Movement of landslides caused by earthquakes

The Landslide blog is written by Dave Beatley, widely recognized as a world leader in the study and management of landslides.

The main determining factor of a landslide's ability to cause loss is its movement. More mobile landslides have a greater potential to impact people and their assets, and faster movement can cause greater damage. However, assessing mobility for expected failure is very difficult. It is not surprising then that this has been a major topic of research.

Huge debris pile resulting from the large landslide movement caused by the 2008 Wenchuan earthquake.

In general, it is accepted that larger landslides are more mobile than smaller landslides, and that mobility scales with size. This is not just a function of the larger volume having the ability to cover a larger area, but in fact the coefficient of friction decreases with the size of the landslide (in general). There is a lot of speculation, but little conclusive evidence as to why this is, but the effect is clearly evident.

There is a really interesting contribution to this debate (Grant and Culhane 2024) which has just been published in the Journal of Engineering Geology. In this study, the authors examined 23 landslide stocks for large earthquakes to examine the runoff characteristics of coseismic landslides. Inventories have been collected and published online by others, but this investigation was by no means a trivial task, as the authors had to find an automated way to assess the runoff distance for each of the 73,665 landslides in the collected data set.

There are two real surprises in the results. The first is that the movement of landslides caused by earthquakes is different from the movement of landslides caused by other events (such as rainfall). For smaller landslides, motion varies with size, although there is greater variability than is the case for other triggers. In essence, seismic landslide motion is more complex (and therefore less predictable), which is not good news for those of us trying to assess landslide risks for future earthquakes.

The second, more surprising, is that the movement of cosmic landslides is bilinear. In other words, after a certain magnitude threshold, the movement of earthquake-induced landslides decreases (rather than increases) as a general trend. Calling this a surprise is an understatement.

The reasons why earthquake-induced landslide movement differs from those associated with other triggers need further investigation. Grant and Culhane (2024) suggest that it will be related to “landslide type, kinematics, hydrology, and/or differences in setting… which vary systematically between different triggering mechanisms.”

They concluded that new models of landslide movement in earthquake events are needed, but of course this will require further research. I suspect this will be a major area of ​​interest in the coming years.

Assessing landslide risks from seismic events has become a bit more difficult, but my word is that this is interesting research. Bravo to Grant and Culhane (2024).

reference

Grant, ARR and Culhane, NK 2024. Global patterns of seismic landslide movement differ from aseismic landslide trends. Engineering Geology, 107824, https://doi.org/10.1016/j.enggeo.2024.107824.

Text © 2023. The Authors. CC BY-NC-ND 3.0 Unless otherwise noted, images are subject to copyright. Any reuse without express permission of the copyright owner is prohibited.

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