Controls on Post‐Seismic Landslide Behavior in Brittle Rocks

Matthew J Brain,Sebastian Moya,Sergio A Sepúlveda,Neil Tunstall,David N Petley,Mark E Kincey

doi:10.1029/2021jf006242

Abstract

AbstractEarthquakes trigger widespread landsliding in tectonically active landscapes. The effects of strong ground shaking on hillslope stability persist into the post‐seismic stage; rates of landsliding remain elevated in the years following an earthquake. The mechanisms that control the spatial pattern and rate of ongoing landsliding are poorly constrained, hindering our ability to reliably forecast how landscapes and landslide hazard evolve. To address this, we undertook a detailed geotechnical investigation in which we subjected representative rock samples to dynamic loading, simulating the effects of earthquake ground shaking on hillslopes of different configuration. Our results indicate that post‐seismic hillslope strength is not an intrinsic rock property; rather, it responds to the amplitude of imposed dynamic loads and the degree of pre‐existing shear surface formation within the rock. This path‐dependent behavior results from differences in the character of fractures generated by dynamic loads of different amplitude, and the ways in which apertures are mobilized or degraded in subsequent (post‐seismic) shearing. Sensitivity to dynamic loading amplitude is greater in shallow landslides in which shear surfaces are yet to fully form; such hillslopes can be strengthened or weakened by earthquake events, depending on their characteristics. In contrast, deeper landslides on steeper hillslopes in which shear surfaces have largely developed are less likely to display differences in behavior in response to dynamic loading because strain accumulation along pre‐existing fractures is dominant. Our results demonstrate the need to consider path‐dependent hillslope stability in numerical models used to forecast how landscapes respond to earthquakes and how post‐seismic hazard evolves.

Highlights

Seismic ground accelerations trigger large numbers of landslides in tectonically active, mountainous landscapes (Keefer, 1984; Parker et al, 2011; Roback et al, 2018)
Our results indicate that post-seismic hillslope strength is not an intrinsic rock property; rather, it responds to the amplitude of imposed dynamic loads and the degree of pre-existing shear surface formation within the rock
We considered how the strength and rheology of rocks can vary in the post-seismic phase in response to dynamic loading that varies in character

Summary

Introduction

Seismic ground accelerations trigger large numbers of landslides in tectonically active, mountainous landscapes (Keefer, 1984; Parker et al, 2011; Roback et al, 2018). These coseismic slope failures, and the resultant release of large volumes of sediment into steep mountain catchments, have a significant effect on the geomorphic evolution of seismically active mountain regions (Croissant et al, 2019; Fan et al, 2018; Wang et al, 2015). The mechanisms responsible for the latter are poorly constrained but have been postulated to result from a range of “healing” processes that include the re-establishment of plant-root cohesion (e.g., Jacoby, 1997; Yunus et al, 2020) and the reversal of dilation experienced during an earthquake as rock and soil masses settle and re-establish frictional contacts (e.g., Lawrence et al, 2009)

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