Fault Rupture Propagation through Previously Ruptured Soil

Abstract

Surface fault rupture during recent earthquakes has significantly damaged structures. Although several researchers have studied surface fault rupture, the effects of fault rupture propagating through soil that has been ruptured previously have not been investigated. Yet, faults rupture multiple times so that native soil deposits will have likely undergone previous ruptures that would have developed shear bands within the soil, and the stress state of the soil will have evolved because of these events. In addition, the predominant modes of soil shearing during the fault rupture process have not been characterized fully. Numerical simulations are performed to analyze the mechanics of dip-slip surface fault rupture and to explore the effects of previously ruptured soil. The numerical results demonstrate that the soil rupture process occurs in two distinct stages. First, broad deformation occurs before strain localization, which is followed by more localized deformation after shear band formation. Stress paths in the rupture zone are analogous to plane-strain extension (loading) and plane-strain compression (unloading) element tests for reverse and normal faults, respectively. The performance of structures significantly depends on whether the soil has been ruptured previously.