Earthquake prediction
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An earthquake prediction is a prediction that an earthquake of a specific magnitude will occur at a specific location and time. Seismologists are not currently able to predict earthquakes with such accuracy, instead they focus on calculating the seismic hazards of a region and the probabilities that a given earthquake will occur.
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Controversy in trying to predict earthquakes
Earthquakes were once thought to be random geologic events without cycles or patterns. In some ways, earthquakes behave similar to the stock market, or types of events in nature that have properties described by chaos theory.
Like stocks, the pattern of earthquakes is quite capable of being correlated with anything, sometimes based on only one observation. Most empirical sciences, particularly the medical sciences, prefer to have hundreds, thousands, or even millions of data points before drawing conclusions regarding such things as the link between cigarettes and cancer, or fatty-foods and heart disease.
With regard to predictive seismology, humans have tried to associate an impending earthquake with such things as animal behavior, electromagnetic fields, weather conditions, unusual clouds, radon gas in ground water, water level in wells and so on - thereby suggesting that the dataset of observed seismicity is dependent on a large number of external variables.
Controversy arises as a result, since conclusions usually should not be made from a small data set unless a well understood physical phenomenon is present, particuarly when the data set is noisy or there are questions regarding how it is gathered.
Parkfield, California
Some types of earthquake predictions do not have to be ultra precise in magnitude, time and place to be socially useful. Predictions of a general nature can be quite useful if they are based on scientific principles.
For example, the region near the town of Parkfield in California has experienced a magnitude 6 earthquake approximately every 22 years since 1857. This led researchers to predict that a similar quake would hit the region between 1988 and 1992. As a result of this prediction, the area around Parkfield was heavily instrumented with monitoring equipment in order to record this event and researchers hoped any data collected would help in unlocking the secret of predicting future earthquakes.
However, the predicted earthquake failed to materialize on the expected fault, though a sizable quake did occur in nearby Coalinga, California in 1983. Some researchers believe the Coalinga quake may have released some of the stress on San Andreas Fault near Parkfield, and was a substitute for the missing quake.
If that was the case, then one would have expected that the next quake in the Parkfield region would be sometime in the mid 2000s. Another earthquake did in fact occur near Parkfield, this time in San Simeon, California in December 2003, but like the Coalinga earthquake in 1983, this quake was also not located on the San Andreas Fault. Regrettably, two fatalities were recorded in the town of Paso Robles as a result of strucure failure during the shaking.
On September 28, 2004, the expected Parkfield earthquake finally occurred. However, data returned has not yielded as much information as researchers had hoped.
Earthquake Prediction in China
Chinese earthquake prediction research largely based on unusual events before earthquakes, such as change of ground water levels, strange animal behavior and foreshocks. They successfully predicted the February 4, 1975 M7.3 Haicheng Earthquake[1] (http://www.eserc.stonybrook.edu/wise/HSfall2001/QuakePrediction.html), and the China State Seismological Bureau ordered an evacuation of 1 million people the day before the earthquake, but failed to predict the July 28, 1976 M7.8 Tangshan earthquake[2] (http://www.drgeorgepc.com/EarthquakePredictionChina.html). This failure put Chinese earthquake prediction research in doubt for several years. Chinese researchs now merged with western researchs, but traditional techniques are still common. Another successful prediction of the November 29, 1999, M5.4 Gushan-Pianling Earthquake in Haicheng city and Xiuyan city, Liaoning Province ,China was made a week before the earthquake. No fatalities, no injury. (People's Daily,[3] (http://web.peopledaily.com.cn/rmrb/199912/06/newfiles/col_19991206001042_jryw.html))
Other predictions
In early 2004, a group of scientists at the University of California, Los Angeles, lead by Dr. Vladimir Keilis-Borok, predicted that a quake similar in strength to the San Simeon earthquake would occur in a 12,000 square mile (31,100 km) area of Southern California by September of that year.
In April 2004, the California State Office of Emergency Services formally endorsed the prediction made by Kellis-Borik that there would be a strong earthquake in the Southern California region. The expected earthquake never occurred.
Based on the the historic record of the various published efforts to predict a quake, it might be easy to conclude that earthquake prediction is usually an imprecise, but nonetheless scientifically and socially useful art.
External links
- The USGS view on earthquake prediction http://www.geophys.washington.edu/SEIS/PNSN/INFO_GENERAL/eq_prediction.html
- Studies on Tide-Forming Forces and Earthquakes were published in 1967 (http://www.opteryx.de/docs/tamrazyan/Tamrazyan_1967.pdf) and 1968 (http://www.opteryx.de/docs/tamrazyan/Tamrazyan_1968.pdf) by Elsevier, but the U.S. Geological Survey: Common Myths About Earthquakes (http://earthquake.usgs.gov/faq/myths.html#5) contradicts this study.