When it comes to earthquakes, it's not just the immediate shaking that's a hazard. Massive landslides that are triggered by quakes can do enormous amounts of damage, sweeping houses, cars and trees down hillsides in their wake and burying roads under debris.
But it may not be the immediate quake that created the risk. Scientists have discovered that the changes of a massive landslide occurring in a given location are a lot greater if a previous powerful quake occurred there, even if it was decades before.
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That's the finding of a study by researchers at Great Britain's University of Cardiff, recently published in the journal Earth Surface Dynamics.
"You could think of it as mountains remembering past earthquakes, which affects how they respond to future earthquakes," explained Robert Parker, a Cardiff researcher who is the study's lead author, in a press release.
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To reach their conclusions, the scientists used data from two individual earthquakes that occurred in close-proximity to each other, in 1929 and 1968, on the South Island of New Zealand.
Their results suggested that hillsides in areas that experienced strong ground motions in the 1929 earthquake were more likely to fall during the 1968 earthquake than would be expected on the basis of other factors alone.
The scientists think that the increased likelihood of a landslide may be the result of damage that persists deep inside slopes after the initial quake. That weakness leads the hillside to give way when a second quake occurs.
Parker and his team are now trying to find out whether this ‘memory effect' is seen in other areas, and have begun investigating the earthquakes that occurred in Nepal.
Parker also has designed a computer program called ShakeSlide, which aims to predict areas where landslides will occur after quakes.