The mystery is one of Sherlock Holmes proportions; in 373 B.C., animals – dogs, snakes and weasels alike – escaped the Greek city, Helice, in droves mere days before a devastating earthquake (Mott, 2003). Reports of similar incidents have surfaced since, raising the question: can animals sense or anticipate earthquakes?
The answer is complicated.
Earthquakes occur due to sudden slips on a fault, the boundary between tectonic plates. They are constantly moving, causing a build-up of stress at their boundaries. If it overcomes the force of friction between the plates, they will slip and release large amounts of energy (SCEDC, 2018). This sudden activity creates seismic waves, propagating away from the focus, the point of the original movement (SCEDC, 2018). However, only earthquake forecasts can be made, and they lack certainty, with timeframes spanning several decades and no indication of precisely if or when. (American Geosciences Institute, 2018).
Some animal precursors can, however be explained by the elastic waves produced. When an earthquake occurs, S- and P-waves, propagate outward (Figure 1). As only P-waves are able to travel through the mantle, they arrive to a point of detection slightly before the larger S-wave. Though they usually cannot be felt by humans, animals with keen senses can, thus explaining how almost 60% of all observed cases where animals evacuated fell within the final five minutes before an earthquake (Kirschvink, 2000; U.S. Geological Survey, 2018).
From an evolutionary perspective, a seismic-escape behaviour pattern could indeed have evolved. All animals instinctively respond in order to escape from predators and maintain their lives (Kirschvink, 2000). Individuals with a genetic predisposal to stronger instincts would survive to pass on their genes to their offspring, causing an increase in the concentration of such alleles in the population. The theory of directional evolution suggests that it is possible for a genetic system for seismic-escape to have evolved, as it increases the chance of survival and thus, evolutionary fitness (Kirschvink, 2000).
Statistical analysis of over 180 publications studying abnormal animal behaviours prior to earthquakes shows remarkably similar probabilities for both foreshocks and animal precursors. While this suggests a correlation, most reports are based on anecdotal observations, making it difficult to confirm whether or not these behaviours are predicative or anomalies. Confirmation bias is also noteworthy, as people may only remember strange behaviours subsequent to the event. Moreover, ambiguity to the criteria, such as what defines normal behaviour or an anomaly, only further complicates studies (Woith, et al., 2018).
Despite the fact that animals react to a wide variety of events – being hungry, mating, predators, major earthquakes have been successfully forecasted based on this phenomenon (Mott, 2003). For instance, in 1975, Chinese officials ordered the evacuation of Haicheng days before a 7.3-magnitude earthquake based in part on strange animal behaviour. It is estimated that the number of injuries could have exceeded 150,000 had it not occurred, giving people hope that quakes could indeed be predicted (Mott, 2003).
Still, until conclusive results can be attained, seismic animal precursors remain a mystery.
Works Cited
American Geosciences Institute, 2018. Can Earthquakes be Predicted? [online] American Geosciences Institute. Available at: <https://www.americangeosciences.org/critical-issues/faq/can-earthquakes-be-predicted> [Accessed 19 Oct 2018].
Earle, S., 2015. Physical Geology. Creative Commons Attribution 4.0 International License, 2015.
Kirschvink, J.L., 2000. Earthquake Prediction by Animals: Evolution and Sensory Perception. Bulletin of the Seismological Society of America, 90(2), pp. 312-323.
Mott, M., 2003. Can Animals Sense Earthquakes? [online] National Geographic. Available at: <https://www.nationalgeographic.com/animals/2003/11/animals-sense-earthquakes/> [Accessed 19 Oct 2018].
Southern California Earthquake Data Center (SCEDC), 2018. What Happens When an Earthquake Occurs? [online] California Institute of Technology. Available at: <http://scedc.caltech.edu/recent/whathappens.html> [Accessed 19 Oct 2018].
U.S. Geological Survey, 2018. Animals & Earthquake Prediction. [online] U.S. Geological Survey. Available at: <https://earthquake.usgs.gov/learn/topics/animal_eqs.php> [Accessed 19 Oct 2018].
Woith, H., Petersen, G.M., Hainzl, S. and Dahm, T., 2018. Review: Can Animals Predict Earthquakes? Bulletin of the Seismological Society of America, 108(3A), pp. 1031-1045.