The control of earthquake sequences on hillslope stability

Abstract

Earthquakes trigger landslides in mountainous regions. Recent research suggests that the stability of hillslopes during and after a large earthquake is influenced by legacy effects of previous seismic activity. However, the shear strength and strain response of ductile hillslope materials to sequences of earthquake ground shaking of varying character is poorly constrained, inhibiting our ability to fully explain the nature of earthquake‐triggered landslides. We used geotechnical laboratory testing to simulate earthquake loading of hillslopes and to assess how different sequences of ground shaking influence hillslope stability prior to, during, and following an earthquake mainshock. Ground‐shaking events prior to a mainshock that do not result in high landslide strain accumulation can increase bulk density and interparticle friction. This strengthens a hillslope, reducing landslide displacement during subsequent seismicity. By implication, landscapes in different tectonic settings will likely demonstrate different short‐ and long‐term responses to single earthquakes due to differences in the magnitude, frequency, and sequencing of earthquakes.

Spatial prediction of earthquake-induced landslide probability

“…Marc et al (2016) handled this problem similarly, by applying a constant material sensitivity parameter and 20 hypothesising a variety of mechanisms by which unconstrained material control may have influenced outlier events, while Gallen et al (2016) dealt with this uncertainty by exploring a range of probable material properties. Through the alternative method presented here, our analysis derives similar outcomes; primarily that there is a general behaviour common to all the earthquakes tested here, and that departures from that general behaviour appear to relate to spatial, and perhaps temporal (Brain et al, 2017;Parker et al, 2015), variations in material control on landscape response. 25…”

“…Brain et al (2017) proposed that low magnitude earthquakes drive the consolidation and stabilisation of hillslope materials, during periods intervening large earthquakes, while Parker et al (2015) suggested that accrued brittle damage can leave unfailed hillslopes at greater susceptibility to failure following large earthquakes. Samia et al (2017) have suggested that the occurrence of landslides destabilises hillslopes more widely, resulting in greater susceptibility for follow-up landslides over a period of about 10 years.…”

Internal Erosion Controls Failure and Runout of Loose Granular Deposits: Evidence From Flume Tests and Implications for Postseismic Slope Healing

“…This seems reasonable because (1) soils rich in small particles have smaller global void ratios, e , and hence less room for compaction, unless more room is provided through internal erosion; and (2) they are subjected to smaller seepage forces, due to their much lower k , which may be insufficient to force rearrangements of the coarse grains. These processes, however, may well occur in coarse‐only assemblies (although they may require much stronger, thus less probable, hydrological inputs, and hydraulic gradients) and may occur in any case if promoted by seismicity (see Brain et al, ).…”

Laboratory simulations of rainfall-induced landslide reactivation mechanisms following the 2016 Kaikōura Earthquake

“…This densificaiton and strengthening behavior has been observed in previous studies within normally consolidated materials e.g. (Carey et al, 2021, Brain et al, 2017and Take et al, 2004 demonstrating sample strengthening through dynamic stress inputs (e.g. earthquake simulations).…”

“…Contrary to this, Brain et al (2017) conducted tests using a dynamic back-pressured shearbox to simulate earthquake ground shaking on ductile hillslope material. They conclude that ground-shaking events before the main aftershock that do not cause landslide strain accumulation, can result in increases in bulk density and inter-particle friction.…”