An 'earthquake prediction' is a
prediction that an
earthquake in a specific
magnitude range will occur in a specific region and time window. Predictions are considered as such to the extent that they are reliable for practical, as well as scientific, purposes. Although there is evidence that at least some earthquakes in some tectonic regimes are predictable with useful accuracy of time and space, the reliability and reproducibility of prediction techniques have not been established and are therefore generally not accepted by
seismologists. For practical purposes, seismologists bring forth
seismic hazard assessment programs by estimating the
probabilities that a given earthquake or suite of earthquakes will occur.
Controversy in trying to predict earthquakes
In the effort to predict earthquakes, people have tried to associate an impending earthquake with such varied phenomenon as seismicity patterns,
electromagnetic fields, weather conditions and
unusual clouds,
radon or
hydrogen gas content of soil or ground water, water level in wells,
animal behavior.
Thus far, earthquake prediction is controversial because data are sparse and there is little evidence or verified physical theory to link observable phenomena to subsequent seismicity. The frequent practice of polishing predictions after the fact further complicates matters. And, of course, given enough predictions, it is virtually inevitable that some will succeed "by chance." Assessing whether a successful prediction is a fluke is challenging. Most assessments rely on chance models for earthquake occurrence, models that are difficult to test or validate, because large earthquakes are so rare, and because earthquake activity is naturally clustered in space and time.
Predictions versus forecasts
A meaningful earthquake prediction must have all the following elements:
★ Specific area
★ Specific magnitude or magnitude range
★ Specific time window
★ Estimate of probability compared to random chance
★ A physical basis
A meaningful 'forecast' does not require the same accuracy, rather the term refers to prognostications on a longer time scale that are usually probabilistic.
Tidal forces
There are two flavors of tidal stressing that have been claimed to generate enhanced rates of earthquakes - diurnal and biweekly tides. The diurnal correlations would arise from more earthquakes only during the hours when the tidal stress is pushing in an encouraging direction, in contrast, biweekly effects would be based on earthquakes occurring during the days when the sinusoidal stressing oscillations are largest. The former, as most easily observed in the twice-daily rise and fall of the ocean tides, have occasionally been shown to influence tides (e.g.,
[1], this paper shows there may be some weak tidal triggering of shallow, oceanic thrust-faulting earthquakes). The latter, which arises from the periodic alignment of the Sun and Moon, has often been claimed in the popular press to incubate earthquakes (sometimes termed the "syzygy" effect) and occasionally for small datasets in the scientific literature (e.g.,
[2]), but generally such effects do not appear in careful studies of large datasets.
Syzygy, which is not given much credence in the scientific community, is motivated by the observation that, historically, there have been some great earthquakes whose timing with when the tidal forces are near their maximum. For maximum tidal force, three factors must coincide: First, when the moon (in its elliptical orbit) is closest to the earth; second, when it is within a day or two of a new moon (so that the tidal forces of the moon and sun are acting in concert); and third, when the earth (in its elliptical orbit) is at or near its closest distance to the sun.
Shallow earthquakes near mid-ocean ridges, volcanic earthquakes, and episodic tremor and slip have also been observed to sometimes correlate with the diurnal tides, with enhanced activity correlating with times that faults are unclamped.
Earthquake prediction in China
Chinese earthquake prediction research is 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
[3] Course notes for a workshop held at the Mineral Physics Institute at the Stony Brook University. 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.
[4] This failure put Chinese earthquake prediction research in doubt for several years.
Chinese research has now merged with Western research, 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 or injuries were reported.
[5]
Demeter microsatellite
The
CNES satellite has made observations which show strong correlations between certain types of low frequency electromagnetic activity and the seismically most active zones on the Earth, and have shown a sharp signal in the
ionospheric electron density and
temperature near southern Japan seven days before a 7.1 magnitude occurred there (on
August 29 and
September 5,
2004, respectively).
[6]
Animal behavior
It is claimed that animals can detect the
P-wave or
ultrasonic wave generated by a big underground explosion or the rupture of an earthquake, even if the waves are too small for humans' senses. These waves travel faster than the Love and Rayleigh earthquake waves that most strongly shake the ground and causes the most damage; when this happens, animals can detect the incoming earthquake wave, and start behaving agitatedly or nervously.
Others postulate that the animal behavior is simply their response to an increase in low-frequency
electromagnetic signals. The
University of Colorado has demonstrated that electromagnetic activity can be generated by the fracturing of crystalline rock. Such activity occurs in fault lines before earthquakes. According to recent research, electromagnetic sensors yield statistically valid results in predicting earthquakes — modern science's answer to centuries of human observation of animals.
[7]
Some people believe that in these ways, animals sense the immediate onset of earthquakes. In support of this claim, instances are cited when people have witnessed flight of animals just before an earthquake disaster. In fact, according to the Chief conservator of forests for the
Indian state of
Tamil Nadu, a few minutes before the killer
tsunami waves generated by an underwater earthquake hit the Indian coastline in December 2004, a 500-strong herd of blackbucks rushed away from the coastal areas to the safety of a nearby hilltop. Since the beginning of recorded history, observations of unusual animal behavior before earthquakes have been recorded by people from almost all civilizations. The Chinese began a systematic study of this unusual animal behavior and in December 1974 predicted a major earthquake that did, in fact, occur in February 1975. But skeptics claim to debunk nearly all such observations. In fact, the 1975 prediction relied most heavily on a series of strong foreshocks. The animal behavior reports are often ambiguous and not consistently observed. There is little evidence for animals being able to sense impending earthquakes, although it is likely they can sense the initial, weaker P-waves before people. Seismometers remain much more sensitive than even the animals, however.
