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Earthquake and Later Effects: More About Delay-Effect Landslides

Aug 25, 2015 06:32 PM EDT
Landslides are likely not caused by rain, but by pre-existing damage from earthquakes or other disruptions.
Months or years after an earthquake, the ground and rocks usually return to a normal state of stability, researchers say.

(Photo : Geology and "Transient changes of landslide rates after earthquakes" by O. Marc et al. Photo by Bhairab Sitaula.)

Large earthquakes really shake up the earth, we know--but they also leave it ready to tilt over into a landslide after certain heavy rains. So, in the wake of the Nepal earthquake, there are concerns that monsoon rainfall conditions will cause the earth to slide and collapse. 

While very little is known about the history of earthquakes on steep, unstable hillslopes, Odin Marc, from the German Research Center for Geosciences, and his colleagues recently published a study in Geology regarding the rock damage caused by the quakes, not the rain. 

In their study, the scientists reconstructed the history of landsliding in four mountain areas that were hit by large, shallow earthquakes. They did this by using a dense time series of satellite images and air photos. Their reconstructions explained that the rate of landsliding caused by rainfall is increased up to 20-fold after an earthquake. However, the reconstructions showed that the area recovers over a period of months to years, as a release noted.

The magnitude of this response and the duration of the recovery phase are possibly related to the size of the earthquake. The researchers also found that heightened landslide rates and their gradual decrease are due to shaking-induced damage of rocks along Earth's surface, the release said. 

That is, in mountainous areas intensely shaken by large earthquakes, higher-than-normal landslide risks are expected during the recovery and rebuilding phase, although conditions return to pre-earthquake levels eventually. 

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