3 - Earthquake ground motion and patterns of seismically induced landsliding

Summary

Abstract

Earthquake strong ground motion changes stresses in hillslopes and reduces the strength of surface materials. This can cause landsliding during earthquakes and enhance rates of slope failure in epicentral areas for longer periods. Rates of earthquake-triggered landsliding are strongly correlated with measured peak ground acceleration. Patterns of landslide density reflect the attenuation of seismic waves and geologic and topographic site effects. Using historic thrust fault ruptures with well-documented ground motion and landslide distributions as examples, we illustrate the links between earthquake mechanisms, seismic wave propagation, and triggered landsliding. The examples have shared geomorphic attributes: a maximum density of triggered landslides where earthquake slip is greatest; a progressive decrease of landslide density away from this maximum; clustering of triggered landslides on topographic ridges and other convex landscape elements; and preferential failure of slopes facing away from the earthquake source. We also show that rates of landsliding can remain high after an earthquake in a geomorphic crisis that fades over a period of years. Continued landsliding adds to the total erosion caused by an earthquake, reducing or possibly canceling seismic surface uplift. The examples underline the potential for the quantitative prediction of patterns of seismically triggered and induced landsliding, use of observed landslide patterns for study of earthquake mechanisms, and inclusion of seismically driven erosion in landscape evolution models.