20 March 2019

Are Animals Earthquake Alerts?

Welcome back. During my government career, I sometimes participated when contractors or others pitched colleagues for research funding. Among a handful of topics discussed at one such session was earthquake prediction by animals
Cartoon on animals predicting earthquakes by T.O. Sylvester (from UNDP. 1992. Introduction to Hazards. Disaster Management Training Programme; obtained from The New Zealand Digital Library, Univ of Walato www.nzdl.org/cgi-bin/library.cgi).
Given our mission, we couldn’t justify offering support, but others have over the years. I’ll give a bit of background and review the latest work.

Anecdotal Reports
Minor details vary with the source, but the earliest account of unusual animal behavior prior to an earthquake traces to ancient Greece. In 373 BC, a variety of animals, insects to rodents and some sources add dogs, reportedly left the city of Helike (or Helice) a day or days before a destructive earthquake.

There have been numerous reports of animals behaving strangely seconds to weeks before an earthquake. Considering the seismic energy produced by earthquakes, no one would doubt that animals might react seconds or minutes before you and I felt any effect. Still, reports of animals responding weeks or even days before our senses are aroused lack explanation and are, thus, hard to accept.

Seismic Waves
Earthquakes generate seismic energy as both body waves that travel through the earth's inner layers and surface waves that move along the earth’s surface.

Body waves are typically higher frequency and lower amplitude than surface waves, and they arrive quicker. The fastest body waves are the primary or P waves that move through solid rock as well as fluids. The slower body waves are the secondary or S waves that move only through solid rock.

Annotated earthquake seismogram (from academic.brooklyn.cuny.edu/geology/grocha/plates/platetec19.htm).
Although body waves arrive before surface waves, the higher amplitude surface waves usually cause most of the damage.

It follows that animals with keener senses would perceive a P wave before the S wave arrives and certainly before surface waves arrive. Yet that’s normally a matter of seconds or minutes, not days or weeks. To establish that animals have the ability to respond long before a significant earthquake occurs would require the discovery of some unknown signal or signals.

Analysis of Animal Behavior Reports

Researchers from the GFZ German Research Centre for Geosciences and University of Potsdam examined 729 reports of abnormal behavior by over 130 animal species before 160 earthquakes. The reported behaviors ranged from seconds to months before the earthquakes, at distances up to hundreds of kilometers from the epicenters, with most occurring within 60 days and 100 km (62 miles).

The researchers’ guidelines for analyzing the reported occurrences included whether the associations between animal behaviors and earthquakes were based on defined rules (e.g., animal's distance from earthquakes of a certain magnitude), if the behavior had ever been observed and not followed by an earthquake, if there was a statistical testing hypothesis in place to examine the evidence and if the animals were healthy.

Study Results
The researchers found that only 14 of the 729 reports recorded a series of observations over time, the longest being one year; all other records were single observations. A long-term record is required to ensure the observations relate to an earthquake and not to some other change, for example, in environment, animal health or predators.

Another hurdle for systematic analysis was the high variability of data, generally anecdotal and retrospective.

A key finding was that abnormal animal behaviors were strongly clustered statistically with foreshocks, suggesting that at least some observed behaviors were likely due to foreshock-generated seismic waves or secondary effects. (Foreshocks and aftershocks are earthquakes that occur before and after the more powerful, main seismic event and that are related to the mainshock in time and space.)

Wrap Up
Overall, the study found the reported data were insufficient to establish that animals exhibit abnormal behaviors before known earthquake effects. To support future experiments, the researchers suggested questions to be assessed to ensure the quality of observations. For example: Is the experimental setup and monitoring procedure clearly described and reproducible? Is it proven that the animal behavior is really unusual?

It’s an interesting topic that’s not fully understood. Thanks for stopping by.

P.S.
Example articles on animals predicting earthquakes:  earthquake.usgs.gov/learn/topics/animal_eqs.php
www.newscientist.com/article/mg19325911-800-when-animals-predict-earthquakes/
www.roger-pearse.com/weblog/2010/07/29/a-myth-take-about-helice-the-earthquake-and-diodorus-siculus/
Background on seismic waves: www.geo.mtu.edu/UPSeis/waves.html 

Study of reports of animal behavior before earthquakes in Bulletin of the Seismological Society of America: pubs.geoscienceworld.org/ssa/bssa/article-abstract/530275/
Articles on study on LiveScience and ScienceDaily websites:
www.livescience.com/32156-can-animals-predict-earthquakes.html
www.sciencedaily.com/releases/2018/04/180417115641.htm

A version of this blog post appeared earlier on www.warrensnotice.com.

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