Three-dimensional modeling of near-fault ground motions with nonplanar rupture models and topography: Case of the 2004 Parkfield earthquake

We study the applicability of deterministic strong ground motion simulations at very near-fault distances for a subvertical strike slip fault model corresponding to the 2004 M6 Parkfield, California, earthquake. Theoretical modeling based on such a model under the assumptions of a planar rupture and 1-D medium show that, as a consequence of the S-wave radiation pattern, the particle motion for such close stations should be almost linear in the fault-normal direction, having fault-parallel (FP) and vertical (V) components almost zero. However, as shown on the Parkfield earthquake recordings, observed particle motions are rather circular and peak velocities have relatively large values at FP and V components, even comparable to that at fault-normal (FN) component. We investigate which more realistic features can explain the controversy and thus have to be included in the modeling, namely: a non-planar fault, realistic three-dimensional (3-D) medium, the topography of the area. We test and quantify these hypotheses using the discrete wavenumber and the discontinuous Galerkin modeling methods applying 1-D and 3-D velocity structures, respectively, and two non-planar rupture models. We compare the synthetic and observed particle motions and peak velocity ratios and conclude that deviations from a planar rupture geometry in reasonable bounds for the Parkfield fault and the influence of topography only partially explain the behavior of the observed seismograms. On the contrary, the heterogeneous 3-D velocity structure significantly reduces the synthetic peak ratios to values closer to one and provide rather circular particle motions. Therefore, either non-planar rupture in 1D modeling or 3-D velocity medium are to be included in the simulations to obtain realistic estimates of ground motions at near-fault distances.

@article{id1369,
  author = {Gallovic, Frantisek and K\"aser, Martin and Burjanek, Jan and Papaioannou, Ch.},
  doi = {10.1029/2008JB006171},
  journal = {J. Geophys. Res.},
  language = {en},
  pages = {B03308},
  title = {Three-dimensional modeling of near-fault ground motions with nonplanar rupture models and topography: Case of the 2004 Parkfield earthquake},
  volume = {115},
  year = {2010},
}

%O Journal Article
%A Gallovic, Frantisek
%A Käser, Martin
%A Burjanek, Jan
%A Papaioannou, Ch.
%R 10.1029/2008JB006171
%J J. Geophys. Res.
%G en
%P B03308
%T Three-dimensional modeling of near-fault ground motions with nonplanar rupture models and topography: Case of the 2004 Parkfield earthquake
%V 115
%D 2010