On the seismic response of deep-seated rock slope instabilities - Insights from numerical modeling

Earthquake-induced landslides constitute a critical component of seismic hazard in mountainous regions, While many seismic slope stability analysis methods exist with varying degrees of complexity, details of interactions between seismic waves and incipient landslides are not well understood and rarely incorporated, in particular for deep-seated slope instabilities. We present a series of 2D distinct-element numerical models aimed at clarifying interactions between earthquakes and large rock lope instabilities. The study has two main goals: 1) to explore the role of amplification in enhancing co-seismic slope deformation - a relationship widely discussed in literature but rarely tested quantitatively; and 2) to compare our numerical results with the well-established Newmark-method, which is commonly used in seismic slope stability analysis. We focus on three amplification phenomena: 1) geometric (topographic) amplification, 2) amplification related to material contrasts, and 3) amplification related to compliant fractures. Slope height, topography, seismic velocity contrasts, and internal strength and damage history were varied systematically in a series of models with a relatively simple, scalable geometry. For each model, we compute the spatial amplification patterns and displacement induced by real earthquake ground motions. We find that material contrasts and internal fracturing create both the largest amplification factors and induced displacements, while the effect of geometry is comparably small. Newmark-type sliding block methods underestimate displacements by not accounting for material contrasts and internal fracturing within the landslide body both common phenomena in deep-seated slope instabilities. Although larger amplification factors tend to be associated with greater displacements, we did not identify a clear link between ground motion frequency content, spectral amplification, and induced displacement Nevertheless, observation of amplification patterns can play an important role in seismic slope stability analyses, as: 1) strong amplification (related to material contrasts or compliant fractures) is an indicator of potentially large co-seismic displacements; and 2) amplification patterns can be used to constrain geological and numerical models used for seismic stability analysis. The complexity of wave-slope interactions, as well as the potential to severely underestimate hazard using Newmark-type methods, motivates use of rigorous numerical modeling for quantitative seismic hazard and risk assessment of large landslides. (C) 2015 Elsevier B.V. All rights reserved.