Animals may sense chemical changes in groundwater that occur when an earthquake is about to strike.
This, scientists say, could be the cause of bizarre earthquake-associated animal behaviour.
Researchers began to investigate these chemical effects after seeing a colony of toads abandon its pond in L’Aquila, Italy, in 2009 – days before a quake.
They suggest that animal behaviour could be incorporated into earthquake forecasting.
The team’s findings are published in the International Journal of Environmental Research and Public Health. In this paper, they describe a mechanism whereby stressed rocks in the Earth’s crust release charged particles that react with the groundwater.
Animals that live in or near groundwater are highly sensitive to any changes in its chemistry, so they might sense this days before the rocks finally “slip” and cause a quake.
The team, led by Friedemann Freund from Nasa and Rachel Grant from the UK’s Open University hope their hypothesis will inspire biologists and geologists to work together, to find out exactly how animals might help us recognise some of the elusive signs of an imminent earthquake.
The L’Aquila toads are not the first example of strange animal behaviour before a major seismic event. There have been reports throughout history of reptiles, amphibians and fish behaving in unusual ways just before an earthquake struck.
In 1975, in Haicheng, China, for example, many people spotted snakes emerging from their burrows a month before the city was hit by
a large earthquake.
This was particularly odd, because it occurred during the winter. The snakes were in the middle of their annual hibernation, and with temperatures well below freezing, venturing outside was suicide for the cold-blooded reptiles.
But each of these cases – of waking reptiles, fleeing amphibians or deep-sea fish rising to the surface – has been an individual anecdote. And major earthquakes are so rare that the events surrounding them are almost impossible to study in detail.
This is where the case of the L’Aquila toads was different.
Ms Grant, a biologist from the Open University, was monitoring the toad colony as part of her PhD project.
“It was very dramatic,” she recalled. “It went from 96 toads to almost zero over three days.”