The belief that animals can sense disasters, especially earthquakes, has been around for centuries. There are many accounts of unusual phenomena prior to an earthquake, especially anomalous animal behaviour. One of the earliest was by the Roman writer Claudius Aelianus about the destruction of Helike, a Greek city, by earthquake and tsunami in 373 BC:
For five days before Helike disappeared, all the mice and martens and snakes and centipedes and beetles and every other creature of that kind in the city left in a body by road that leads to Keryneia. ... But after these creatures had departed, an earthquake occurred in the night; the city subsided; an immense wave flooded and Helike disappeared....
Accounts of similar anticipation have been noticed throughout history. Catfish moving violently, bees leaving their hives in panic and chickens that stop laying eggs have been reported. Many pet owners, including me, witness dogs and cats behaving weirdly - howling or whining for no reason at night, restlessness, or showing signs of nervousness. For example, in Haicheng, China, in 1975, many people spotted snakes fleeing from their burrows a month before the city was hit by a strong earthquake. Now this is particularly very odd because it occurred during winter. During winter, the snakes were in between their annual hibernation; and the temperatures outside were nearly equal to suicide for the cold-blooded reptiles.
How do they sense earthquakes?
We have not properly understood how animals can predict or sense earthquakes yet, but scientists have never failed to try. The following are some plausible theories:
Chemical changes inside the earth
Scientists at the US space agency have studied the chemical changes that occur when rocks are under extreme stress. They think that these changes are linked to animal prediction. NASA geophysicist Friedemann Freund showed that, when rocks were under very high levels of stress, they release charged particles. These particles can flow out into surrounding rocks. When they arrive at the Earth's surface they react with air - converting air molecules into charged particles known as ions. These positive airborne ions are known to cause headaches and nausea in humans and to increase the level of serotonin, a stress hormone, in the blood of animals. They can also react with water and turn into hydrogen peroxide.
This can explain why frogs and toads leave their breeding colony before earthquakes since this chemical chain of events could affect the organic material dissolved in the pond water - turning harmless organic material into substances that are toxic to aquatic animals.
Changes in seismic waves
Vp is the symbol for the velocity of a seismic "P" (primary or pressure, as they call it) wave passing through rock, while Vs is the symbol for the velocity of the "S" (secondary or shear) wave. Laboratory experiments conducted by scientists have found that the ratio of these two velocities (Vp/Vs) changes when a rock is near to the point of fracturing.
The primary waves travel about twice as faster through the earth's crust than the secondary waves, so they arrive first. The greater the distance, the greater the delay between them. For an earthquake strong enough to be felt over hundred miles, this can amount to some tens of seconds difference. Primary waves are weaker, and often unnoticed by people.
This can explain why animals were alarmed and started behaving strangely a few seconds before the earthquake. However, this was not much of a prediction as a warning of shaking from an earthquake that has already happened.
How do we predict earthquakes?
Most rocks in the lithosphere contain a certain amount of gases which can be isotopically differentiated from normal atmospheric gases. There have been many reports of rise in concentration of such gases prior to a major earthquake; this has been stated to release due to pre-seismic stress or rock fracturing.
Radon is one of these gases, which is produced by radioactive decay of the trace amounts of uranium present in most rocks. Radon is attractive and known as a potential earthquake predictor because it is radioactive which can be easily detected, and its short half-life makes it sensitive to short-term fluctuations.
However, there is still much research to be done on this subject. Regardless of how animals sense these events, animal warning behavior has the potential to save hundreds of thousands of lives and warrants further research. China is the leader in early warning animal behaviour signs. However, shockingly, most government do not take this research seriously.
There is a growing number of researchers studying animal behaviour in relation to seismic events. Humans have, from the beginning, been very curious, and we have to stay this way. If we lose curiosity for the universe which we live in, we will not be able to discover anything new. So keep thinking, questioning and answering. :)
References & Resources
- Victoria, G. (2011). How animals predict earthquakes. BBC: Nature.
- Grant, R. A. and Halliday, T. (2010), Predicting the unpredictable; evidence of pre-seismic anticipatory behaviour in the common toad. Journal of Zoology, 281: 263–271.
- Mott, M. (2003). Can Animals Sense Earthquakes? National Geographic News.
- Earthquake prediction. Wikipedia.
- Animals & Earthquake Prediction. U.S. Geological Survey.
- Can Animals Predict Earthquakes? (2012). LiveScience.
- Kirschvink, J. L. (2000), Earthquake Prediction by Animals: Evolution and Sensory Perception. Bulletin of Seismological Society of America, 90, 2, pp. 312-323.
- Swanson, T. (2010), Earthquake prediction and Animals. University of Washington.
- VAN method. Wikipedia.
- All images (including featured image) via Wikimedia Commons.
To find out some typical animal behaviour, please see Smithsonian National Zoological Park's publication.