HR: 0800h
AN: S41A-0947    [Abstracts]
TI: Finite Element Modeling of Dynamic Shear Rupture Experiments Along Non-Planar Faults
AU: * Templeton, E L
EM: templet@fas.harvard.edu
AF: Division of Engineering and Applied Sciences, Harvard University, 29 Oxford St., Cambridge, MA 02138 United States
AU: Baudet, A
EM: abaudet@esag.deas.harvard.edu
AF: Departement de Mecanique, Institut des Sciences et Techniques de l'Ingenieur, Lyon, 69125 France
AU: Bhat, H S
EM: bhat@esag.deas.harvard.edu
AF: Division of Engineering and Applied Sciences, Harvard University, 29 Oxford St., Cambridge, MA 02138 United States
AU: Rice, J R
EM: rice@esag.deas.harvard.edu
AF: Division of Engineering and Applied Sciences, Harvard University, 29 Oxford St., Cambridge, MA 02138 United States
AU: Rice, J R
EM: rice@esag.deas.harvard.edu
AF: Department of Earth and Planetary Sciences, Harvard University, 20 Oxford St., Cambridge, MA 02138 United States
AB: The study of dynamically propagating shear cracks along weak paths like faults is of great interest for the study of earthquakes. We adapted the ABAQUS/Explicit dynamic finite element program to analyze the nucleation and propagation of shear cracks along a non-planar, kinked, weak path corresponding to the one that was used in recent laboratory fracture studies by Rousseau and Rosakis [{\it JGR}, 2003]. Their experiments involved impact loading of thin plates of Homalite-100, a photoelastically sensitive brittle polymer, which had been cut along a kinked path and then weakly glued back together everywhere except along a starter notch near the impact site. Under different conditions, propagation speeds were observed in both the sub-Rayleigh and intersonic (supershear) regimes. Strain gage recordings and high speed photography of isochromatic lines (lines of constant difference between the in-plane principal strains) provided characterization of the transient deformation fields associated with the impact and fracture propagation. For the finite element analyses, we implemented a slip-weakening failure model through an option in the ABAQUS program allowing user defined constitutive relations. The analyses of impact loading and of rupture nucleation and propagation were then carried out in the 2D framework of plane stress. In a first set of studies of nucleation and propagation of rupture along a straight fault, we determined after some trial and error an appropriate CFL number, and examined different element types and layouts, finding that the most acceptable results were obtained for low order elements. We used constant strain triangles, arrayed in groups of four to effectively form four-sided elements with corner nodes and one internal node. The studies also showed that to obtain representations of slip rate and shear stress near the propagating rupture tip that were relatively free from numerical oscillations, it was necessary to have element side lengths of order $R_o/50$, where $R_o$ is the estimated slip weakening zone size under quasistatic conditions. We then turned to analyses that explicitly represented the impact loading (as an imposed motion at the contact boundary) and kinked weak path of the experiments. We found that depending on parameter range we could, as in the experiments, produce either sub-Rayleigh or intersonic propagation speeds, and that rupture followed the kinked path. Also, while not obtaining extremely close agreement with the high-speed experimental measurements, we found that we could produce the principal features observed in the dynamic isochromatic line patterns and strain gage recordings.
UR: http://esag.harvard.edu/rice/BaudetTemplBhatRice\_30Aug04.pdf
DE: 7260 Theory and modeling
DE: 8123 Dynamics, seismotectonics
DE: 7209 Earthquake dynamics and mechanics
DE: 3210 Modeling
DE: 3230 Numerical solutions
SC: Seismology [S]
MN: 2004 AGU Fall Meeting