The Impact of Material Stiffness on the Likelihood of Fault Rupture Propagating to the Ground Surface

Abstract

Online Material: Tabulation of reverse and strike slip events. The stiffness of the upper thirty meters of geologic material is shown statistically to have a strong impact on the propagation of fault rupture at depth to the ground surface for reverse events. The stiffness of a geologic material controls its capacity for absorbing or transmitting discrete localized planar deformations. However, the fault mechanism that initiated the deformations and the resulting stress state also has an influence. This can be seen in how the stiffness of the upper thirty meters has no impact on the propagation of fault rupture at depth to the ground surface in strike‐slip events. An empirical database of past earthquakes that did and did not result in surface fault rupture, along with bulk estimates of the stiffness of near‐surface geologic materials using V S 30 (thirty‐meter shear‐wave velocity) is presented. The probability of fault rupture reaching the ground surface is estimated from this database using logistic regression. These unique results, which are a function of the fault mechanism and near‐surface stiffness, are explained in a mechanistic framework. The regression results provide a means of estimating the likelihood of surface fault rupture for reverse events given the near‐surface stiffness, and may also provide a path forward when engineering against the same. The working hypothesis for this research is that both the faulting mechanism and the near‐surface stiffness of geologic material influence the likelihood of fault rupture propagating from seismogenic depth to the ground surface. Reverse faulting results in a different failure mechanism in near‐surface geologic material than does strike‐slip faulting. This research is a byproduct of research into probabilistic fault‐displacement hazard analysis summarized in Moss and Ross (2011). In that work we quantified the likelihood of fault rupture propagating to the surface based solely on faulting mechanism. …