"Highly unlikely, but not outside the realm of extreme possibilities."
Mulder, F.W. in the "The Jersey Devil" (1993)
The earliest documented case of unusual animal behaviour prior to an earthquake is recorded by the Roman historian Aelian in 373 B.C.; five days before an earthquake destroyed the city of Helike (once located at the coast of the Corinthian Gulf) various animals, like rats, weasels, snakes, centipedes and bugs supposedly emerged from the underground and fled from the city. In the following centuries many other cultures associated earthquakes with animals.
According to Japanese myth the cause of earthquakes is the giant catfish Namazu who lives buried in the underground. By moving his tail he can shake the entire earth and unfortunately he loves to cause trouble and havoc. However in early traditions the catfish also acts as premonition of danger, warning people from an imminent catastrophe or by swallowing dangerous water-dragons prevents further catastrophes.
Before the earthquakes of Edo (modern Tokyo) in 1855 and later in 1923 apparently catfishes acted weird, displaying increased activity and swimming to the surface of ponds and rivers.
Similar to Japan, also in China animals were regarded to possess some insights to the natural elements and disasters. Chinese authorities considered 58 species of animals to be useful for earthquake prediction, especially snakes, rodents and bats, and distributed booklets with depictions and descriptions of unusual animal behaviour worth to be reported.
In February 1975 hibernating snakes abandoned their hideouts in the north-eastern city of Haicheng. The city was evacuated and February 4, the region was hit by a 7.3 magnitude earthquake. More than 1.000 people were killed, but considering the densely populated area the prediction an evacuation was considered a great success.
Fig.1. & 2. Snakes and fishes are common animals in reports dealing with unusual animal behaviour prior to an earthquake. Both organisms possess particular sense organs: snakes can perceive vibrations and infrared radiation, fishes perceive electric fields. Maybe these senses help them to detect environmental changes, like weak foreshocks or variations in the local electromagnetic field, before a strong earthquake.
However just one year later on July 27, 1976 an unforeseen earthquake hit the city of Tangshan, killing 655.000 people. A later inquiry established that there were some reports on unusual animal behaviour; however the reports were ignored due the political tumults during the culture revolution. Before the Wenchuan earthquake (7.8 magnitude, 12.05.2008) apparently a migration of frogs was recorded in the city of Mianyang, located in the later area of devastation.
Also in the western civilizations stories about animals acting weird hours or days before an earthquake are repeatedly retold. One day before an earthquake devastated the Italian province of Friaul (6.5 magnitude, May 6, 1976) mice were seen running in open spaces and farm animals showed signs of restlessness.
After the earthquake and devastating tsunami of Christmas 2004 almost no carcasses of wild animals were found, apparently the animals fled into the interior of the islands before the arrival of the waves.
Also the earthquake in Virginia (5.8 magnitude, 23.08.2011) was sensed by the animals at the Smithsonian's National Zoological Park in Washington. Most animals reacted to the shakes by a general restlessness, but apparently apes climbed onto trees some minutes to seconds before the shakes were noted by the zoo staff.
The problem with this long (and far from exhaustive) list is that almost all these cases are anecdotes, reported after the earthquake and based on the subjective impression of what was considered at the time an unusual behaviour for an animal. Many anecdotes are also retold in the literature or in the web out of context. The evacuation of Haicheng was based mainly on a sequence of foreshocks that occurred months and days before the earthquake and the authorities had suspected for years that a larger earthquake could occur in a region with past strong earthquakes. The animals didn't behaviour strange without lacking an apparent reason (and "foresee" an unexpected earthquake), but reacted to the continued and almost daily trembles and foreshocks.
"The plural of anecdote is not data", however anecdotes can be used to formulate a hypothesis: are there environmental changes caused by tectonic tensions that could be detected by an organism?
It is almost sure that there exists no specific animal sense to detect an earthquake; Bora Zivkovic discusses the particular, however not paranormal, senses of animals on his "Observations". It seems however reasonable to assume that animals show reactions to variations of their environment caused by an earthquake or the tectonic processes that can cause an earthquake.
There are two kinds of unusual animal behaviour reported in the literature: Short time reactions, minutes or seconds before the earthquake, and long term reactions, days to weeks before the event.
Various physical phenomena were proposed to explain why animals react to incoming seismic waves some moments before humans do.
- Many animals can perceive infrasound that propagates much faster in the air (330m/s) than a Tsunami (200m/s). This could explain why animals apparently fled from the approaching Tsunami in 2004. Low-frequency sound waves and vibrations from weak foreshocks can be felt by animals like elephants or birds, fracturing rocks generate high frequency sounds that could be heard by rodents.
