The control of earthquake sequences on hillslope stability

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 mechanisms that control hillslope stability in response to ground shaking are poorly constrained in ductile hillslope materials, 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.