Near-Field Across-Fault Seismic Ground Motions

Abstract

Abstract There are many engineering applications that require an understanding of the nature of strong ground motions adjacent to and spanning across faults. Unfortunately, such near-field observations at distances less than 100 m of fault rupture are few and incomplete. In this study a 3D finite-difference method is used to simulate strong ground motions for a hypothetical M w  6.5 earthquake at sites within a few tens of meters of the fault to document the nature of strong ground motion at pairs of sites across the fault as a first step toward providing ground-motion input for engineering design applications. We employ several distributed slip kinematic models to examine ground-motion variability. We also examine the ground motions for fault scenarios ranging from vertical strike-slip to low-angle thrust faulting. The results show that the motions have two primary components: (1) far-field waves that undergo focusing and amplification due to finite-source rupture directivity and (2) near-field waves that are sensitive to the tectonic rebound, or fling, of the closest section of the fault to the recording stations. Both the far-field and near-field controlled motions result in nonstationary pulse-like velocity waveforms that have many implications for the design of engineered structures located close to or spanning faults.