Earthquake forecast
Earthquake prediction or earthquake prognosis is the totality of the methods, means and attempts to predict the occurrence of an earthquake of a certain magnitude at an exact time and in an exact location .
Because of the economic damage and possible victims ( mass panic or mass hysteria ), an early warning of the population of a single earthquake only makes sense if the number of expected earthquake victims is estimated to be very high, or if the earthquake is predicted very precisely in terms of space and time can be. The temporally and spatially precise, reliable prediction of earthquakes is not possible according to the current state of science. However, there are detection systems that offer an advance warning of a few seconds from the start of an earthquake, but this is no longer an earthquake forecast.
Probability of earthquakes
Basically, the triggering processes and the probability of an earthquake occurring in a certain area are scientifically understood. This applies above all to the general probability of occurrence of earthquakes, since the vast majority of them are bound to plate-tectonically active areas. Knowledge of the tectonic relationships therefore allows earthquake maps to be compiled for many areas of the world, which show the probability of earthquakes for this area on the basis of the statistical analysis of already registered earthquakes. A more accurate earthquake forecast is possible in well-known and intensively studied areas. Here, too, the uncertainty of the forecast is in the range of several months or years. When looking at individual events, a complicated interplay of a large number of influencing variables can be observed, so that the isolated consideration of a single variable is not promising for a successful prediction.
Precursor phenomena
A number of effects are known which can often be observed in the run-up to earthquake events and are referred to as precursor phenomena. Some of these express themselves in the change in geophysically measurable quantities, such as B. the seismic speed , the slope of the ground or the electromagnetic properties of the rock. Other phenomena are based on statistical observations, such as the concept of seismic calm , where in a potentially endangered region the background seismic activity , i.e. the steady occurrence of smaller earthquakes, decreases over a longer period and points to an impending major event. A statistical method is also based on a method that uses sudden changes in the probability density of the vertical component of seismic records.
The radon method measures the quantities in which the noble gas radon escapes from the earth. This method allows the most reliable forecasts to date. The indicator is the easy to check fact that before the earthquake the amount of radon in the water of shafts increases by up to four times the usual amount. According to seismologists, deep underground rock layers suddenly become permeable and cracked shortly before an earthquake, they expand, thereby releasing radon, penetrating the soil and concentrating close to the earth's surface. The best-known example of such measurements are the boreholes along the San Andreas Fault (also known as the San Andreas Trench), which are examined weekly for their extent in order to keep an eye on seismic changes.
Unusual behavior in animals shortly before major earthquakes and tsunamis has also been repeatedly reported. These reports are not statistically significant and can only rarely be used to forecast earthquakes.
Both measurable and statistically recorded precursor phenomena vary greatly in their time course (up to years) and in their order of magnitude. In many cases, one or more of these effects are completely absent. In addition, the instrumental effort that would be required for a complete recording of these phenomena would not be feasible, so that the possibility of an exact prediction of earthquakes for the near future is not to be expected.
Previous predictions
Occasional reports of successful predictions usually show little statistical significance given the frequency of earthquakes in the region concerned . So was z. For example, a Japanese scientist predicted an earthquake of magnitude 7 in Tokyo for the period from September 14th to 19th, 2003 due to an electromagnetic precursor phenomenon. An earthquake did indeed occur in Tokyo on September 20, 2003, but the magnitude was around 1.5 size classes lower, which corresponds to less than a hundredth of the predicted energy release. A much stronger earthquake (magnitude 8) with two strong aftershocks (Mag. 5.8 and 7) occurred a week later, on September 26th, but the epicenter was some distance away, about 80 km southeast of the coast of the main island Hokkaidō .
An example of a successful earthquake prediction is the Liaoning earthquake in Manchuria on February 4, 1975 in the People's Republic of China . Authorities ordered the evacuation of the metropolis of Haicheng the day before the quake, after observing an increase in smaller earthquakes that occurred at the end of a month-long period of changes in the elevation of the earth's surface and water table. In addition, strange animal behavior has been observed. It is estimated that without the evacuation the number of victims would have been around 150,000; however, it was 1300. However, z. For example, in the Tangshan earthquake on July 27, 1976 , which resulted in several hundred thousand deaths, according to various reports, no such clear signs that a brief advance warning was not possible. However, the statement about the absence of animal anomalies is incorrect. Immediately after the Tangshan earthquake, an extensive Chinese investigation committee, in which 16 scientific institutes participated, worked in the earthquake area. It provided 459 pages of documentation (in Chinese), which in Chapter 12 also commented in detail on abnormal animal behavior before the earthquake. It documents 2202 cases of conspicuous animal behavior that began one or two days before the quake and increased significantly towards the quake. Among them there was very unusual animal behavior that had never been observed before (around 100 weasels run into a village center, 300 mice motionless on the ground, a 100-meter-wide swarm of dragonflies, the bees from all 100 beehives in an apiary flee from these, several hundred snakes clenched together a pond edge). According to a participant in the commission of inquiry, the politicians responsible for the earthquake warning had been removed from their offices at the time of the earthquake. Because of this, the prediction based on nature observations may have failed.
See also
Web links
Individual evidence
- ^ A b Ruth Ludwin: Earthquake Prediction. US Geological Survey , September 16, 2004, accessed February 7, 2010 .
- ↑ Der Spiegel : Earthquake Forecast of a 14-Year-Old: The Fairy Tale of the Napa Valley of September 4, 2014, loaded on July 7, 2016
- ↑ Earthquake warning system in use. derStandard.at , March 9, 2009, accessed on April 6, 2009 (article about existing advance warning technology with a lead time of a few seconds).
- ↑ P. Manshour, S. Saberi, Muhammad Sahimi, J. Peinke, Amalio F. Pacheco, M. Reza Rahimi Tabar: Turbulent-Like Behavior of Seismic Time Series . February 25, 2009, arxiv : 0902.4331 .
- ↑ Gerhard Harms: A new early earthquake warning system - Oldenburg physicist publishes study in Physical Review Letters. Science Information Service, December 29, 2008, accessed April 6, 2009 .
- ^ A method for continuous measurement of radon in groundwater for earthquake prediction . In: Journal of Geophysical Research . tape 82 , B8, March 1977, p. 1353-1354 , bibcode : 1977JGR .... 82.1353N .
- ^ Chi-Yu King: Radon emanation on San Andreas Fault. Nature , February 9, 1978, accessed April 6, 2009 (abstract).
- ^ San Andreas Fault Observatory at Depth reveals new insights into the earthquake machine. EurekAlert, December 5, 2005, accessed April 6, 2009 .
- ^ Haicheng, China. (No longer available online.) USGS, Earthquake Center, archived from the original on September 9, 2009 ; Retrieved February 7, 2010 . 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.
- ↑ Wang Fang: Historic Earthquakes: The 1976 Tangshan Earthquake. (No longer available online.) US Geological Survey , archived from the original on May 16, 2010 ; Retrieved February 7, 2010 . 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.
- ↑ Mei Shirong, Hu Changhe, Zhu Chuanzhen, Ma Jin, Zhang Zhaocheng, Yang Maoyuan: The Tangshan Earthquake of 1976 . In: Seismological Press . Beijing, China 1982.
- ↑ Jiang Jinchang, Institute of Biophysics, Academia Sinica, personal communication from 1988
