Unexpected quakes may be ancient aftershocks
Thursday November 05 2009
SOME OF the most violent earthquakes that have occurred unexpectedly in places with no recent record of tremors may be the aftershocks of earthquakes that took place decades or even centuries ago, scientists have discovered.
The finding could explain many unexpected earthquakes that hit the centre of continental shelves, such as the disastrous quake in Sichuan in the heart of China in May 2008, which killed at least 68,000 people and injured up to 400,000 more. At 7.9 on the Richter scale, it was one of the most deadly quakes in history.
Earthquakes usually occur at the boundary of two or more tectonic plates. But they can also occur many hundreds of miles from a fault line.
A laboratory study that tested how tectonic faults work has found that the further away an earthquake is from such faultlines, the stronger the likelihood it could be the long aftershock of a previous earthquake.
The research may help to predict when and where an earthquake is likely, said Professor Seth Stein at Northwestern University. "We need to use methods like GPS satellites and computer modelling to look for places where the earth is storing up energy for a large future earthquake," Mr Stein said. (©Independent News Service)
Irish Independent
