Weather affects timing of some natural hazards
Seasonal patterns in earthquakes and volcanic eruptions can be linked to rain and snowBy Devin Powell and Alexandra Witze
Web edition : 5:02 pm
SAN FRANCISCO — If you want to know the chance of an earthquake in the Himalayas or a volcanic eruption in Iceland, check the calendar. Seasonal patterns of rainfall and snowfall can affect how often quakes and volcanoes go off, scientists reported December 8 at a meeting of the American Geophysical Union.
In the Himalayas, the weight of water from monsoon rains helps dampen seismicity for a few months each year, says geophysicist Thomas Ader of Caltech. Seismic records collected from 1998 to 2004 show that the number of quakes drops in the rainy summer months and rebounds when things dry out.
Water from monsoon storms runs off the mountains and into India, where its weight bends the Earth’s crust slightly. From season to season, this bending causes the surface to move back and forth, as recorded by Global Positioning System stations, in time with the rise and fall in earthquake frequency.
Calculations by Ader and his colleagues suggest that the flexing eases the stress on the fault where two tectonic plates collide beneath the Himalayas. This change in stress is quite small — less than a hundred-thousandth of the stress caused by the motion of the plates. But it lasts for months, perhaps giving the earthquakes time to slowly incubate.