Past earthquakes can make landslides more likely

A road being cleared on May 10, 2015, after an earthquake in Sindhupalchok district, Nepal. (Credit: Asian Development Bank/Flickr)

Places that have experienced strong earthquakes in the past may be more likely to produce landslides if a second earthquake strikes, a new study finds.

These new insights could have important implications for disaster management and could help experts identify areas that may be susceptible to future landslides.

Current models used to assess the likelihood of landslides do not consider historical occurrences of earthquakes, and instead focus on the strength of the earthquake and the characteristics of the particular area, including the makeup of rock and the steepness of slopes.

“This could potentially be a significant gap in our understanding of the factors that lead to landsliding,” says Robert Parker from Cardiff University’s School of Earth and Ocean Sciences. Parker is lead author of the study published in the journal Earth Surface Dynamics.

Parker and colleague analyzed data from two individual earthquakes that occurred in close-proximity to each other, in 1929 and 1968, on the South Island of New Zealand. The epicenters of the two earthquakes were around 21 kilometers (13 miles) apart and both triggered landslides over a large area.

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They first examined the influence that standard factors—such as the strength of the earthquake and the gradient of hillslopes—had on the distribution of landslides. They also investigated whether the results could be attributed to the legacy of previous events.

The results suggest that hillslopes in regions that experienced strong ground motions in the 1929 earthquake were more likely to fail during the 1968 earthquake than would be expected on the basis of the standard factors alone.

“Our results suggest that areas that experienced strong shaking in the first earthquake were more likely to produce landslides in the second earthquake than would be expected based on the strength of shaking and hillslope characteristics alone,” says Parker.

“Strong shaking in a past earthquake may actually cause mountains to be more hazardous, in terms of landslides, in a future earthquake many years or decades later. You could think of it as mountains remembering past earthquakes, which affects how they respond to future earthquakes.”

Parker and his team are now investigating whether this “memory effect” is seen in other areas, and have begun investigating the earthquakes that occurred in Nepal.

Researchers from the University of East Anglia, Durham University, and the Institute of Geological and Nuclear Sciences, New Zealand, collaborated on the project.

Source: Cardiff University