Effect of Amplitude and Duration of Cyclic Loading on Frictional Sliding Instability in Granular Media: Implication to Earthquake Triggering of Landslides

Strong earthquakes with larger magnitude and longer durations trigger many landslides, however, how magnitude and duration affect landslides is still unclear. Many factors could contribute to this, including additional shear stress provided by strong ground motion, or "seismogenic liquefaction"; herein, we hypothesize that the dynamic weakening of sliding zone gouge is important. We explored the influence of earthquake magnitude and duration on landslide triggering by simulating the seismic response of sliding zone gouge using a dynamic ring-shear device and glass spheres. The experiments showed that vibration with larger amplitudes and longer durations more easily trigger deformation and even instability in dry granular materials. We used a dynamic triaxial-bender system to find that the shear modulus of these materials decreased with the increase in duration and amplitude of cyclic loading. We suggest that this universal decrease in shear modulus is an important landslide-trigger mechanism. Our results revealed how magnitude and duration of earthquakes affect co-seismic landslides and why earthquakes with larger magnitude and long durations can trigger more co-seismic landslides.