- An earthquake is composed of various types of seismic waves. P(rimary)-waves travel 1,7x faster than the more destructive S(econdary)-waves. Similar to infrasound waves and tsunami waves, this relative difference in velocity could explain the apparent reactions of animals some moments before the stronger S-waves arrive.
Explaining long term reactions is much more difficult.
-Fishes, birds and other animals can detect changes in the electric or magnetic field and accumulating tensions building up in the crust could also affect the local fields, however in case of magnetic variations this effect is very weak.
- Snakes and some insects can detect thermal variations based on their infrared vision. The physicist Friedemann T. Freund demonstrated in 1993 that rocks under tension emit infrared radiation and infrared anomalies were also recorded by the NASA Terra satellite before the magnitude 7.9 Bhuj earthquake (India) January 21, 2001. Maybe snakes can "see" the accumulating stress applied to rocks by telluric movements.
- Based on these observations in the last years also an "Electrical Field Hypothesis" was proposed. In a first version of this idea the accumulating tectonic tensions cause a current of electric charges in the rocks due the piezoelectric effects of minerals like Quartz. However as noted by Andrew Alden on a discussion on "Earthquake Lights" (caused supposedly by such electric fields) the generated voltage is negligible.
The "p-Hole Theory", also formulated by Freund, assumes that negative charged oxygen ions are removed from the respective position in the structure of a mineral, a positive charged "hole" remains in the crystal. These holes migrate to the surface of the mineral grain and can ionize other atoms, which are released into the atmosphere or the groundwater. GRANT et al. 2011 use this mechanism to explain the supposed disappearance of mating toads some days before the earthquake in L'Aquila on April 6, 2009 (the news based on GRANT et al 2010 about "earthquake predicting frogs" became very popular in the media). The paper proposes that charged ions modified the water chemistry of the aquifer and springs of the area and that the toads reacted to these variations in their usual environment. After the earthquake and release of the tectonic tensions also the ionization effect of the rocks disappeared, bringing the water chemistry back to normal levels.
Fig.3. The observations of GRANT et al. in spring 2009 (click on figure to enlarge) at the reservoir of San Ruffino (some km distant from the later epicentre of the earthquake of L'Aquila April 6, 2009). The research focused on the mating behaviour of toads (Bufo bufo). Some days before and after the earthquake the number of observed male toads decreased apparently without a specific reason.
The upper line shows disturbances in radio signals, caused by interferences in the ionosphere. According to the proposed scenario the accumulation of positive charges on the ground due tectonic tensions influenced the ionosphere and therefore can be used as a proxy of the release of ions into the environment of the toads. In the end the toads reacted to chemical changes caused by these ions.
It is important to note that these are all plausible, but hypothetical mechanisms. It is almost impossible to test the behaviour of an organism for a not foreseeable event like an earthquake. Animals in the wild or the zoo could react to other environmental factors, when coincidentally an earthquake occurs. The rare observations of animals in a laboratory during an earthquake show contradictory results, sometimes behaviour interpreted as unusual was observed, in other cases nothing happened or the supposed reactions were exact the opposite than recorded by other researchers.
We can assume that some animals are influenced by environmental changes that can occur before an earthquake; however our understanding of such possible precursor effects and how organisms react to them is still limited. As long as this gap exists the unusual behavior of animals alone can not be used to evaluate an increased earthquake risk.
BHARGAVA, N.; KATIYAR, V.K.; SHARMA, M.L. & PRADHAN, P. (2009): Earthquake Prediction through Animal Behavior: A Review. Indian Journal of Biomechanics: Special Issue NCBM 7-8: 159-165
GRANT, R.A. & HALLIDAY, T. (2010): Predicting the unpredictable; evidence of pre-seismic anticipatory behaviour in the common toad. Journal of Zoology 281(4): 1-9
GRANT, R.A.; HALLIDAY, T; BALDERER, W.P.; LEUENBERGER, F.; NEWCOMER, M.; CYR, G. & FREUND, F.T. (2011): Ground Water Chemistry Changes before Major Earthquakes and Possible Effects on Animals. Environmental Research and Public Health 8: 1936-1959
IKEYA, M. (2004): Earthquakes and Animals: From Folk Legends to Science. World Scientific, London: 295
KIRSCHVINK, J.L. (2000): Earthquake Prediction by Animals: Evolution and Sensory Perception. Bull. Seism. Soc. Am. 90(2): 312-323
SCHNYTZER, Y. (2011): Animal Modeling of Earthquakes and Prediction Market. Working paper
TONG, K. (1988): Abnormal Animal Behavior and the Prediction of Earthquakes. Master Thesis Dep. Earth Sciences Northeastern Illinois University.