A curved-grid velocity-stress formulation for viscoelastic wave modeling is used with an arbitrary number of relaxation mechanisms to model a desired [Formula: see text]-behavior. These equations are discretized by high-order staggered finite differences (FDs) in the interior of the medium, and we gradually reduce the FD order to two at the stress-free surface, where we implement our boundary conditions for an arbitrary topographic surface. A moving source is simulated along the surface of a relatively general and locally steep surface topography and, for comparison, along a plane surface. The topography consists of a significant hill surrounded by a valley. Similar two-layered geologic models are used with both topographic surfaces, with the upper layer being a lossy sedimentary layer having a relatively strong contrast with the lower, higher-velocity half-space. Local topographic highs create varying amplitude amplifications at different times during motion of the source. A pronounced wavefield accumulation is evident at the topographic highs in all components. This is very different from the even pattern produced by the same source along the same path for the plane topographic surface, even in the presence of the strong material discontinuity between the two geologic layers. The effect is, however, similar to real records for nonmoving sources of long duration; over time, the direction of incidence becomes less significant, and amplitude amplification occurs in all directions for waves trapped in a topographic high. These spatial focusing effects should be taken into account in inversion for vehicle tracking to avoid target mislocation and/or misidentification.
NUMERICAL EVALUATION ON LOAD CARRYING CAPACITIES OF STEEL BRIDGE PIERS DURING LONG DURATION TIME MOTIONS
