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Study Sheds Light On Relationship Between Earthquakes And Landslides

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When an earthquake occurs in a mountainous region, one thing people prepare themselves for is a landslide.

It may seem obvious for an earthquake to cause a landslide, but what makes the effects of an earthquake to a landslide unique from other natural events that may cause it?

"The main difficulty was one must distinguish between the meteorological and the seismic causes of land sliding," said Marc Odin, a scientist at GFZ.

In a new study conducted by an international team of geoscientists lead by the GFZ German Research Centre, German, French and Japanese scientists found that after an earthquake has subsided, no matter how strong it is, landslide activity may return to its background level as it was before within one to four years. Findings were published online in the journal Geology.

"Heavy rain can produce landslides and can enhance landslides after an earthquake," added Odin, who is also the study's lead author.

In their study, the researchers looked at areas that were affected by landslides caused by four earthquakes measured between 6.6 and 7.6 on the Richter scale, or moderate to severe quakes. The researchers noted two interacting processes in the event - a strong earthquake that loosens up the layer of soil from the underlying bedrock, also damaging it, and water seeping into the cracks that open up due to the earthquake serving as a "lubricating film" where the slope of the mountain slides right into the valley.

"We analytically separated the effect of the rain from the seismic activity and so were able to determine that the decrease of landslides through time is based on an internal healing process of the landscape," explained Odin. The researchers found that depending on the weather, the rocks around and below the area and the magnitude of the earthquake, landslides gradually recover. It could take as quick as a month to longer years, but a landslide will eventually return to how it was before the earthquake activity. Over time, sand and earth fill in the cracks, and they close again.

With the discovery of the effects of earthquakes to landslides that eventually self-heal, the team of geoscientists confirm their current studies being conducted in the Himalayas. They are modeling the geological effects of the devastating earthquakes that shook the soils of Nepal this year. 

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