Journal of Geophysical Research: Earth Surface

Cover image for Vol. 122 Issue 6

Impact Factor: 3.412

ISI Journal Citation Reports © Ranking: 2016: 33/188 (Geosciences Multidisciplinary)

Online ISSN: 2169-9011

Associated Title(s): Journal of Geophysical Research

Subsurface structure affects landslide susceptibility


The likelihood of landslides on an exposed bedrock hill is dependent on both the strength of the bedrock and the slope of the hill. In general, stronger rocks provide increased resilience against landslides and are capable of supporting steeper slopes. But for the hills of Fiordland and the Southern Alps, regions in New Zealand that experience repeated landslides, these simple proxy measures do not tell the whole story. The hills in these two regions have similar slopes, despite the fact that they are formed from rocks with significantly different inherent strengths, and the landslides in the Southern Alps are both more powerful and more common than those in Fiordland. To find the cause of this disparity, Clarke and Burbank (2011) conducted a series of seismic refraction surveys at numerous sites in both regions to determine the distribution and density of subsurface fractures. They found that at most sites in the Southern Alps, the destabilizing cracks were evenly distributed throughout the bedrock. At the majority of Fiordland sites, however, fracture patterns reveal two distinct subsurface zones: a heavily fractured surface layer in which fracture density diminishes with depth and a uniformly fractured lower layer. According to the authors, the uniform fracturing observed in both the Southern Alps and the lower layer of the Fiordland rock is due to tectonic forces, whereas the more intense fracturing in the surface layer of Fiordland is caused by geomorphic processes focused within the upper few meters of the bedrock. The authors suggest that the dual-layer pattern only develops on hillslopes that remain stable over timescales long enough to allow the geomorphic processes to act. By comparing the tectonically induced fracture densities that delineate between the single- and dual-layer sites in each region, the authors identified the threshold densities above which the bedrock became unstable and susceptible to landslides. The research demonstrates one of the first techniques to relate subsurface structure to landslide occurrence and the potential for a powerful tool in landslide prediction.

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