Earthquake station
An earthquake observatory (also a seismological observatory ) is a place that is used to monitor both local and global seismicity . As a rule, these are buildings in a remote, protected location which, in addition to the office rooms used for evaluation, also have spatially separated parking spaces for the required measuring devices.
Site selection and instrumentation
These seismic waves are recorded with seismometers , which nowadays usually register the signal digitally on three components (vertical, north-south and east-west). In order to be able to gain as much information as possible from the seismograms , the recording is usually carried out in an extended frequency range. Some earthquake monitoring stations therefore have several different measuring instruments, the sensitivity of which lies in different frequency bands. In addition to earthquake activity , long-term phenomena such as B. the tidal range or the long-period natural vibrations of the solid earth can be recorded.
In order to be able to evaluate the data obtained as effectively as possible, various aspects must be considered when selecting locations for earthquake monitoring stations. The primary goal is to keep the useful signal as free as possible from background noise . Anthropogenic sources of noise are e.g. B. industrial plants, traffic routes with high volume of traffic or heavy goods traffic, intensively cultivated arable land and generally the use of heavy machinery. Earthquake control rooms are therefore primarily located in remote locations far from populated or economically used areas. Natural disruptive influences, such as the effects of wind, the sound of the sea or strong temperature fluctuations, must also be avoided. Modern measuring instruments are therefore often housed in disused or specially built shafts or tunnels and provided with thermal insulation .
Wind turbines in the vicinity represent a considerable disruptive factor for seismic stations. Scientists sometimes resist the relocation because measurement continuity is lost.
history
Even in the Chinese Empire there was a simple instrument that made it possible to identify the direction from which earthquake waves had come. This device by the Chinese Chang Heng from the year 132 had the shape of a vase and had dragon heads on the side that looked in different directions and each held a ball in its mouth. The jerky ground movement occurring during a tremor caused the ball of the dragon that was looking in the direction of the wave propagation to fall into the open mouth of a frog below due to its inertia and thus indicated the direction of the epicenter. Such earthquake indicators did not begin to be used in Europe until the early 18th century .
The first seismograph that could provide a true-to-time record of ground movement was built by an Italian named Cecchi and commissioned around 1875. However, its sensitivity was so weak that it was not possible to record an earthquake for the first time after twelve years. The first earthquake was therefore registered in Japan in 1880. However, the mechanical framework conditions continued to limit the sensitivity in such a way that recordings were only possible at a short distance from the epicenter of an earthquake. The first recording of a long-distance quake happened by chance in Potsdam by Ernst von Rebeur-Paschwitz , who actually carried out inclination measurements with a horizontal pendulum . In 1892 he succeeded in recording another long-distance quake in Strasbourg with an identical seismometer.
Thereafter, the technical development of seismometers increased rapidly and reached a mechanical standard in 1910, which, although further improved, only underwent a fundamental change again through the progress in semiconductor technology. In Germany, Emil Wiechert was primarily responsible for the improvement and development of seismometers. He had a seismometer built in Göttingen in 1902 and set up the Wiechert earthquake station, which is now named after him, in a tunnel . The instrument is considered to be the oldest seismograph still in operation. Devices of the same design were also put into operation in Leipzig, Potsdam, Strasbourg, Jena, Hamburg, Uppsala and Samoa by 1906.
Since then, the technology has continued to improve and many new earthquake control rooms have been set up. With advances in electrical and semiconductor technology , seismometers have become more handy and compact and can now be easily transported and installed in all parts of the world.
Over the decades, networks of seismometer stations have emerged that are maintained by various institutes in several countries, often in cooperation with local partners who carry out regular maintenance . Due to the advancing technical development, in particular of digital data transmission , the immediate proximity of the evaluating staff to the measuring instruments is increasingly required today. Modern stations usually offer the possibility of direct access to the Internet or data transmission via satellite connection, so that the number of real "earthquake stations" in the sense of staffed outstations is declining, while the station density continues to increase globally. The data are usually archived by connected data centers and held for evaluation.
purpose
Scientific benefit
The recording and investigation of the earthquake activity is primarily based on scientific interest and is therefore by no means limited to areas that are inhabited or are used economically. Seismic waves have a greater potential for exploring the inner structure of the earth than other investigation methods , as they collect information along their beam path . Due to the enormous release of energy during a strong earthquake, the earth's body is completely irradiated. Today's picture of the shell-shaped structure of the earth and the depths of the layer boundaries is mainly derived from seismological observations.