In folklore, some animals have had more reports of being able to predict earthquakes than others, especially dogs, cats, chickens, horses, and other smaller animals. There have been reports with elephants, as well. Goats, cows, and most larger animals are generally reported as being less able to predict earthquakes.
Japan has a long tradition associating catfish with earthquake prediction. From this idea emerged a long university research programme concluding in 2004 in which it was proposed that the (established) high sensitivity of catfish to electric fields was involved in detecting fields of a few hertz because of piezoelectric effects on deeply buried quartz crystals. Actual monitoring of catfish and correlation with earthquakes gave results that are not promising.
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. The odds were given as 50/50.
In April 2004, the
California Earthquake Predicition Evaluation Council (CEPEC) evaluated Keilis-Borok's prediction and reported to the
California State Office of Emergency Services.
[8] CEPEC concluded that the "uncertainty along with the large geographic area included in the prediction (about 12,400 square miles) leads (us) to conclude that the results do not at this time warrant any special policy actions in California.” The predicted time window came and went with no significant earthquake.
Based on the historic record of the various published efforts to predict a quake, one might conclude that earthquake prediction is usually imprecise, but remains an art that is scientifically and socially useful.
According to new research to be published by Prof. Shlomo Havlin, of Bar-Ilan University's Department of Physics, earthquakes form patterns which can improve the ability to predict the timing of their recurrence. In November 2005 (November 11 issue) the journal ''
Physical Review Letters'', published by the
American Physical Society, published an article by researchers from Israel and Germany that say that there is a way to predict when the next earthquake will hit.
Prof. Shlomi Havlin's from
Bar-Ilan University in Israel, in collaboration with Prof. Armin Bunde, of the
Justus-Liebig University in Giessen, Germany, and Bar-Ilan University graduate student Valerie Livina used the "scaling" approach from physics to develop a mathematical function to characterize earthquakes of a wide range of magnitudes in order to learn from smaller magnitude earthquakes about larger magnitude earthquakes. The team's findings reveal that the recurrence of earthquakes is strongly dependent on the recurrence times of previous earthquakes.
This memory effect not only provides a clue to understanding the observed clustering of earthquakes, but also suggests that delays in earthquake occurrences, as seen today in Tokyo and in San Francisco, are a natural phenomenon.
In another paper in the journal ''
Nature'', Richard Allen of the University of California claims that the distinction between small and large earthquakes can be made from the very first seconds of seismic energy recorded by seismometers, though other scientists are not convinced.
[9] If correct this may make earthquake early warning (as distinct from prediction) more powerful. Earthquake early warning provides an alarm that strong shaking is due soon to arrive, and the more quickly that the magnitude of an earthquake can be estimated, the more useful is the early warning. However, earthquake early warning can still be effective without the ability to infer the magnitude of an earthquake in its initial second or two.
Loma Prieta, California
From 1968 to 1988 scientists in California mapped seismic activity on a cross section of the fault lines. They identified a "seismic gap" in the Loma Prieta area from various features of the regional seismicity. They therefore concluded that Loma Prieta was due for an earthquake. On
17 October 1989 the
Loma Prieta earthquake occurred, initially reported as measuring 7.1 on the Richter scale but later more accurately recorded as moment magnitude 6.9, causing 63 deaths. This prediction, however was not very useful as it could not predict the exact date.
See also
★
Forecasting
★
Earthquake storm
★
Earthquake weather
★
Earthquake warning system
★
Jim Berkland (and the role of the
moon)
References
1. Earth tides can trigger shallow thrust fault earthquakes, E. S. Cochran and J. E. Vidale and S. Tanaka, , , Science,
2. Tidal correlations of seismicity, John H. Glaser, , , Geology: Online Forum - Breathing of the seafloor,
3. Earthquake Prediction: Haicheng, China - 1975 Glenn Richard
4. Earthquake Prediction in China George Pararas Carayannis
5. 海城岫岩地震预测准确 (In Chinese.)
6. Satellite défilant du CNES (France) (In French.)
7. Earthquake [earthquake warning systems], T. Bleier and F. Freund, , , Spectrum, IEEE,
8. Report to the Director, Governor's Office of Emergency Services California Earthquake Prediction Evaluation Council
9. The start of something big?, Rachel Abercrombie, , , Nature,
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 and
1968 by
Elsevier, but the
U.S. Geological Survey: Common Myths About Earthquakes contradicts this study.
★
PetQuake - Encourages users to submit reports of atypical animal behavior and produces real-time dot map of the United States
★
When Will the Next Earthquake Occur?
★
Stopping the next big one - Is Earthquake prediction and prevention possible?
★
Earthquake Predictions
★
The Earthquake Weather Project
★
Earthquake Prediction - updated daily
Earthquake prediction by geometric relationship of planets, moon, and sun.
★
Astronomical/astrological geometric relationship prediction
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