An earthquake prediction is a prediction that an earthquake of a specific magnitude will occur in a particular place at a particular time (or ranges thereof). Despite considerable research efforts by seismologists, scientifically reproducible predictions cannot yet be made to a specific day or month.

However, for well-understood faults seismic hazard assessment maps can estimate the probability that an earthquake of a given size will affect a given location over a certain number of years. The overall ability to predict earthquakes either on an individual basis or on a statistical basis remains remote.

Once an earthquake has already begun, early warning devices can provide a few seconds’ warning before major shaking arrives at a given location. This technology takes advantage of the different speeds of propagation of the various types of vibrations produced. Aftershocks are also likely after a major quake, and are commonly planned for in earthquake disaster response protocols.

Experts do advise general earthquake preparedness, especially in areas known to experience frequent or large quakes, to prevent injury, death, and property damage if a quake occurs with or without warning.

Prediction techniques

In the effort to predict earthquakes people have tried to associate an impending earthquake with such varied phenomena as seismicity patterns, electromagnetic fields (seismo-electromagnetics), ground movement, weather conditions and unusual clouds, radon or hydrogen gas content of soil or ground water, water level in wells, animal behavior, and the phases of the moon.

Many pseudoscientific theories and predictions are made, which scientific practitioners find problematic. The natural randomness of earthquakes and frequent activity in certain areas can be used to make “predictions” which may generate unwarranted credibility. These generally leave certain details unspecified, increasing the probability that the vague prediction criteria will be met, and ignore quakes that were not predicted. Rudolf Falb’s “lunisolar flood theory” is a typical example from the late 19th century.

Evaluation of prediction theories

Official earthquake prediction evaluation councils have been established in California (the California Earthquake Prediction Evaluation Council) and the federal government in the United States (the National Earthquake Prediction Evaluation Council), but have yet to endorse any method of predicting quakes as reliable.

Scientific evaluations of prediction claims look for the following elements in a claim:

• A specific location or area
• A specific span of time
• A specific magnitude range
• A specific probability of occurrence

Radon

Emission of radon as a quake precursor was studied in the 1970s and 80s with no reliable results and continued to be dismissed by most seismologists until recently. However, after the 2009 L’Aquila earthquake, which was preceded by an Italian laboratory technician’s predictions of an impending major earthquake, some in the scientific community expressed renewed interest in radon as a quake precursor. In December 2009, the technician, Giampaolo Giuliani, presented his research to the American Geophysical Union in San Francisco and was later invited by the American Geophysical Union to participate in developing a worldwide seismic early warning system.

The VAN method

VAN is a method of earthquake prediction proposed by Professors Varotsos, Alexopoulos and Nomicos in the 1980s; it was named after the researchers’ initials. The method is based on the detection of “seismic electric signals” (SES) via a telemetric network of conductive metal rods inserted in the ground. The method stems from theoretical predictions by P. Varotsos, a solid-state physicist at the National and Capodistrian University of Athens. It is continually refined as to the manner of identifying SES from within the abundant electric noise the VAN sensors are picking up. Researchers have claimed to be able to predict earthquakes of magnitude larger than 5, within 100 km of epicentral location, within 0.7 units of magnitude and in a 2-hour to 11-day time window.

Pattern theories

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. Shlomo 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 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.

Magnitude problem

In a 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. 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.

Animal early warning

Animal behavior reports are often ambiguous and not consistently observed. In folklore, some animals have been identified as being more able to predict earthquakes than others, especially dogs, cats, chickens, horses, toads and other smaller animals.

It has been postulated that the reported animal behavior before an earthquake 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 one study, electromagnetic sensors yield statistically valid results in predicting earthquakes.

In Italy, findings from 2009 suggest that toads are able to detect pre-seismic cues.

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 earthquakes (e.g., 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.,), but generally such effects do not appear in careful studies of large datasets.

Tidal forces are magnified during and after an eclipse. The solar tide is approximately a third of the lunar tide. When the sun and moon are in alignment these tidal forces are combined.

A paper published in Taiwan, by the Department of Astronomy, Beijing Normal University, found a significant relationship to tidal forces and earthquakes in China and Taiwan. The paper considers the relationship between 21 major earthquakes (Ms ≥ 7.0) in land and the offshore area of Taiwan island in the 20th century and the variance ratio of the lunar-solar tidal force. The result indicates that the time of these earthquakes is closely related to the variance ratio of the lunar-solar tidal force, and therefore that the tidal force possibly plays an important role in triggering earthquakes. The conclusion is this method may be used to help forecast earthquakes by studying the lunar perigee.

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 coincides with tidal forces 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.