Science & technologyMar 28th 2015 edition

Predicting earthquakes
The chickens are restless

Animals really may be able to sense when a tremor is about to happen

SEISMOLOGISTS tend to greet the idea that some animals know when an earthquake is coming with a sizeable degree of scepticism. Though reports of odd animal behaviour before a quake date back at least as far as ancient Greece, the data are all anecdotal. They are also subject to vagaries of the human psyche: “confirmation bias” ensures that strange behaviour not followed by earthquakes gets forgotten, and “flashbulb memory” can, should an earthquake strike, imbue quotidian animal antics with great import after the fact. The US Geological Survey—arguably the world’s authority on earthquakes—undertook studies in the 1970s to find out if animals really did predict them, but came up empty-handed. However, the latest data, just published in Physics and Chemistry of the Earth, are not just anecdotal.

Friedemann Freund of San Jose State University, in California, and his colleagues considered the earthquake of magnitude seven that hit north-eastern Peru in August 2011. They found that, by coincidence, the nearby Yanachaga National Park had in the month running up to the quake been using nine so-called camera traps. These are employed to track the movements of rare or skittish animals, silently snapping pictures (for example, that above, of a paca) when motion sensors are triggered.

Well ahead of the tremor, the traps recorded up to 18 animals a day, but that number began to drop off steeply as the earthquake approached. In the five days immediately before it, the traps snapped just three animals. The park’s fauna, it seems, had stopped moving around.

Dr Freund believes that what animals sense before earthquakes is airborne electric charge. The idea is that the subterranean grinding of stressed rock which precedes a quake stores charge (not unlike that built up by scuffing shoes across a carpet), some of which then flows to the surface, where it ionises molecules in the air. The varying electric field involved in this phenomenon should be detectable from afar.

The team therefore studied data from two very-low-frequency (VLF) receiving stations in Peru, looking for perturbations of the signals. Sure enough, large disturbances occurred in the two weeks prior to the quake.

The correlation of these several facts is, of course, no guarantee of causation. Dr Freund will have his work cut out to persuade the wider world that what the VLF receiver detects is what animals are sensing, and that it is indicative of an impending quake. But he now has something concrete to work with. It may yet turn out that for millennia, furry and feathery forecasters really were trying to tell human beings something.

This article appeared in the Science & technology section of the print edition under the headline "The chickens are restless"

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