is ambiguous. Among low-frequency humming noise on the one hand, these having locally dependent and are also not heard of any (humming phenomenon). Also the already longer known micro-earthquakes (English microseisms ), which are caused by atmosphere and oceans are called in English or hum hum Earth.

Properties

General

Approximately 60 different frequencies are superimposed in the range 3-7 millihertz and form an inaudible from people with hearing mixture in the infrasonic range. The vibration are so weak, so that they can be registered only with highly sensitive measuring devices.

An important feature of this frequency mix is that it is not a harmonic series (similar as a bell that is struck ), but rather a mixture of different frequencies (similar to an orchestra ).

Species

There are two types of vibrations, spheroidal and toroidal. Both modes of vibration each carry about half of the total effect.

Spheroidal oscillations

The spheroidal oscillations take place vertically. At the same time results in a slight forward and backward movement, making a total of an elliptical movement is generated. It is per minute. The rashes range from a few tenths of a micrometer.

Toroidal oscillations

This exercise is carried horizontally, but twisted in a complicated way. Toroidal oscillations also occur by the minute.

Causes

General

While it is believed today to understand spheroidal vibrations good to give the toroidal oscillations still a mystery.

The cause of the spheroidal oscillations previously pressure fluctuations, as they cause the movements of ocean and atmosphere are.

Cause of the toroidal oscillations are shear forces, their origin, however, so far is unclear. There are numerous assumptions, all of which so far are, however, speculative and at best explain small parts of the toroidal oscillations:

• Topographic effects of deep-sea mountains were adopted, they should divert pressure in shear forces mountains on the sea floor.
• Likewise, should transfer kinetic energy between the two modes of vibration an invisible coupling. This coupling is based on the shape of the earth, which is not exactly spherical but slightly flattened at the poles.
• Earthquakes are to encourage the toroidal oscillations.
• Even the large-scale rotation of air around low-pressure areas has been blamed.

The difficulty to explain the toroidal oscillations is to measure it in the difficulty. Local air pressure fluctuations are superimposed on the toroidal oscillations of the earth. To measure them, so underground observatories are necessary, which isolate the measuring instruments against such fluctuations.

Seasonal effects

The spheroidal oscillations are subject to seasonal effects. The strongest are those when each winter prevails on the northern or southern hemisphere.

• From December to February are the strongest vibrations from the northwest,
• June-August from the south.

A possible explanation for this is provided by a theory that was put forward by Junkee Rhie and Barbara Romanowicz of the University of California at Berkeley, 2004. After storms came as the cause in question. Strong storms rage in winter over the seas and create waves that reach down to the bottom and this " knead ". Is on the Northern Hemisphere winter, these storms rage, especially in the North Atlantic and the North Pacific. In winter in the southern hemisphere they romp around mainly in the seas around Antarctica.

However, the toroidal oscillations can thus not be explained by this effect.

Research

Objectives

In addition to the declaration of the toroidal oscillations be expected from the study of Erdbrummens especially a better understanding of the interaction of the atmosphere, solid earth body and seas, and from this, in turn, improved climate models. In addition, it is hoped that new insights into the internal structure of the Earth but also other planets, such as Mars.

Prehistory

Already in Ancient Greece existed the idea of ​​a " harmony of the spheres ". The movements of the planets should, inaudible to humans, produce planetary tones. Even in 1619 postulated the astronomer Johannes Kepler in his Harmonice Mundi such a harmony of the spheres. Although now outdated scientifically, the idea of ​​the harmony of the spheres is still interest in art and esotericism.

The Chinese astronomer Zhang Heng invented 132 AD, the first known seismoscope. Even in the former unit came a pendulum for use.

Ernst Florens Friedrich Chladni in 1794 founded the modern acoustics. He showed that acoustic oscillations are to be considered material in relation independent of the air. This simultaneously laid the foundation for the modern seismology because seismic waves ultimately are nothing more than the vibration of the materials that make up the earth.

Luigi Palmieri invented around 1856 electrical seismograph.

Emil Wiechert in 1897 developed the first seismograph, which was suitable for studies of the earth's crust. In 1898 he became a professor at the University of Göttingen. That same year, his institute was transformed into the world's first Institute of Geophysics. From 1899 he led in the observatory measurements with pendulums and light pointers by, from 1902 in the newly established seismological Göttingen, the oldest still in operation seismological station in the world. He wrote books and made ​​important discoveries. Wiechert thus became the founder of modern seismology.

1960 discovered the American physicist Robert B. Leighton, the natural oscillations of the sun, thus paving the helioseismology.

Traditionally, the focus of seismology was always on the registration of earth and tsunami, volcanic eruptions, as well as artificially induced vibrations (see seismology), not least because such events far stronger vibrations cause than the Erdbrummen. Over time, however, always more sensitive instruments have been developed pendulum seismometers and gravimeters, but also powerful computers, which eventually created the technical conditions for the discovery and exploration of Erdbrummens.

History and Methods

1998 spheroidal vibrations of Kazunari Nawa and Naoki Suda were from the University of Nagoya detected by the mathematical analysis of the seismic data, which had been collected for the first time for several years.

The study of toroidal oscillations, however, prepared a long time problems. Cause is, strangely enough, the fact that these are stronger than the spheroidal oscillations. However, this is due to local influences, such as changes in air pressure. To exclude such local influences, underground observatories are used, such as the Black Forest Observatory ( BFO ) near Schiltach in Baden- Württemberg. The discovery of toroidal oscillations finally succeeded Dieter Kurrle and Rudolf Widmer- Schnidrig at BFO, after they had compared the local measurements with those from China and Japan.

Therefore, the study of toroidal oscillations is also incredibly difficult because only a few observatories can provide appropriate data. Is there world over a hundred observatories that provide data for the vertical vibrations, so it is in the toroidal four straight times.

The following is a table of the stations and data channels, the data were used for the study of the toroidal swing.

Progress is hoped that in the future through simulations using supercomputers.

Also space missions are planned for the future. The ESA ExoMars program provides to land until 2019 at the latest on Mars to perform, inter alia, seismic measurements there. The same had already been planned in the late 1990s. In CNES -led project Netlander should be exposed at four different sites of the Mars landing capsules for seismic measurements. In 2003, the project was stopped.

Music

• Kookoon: INNER EARTH. Seismosonic Symphony. In 1999. Traumton Records. CD 4492-2.