However, in many earthquake-prone countries there is an overlap with economic interests, since the investigation of local seismicity contributes to the understanding of the tectonic processes in the earth's interior and thus serves to improve the assessment of the regional hazard potential from earthquake activity. A basic task of earthquake services is the localization of earthquake sources . This is possible if an event has been registered at at least three different stations. The accuracy of the location depends, among other things, heavily on the number and the geometric arrangement of the earthquake monitoring stations. From the spatial distribution of the hypocenters , conclusions can be drawn about the location of active geological fault systems. From the waveform of an earthquake signal and its variation at different measuring locations, the focus mechanism can also be determined, which allows further insights into the geodynamic cause of the earthquake.
Defense against damage
Seismic stations that have a priority set for the purpose of a rapid warning of an imminent loss event, are on a continuous monitoring ( Monitoring dependent) of the earthquake activity. Earthquake stations, on the other hand, which are only used for research, also continuously record data, this may be stored locally for cost reasons and only accessed and evaluated with a time delay.
Seismological monitoring can serve to avert danger in various ways. In Japan , a country that is particularly at risk from severe earthquakes, earthquake monitoring stations are used to limit the damage directly: During an earthquake, different types of waves are emitted, which propagate at different speeds. The destructive surface waves are comparatively slow, so that after the first wave to arrive ( P wave ) has been registered, there is a small window of time in which important emergency measures can be taken. The duration of this warning time is only a few seconds (e.g. 20 s for a stove 60 km away), which can be used to interrupt electricity and gas lines. This minimizes the risk of major fires as a direct consequence of the quake. Train traffic can also be stopped to prevent derailments at high speed, for example.
However, earthquake stations can also provide early warning of other catastrophic events. Earthquake monitoring stations, for example, are of great importance in the early warning of the tsunami , as these tidal waves are usually preceded by a very strong undersea earthquake. Tsunamis can spread over extremely long distances and flood distant coastal areas. However, the tidal wave propagates much more slowly than earthquake waves, so that depending on the distance between the endangered coastal area and the epicenter of the tsunami-inducing earthquake, warning times of a few minutes to significantly more than an hour result. This time can be used for evacuation measures if appropriate emergency plans are activated .
A large number of seismological observatories were built in close proximity to active volcanoes in order to specifically observe the seismic activity below the volcanic cone. One of the oldest of these volcano observatories is the Hawaiian Volcano Observatory on the crater rim of Kilauea . Volcanic earthquakes are mostly triggered by the rise of magma and are shown in the seismogram by special manifestations, such as B. to recognize the tremor . In addition to seismic activity, volcanic observatories also observe other phenomena (including local uplifts, ground inclination, gas emissions, temperature) that could be signs of an impending eruption. With the help of such observatories, volcanic eruptions can already be predicted with some reliability.
Web links
Individual evidence
- ↑ Central Institute for Meteorology and Geodynamics ZAMG: Locations of all 321 IMS measuring stations
- ↑ Federal Institute for Geosciences and Natural Resources BGR: International Monitoring System (IMS)
- ↑ http://www.infranken.de/regional/forchheim/In-Haidhof-hoert-man-den-Pulsschlag-der-Welt;art216,472504
- ↑ http://smc.kisti.re.kr/quake/seismograph/index.html (Engl.)
- ↑ a b c Technical and historical aspects of seismographs by E. Wielandt; s. History section ( Memento of the original from March 18, 2011 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Wiechertsche Erdbebenwarte zu Göttingen, description of the building ( Memento of the original from May 2, 2005 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , accessed June 11, 2009
- ↑ erdbebenwarte.de - website of the Wiechert earthquake observatories in Göttingen
- ↑ Geophysics Uni Munich: Seismology - Earthquakes, pages 19–31
- ↑ Federal Institute for Geosciences and Natural Resources BGR: International Monitoring System (IMS)
- ^ "Seismology component" - GITEWS website
