Rain makes the ground shake

A wet weekend may be enough to set off an earthquake.

A spate of rain is all it takes to set off some earthquakes. That's what a team of German geologists has discovered after monitoring swarms of tiny tremors in the mountains of Bavaria.

Sebastian Hainzl of the University of Potsdam and his colleagues say that the rise in water pressure within porous rocks as rain soaks into the ground can start quakes on hair-trigger faults. "Tiny changes can have big effects," says Hainzl's coworker Toni Kraft of Ludwig-Maximilians University in Munich.

The idea that changes in pore-water pressure can induce earthquakes is well established. And seismic activity can be seasonal, perhaps because of rainfall variations.

But the link has never been firmly established, and it was generally thought that much larger water flows are needed than those produced by rainfall.

Reservoir filling can trigger quakes, for example, either because of the weight of water or its permeation into the rock. One of the most notorious examples happened in 1967 in western India, where the reservoir created by the Koyna Dam, completed in 1962, is thought to have caused a magnitude-7 quake that killed 200 people.



[link to www.nature.com]