On a decomposition of near-source earthquake ground motion

Abstract

The characteristics of the near-source ground motion in two-dimensional anti-plane and plane-strain kinematic fault models are examined in some detail. In particular, the relative importance of the near-source starting phases, passage of the rupture front phase and stopping phases is determined. At short distances to the fault, at low or intermediate frequencies, and, away from the ends of the fault, the rupture passage phase dominates the synthetic motion. It is shown that this phase can be calculated by use of a simple steady-state dislocation model. A method of solution which decomposes the near-source ground motion into starting, stopping and rupture passage phases is also presented. Finally, a simple steady-state anti-plane shear fault model in a two-material medium is used to determine the amplification effects associated with shock waves refracted into softer materials.