Strategies for Implementing the Traction-Free Condition at the Free-Surface Topography

Session: Numerical Modeling of Rupture Dynamics, Earthquake Ground Motion and Seismic Noise
Type: Oral
Date: 4/29/2020
Time: 09:00 AM
Room: 230 + 235
Description: 

The Earth’s curved free surface can significantly affect the seismic wavefield and earthquake ground motion. Reflection, scattering, conversion, focusing/defocusing and possibly also diffraction can individually or together produce both interesting and important seismic wavefield phenomena including specific phases or induced local waves, amplification/deamplification and differential motion. A topographic feature such as hill or ridge neighboring a sediment basin can considerably affect the earthquake ground motion inside the basin. A specific effect of topography considerably depends on the wavefield-medium configuration and the frequency range.

The finite-difference method (FDM) can very well implement geometrically complicated internal material interfaces on a uniform grid if a proper discrete representation of material heterogeneity, well approximating the interface boundary condition, is used. Implementation of the traction-free condition at a curved free surface is, however, a much more difficult problem.

We compare more than 10 important approaches to implement free-surface topography in FDM modeling. They differ in a) equation formulation, b) spatial grid, c) mapping, d) transformations of the equation of motion, constitutive law, material parameters, wavefield quantities and boundary condition, e) FD approximation of the boundary condition and f) FD scheme. As a consequence, the approaches differ in accuracy, computational time and computational memory.

Presenting Author: Peter Moczo

Authors