Mainshocks are usually followed by aftershocks. Aftershocks continue over a period of time with a decreasing frequency and there is not sufficient time for repair and retrofit between a mainshock – aftershock sequence. Typically, aftershocks are smaller in magnitude; however, aftershock ground motion characteristics such as the intensity and duration can be greater than the mainshock due to the changes in the earthquake mechanism and location with respect to the site. The seismic performance of slopes is typically evaluated based on the sliding displacement predicted to occur along a critical sliding surface. Various empirical models are available that predict sliding displacement as a function of seismic loading, ground motion, and site parameters but these models do not include the aftershocks. Seismic risks associated with the post-mainshock slopes (“Damaged slopes”) subjected to aftershocks are significant. This study extends the empirical sliding displacement models for flexible slopes subjected to earthquake mainshock – aftershock sequences (a multi hazard approach). A comprehensive dataset was developed using 144 pairs of as-recorded mainshock – aftershock sequences using Pacific Earthquake Engineering Research (PEER) database. The predictive models are functions of seismic loading, ground motion, site, and slope parameters. The results revealed that decoupled sliding displacements of post-mainshock slopes subjected to aftershocks increased on average around 30% at all site periods due to the combined effects of strength degradation and additional seismic demand by the aftershock. A case study is demonstrated to explain the effects of aftershocks on the seismic performance of post-mainshock flexible sliding masses. Overall, the results suggest that aftershocks increase the seismic demand relative to the mainshock alone; thus, the seismic risk is underestimated if aftershocks are neglected.

Date of publication

Fall 4-16-2019

Document Type




Persistent identifier


Committee members

Dr. Gokhan Saygili, Dr. Torey Nalbone, Dr. Micheal Gangone


Master of Science in Civil Engineering