Seismic precursor to instability induced by internal erosion in loose granular slopes

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

“…Pore pressures keep actually increasing at middepth during the movement, suggesting contractive behavior conducive to long runout (as demonstrated numerically by Iverson & George, ). Consistently with what observed by Hu et al (), to whom the reader is referred to for additional details and examples, the intensity of the vibration recorded at the slope floor increases seconds before failure, and before any macroscopic deformation or pore pressure spike is recorded. Figures d and f show an estimation of the total hydraulic head at various locations at different times, under the simplifying assumption of hydrostatic pressure gradient.…”

“…Mixtures of sand with silt‐sized particles produce different modes of motion related to the different ability to dissipate the pore pressure excess (G. Wang & Sassa, , ). Investigations on loose artificial slopes (Hu et al, , ) showed pore pressure buildup upon failure—positively correlated with the proportion of small particles—but without macroscopic vanishing of effective stresses. Seismic vibrations were found to occur before macroscopic pore pressure spikes and displacements (Hu et al, ), which were related to structural changes caused by seepage‐induced migration of small grains.…”

“…Investigations on loose artificial slopes (Hu et al, , ) showed pore pressure buildup upon failure—positively correlated with the proportion of small particles—but without macroscopic vanishing of effective stresses. Seismic vibrations were found to occur before macroscopic pore pressure spikes and displacements (Hu et al, ), which were related to structural changes caused by seepage‐induced migration of small grains. Similarly, high‐frequency acoustic emissions were shown to precede the instability propagation and global failure (Jiang et al, ).…”

Earthquake‐Induced Chains of Geologic Hazards: Patterns, Mechanisms, and Impacts

“…Active landslides tend to shed debris flows along narrow gullies, partly via Hortonian overland flow driving sediment entrainment (e.g., Domènech et al, ; van Asch et al, ) or collapse of water‐saturated landslide material (Iverson, ). Experiments on artificial slopes using debris from coseismic landslides provide insight into how changes to grain‐size distributions of landslide debris affect the initiation and runout of flow‐like landslides (Hu et al, ; Hu, Hicher, et al, ; Hu, Scaringi, et al, ; Wang & Sassa, , ). These studies pointed out that hydrologically driven grain coarsening, for example, through surficial and internal erosion and depletion of fine particles, can improve the stability condition of the deposits by increasing their hydraulic conductivity and intergranular contacts, reducing the probability of failure in larger rainstorms (Hu et al, ; Hu, Hicher, et al, ).…”

“…Third, vegetation can quickly reclaim slopes denuded by earthquakes, particularly in humid tropical and temperate regions, thus reducing overland flow and stabilizing hillslopes by root anchoring (e.g., O'Loughlin, ; Schmidt et al, ; Watson et al, ) and eventually shutting down potential sediment sources for debris flows (Y. Liu, Liu, & Ge, ). Fourth, grain coarsening resulting from progressive winnowing of fines or recurring landsliding (Hu, Hicher, et al, ; Hu, Scaringi, et al, ; S. Zhang, Zhang, & Chen, ) increases hydraulic conductivity, making surface runoff and excess pore pressure less likely. A measured spike in suspended sediment concentrations (grain size < 0.25–0.5 mm) in rivers soon after the Wenchuan earthquake, followed by a decay in subsequent years (Li et al, ; J. Wang, Jin, et al, ; Wang et al, ), might be some evidence of this coarsening process or simply reflect artifacts of debris flow (S. Zhang et al, ).…”