Effect of a compliant fault zone on the inferred earthquake slip distribution

Sylvain D. Barbot, Yuri Fialko, & David T. Sandwell

Published 2008, SCEC Contribution #1271

We present a new semi-analytic method to evaluate the deformation due to a screw dislocation in arbitrarily heterogeneous and/or anisotropic elastic half-plane. The method employs integral transformations to reduce the governing partial differential equations to the integral Fredholm equation of the second kind. Dislocation sources, as well as spatial perturbations in the elastic properties are modeled using equivalent body forces. The solution to the Fredholm equation is obtained in the Fourier domain using a method of successive over-relaxation, and is mapped into the spatial domain using
the inverse Fast Fourier Transform. We apply this method to
investigate the effect of a soft damage zone around an earthquake fault on the co-seismic displacement field, and on the earthquake slip distribution inferred from inversions of geodetic data. In the presence of a kilometer-wide damage zone with the reduction of the
effective shear modulus of a factor of 2, inversions that assume a
laterally homogeneous model tend to underestimate the amount of slip
in the middle of the seismogenic layer by as much as 20\%. This bias
may accentuate the inferred maxima in the seismic moment release at
depth between 3-6 km suggested by previous studies of large
strike-slip earthquakes.

Key Words
elasticity, numerical models, seismic moment, data processing, damage, elastic constants, strike-slip faults, displacements, deformation, depth, seismic zoning, fast Fourier transforms, Fourier analysis, Fredholm equation, lateral heterogeneity, shear modulus, earthquakes, accuracy, faults, anisotropy, fault zones

Barbot, S. D., Fialko, Y., & Sandwell, D. T. (2008). Effect of a compliant fault zone on the inferred earthquake slip distribution. Journal of Geophysical Research, 113, B06404.