Annual Meeting - SCEC.org

Poster Abstracts | Group 1 – ExGM
energy partitioning during rupture, and find that the plastic strain energy dissipated in the bulk
can be several times the slip-weakening fracture energy.
1-069
SPATIAL CORRELATION BETWEEN KINEMATIC SOURCE PARAMETERS
DERIVED FROM DYNAMIC RUPTURE SIMULATIONS Schmedes J, Archuleta RJ, and
Lavallee D
For a kinematic model to accurately predict ground motion, it is necessary not only to know the
spatial distribution of the source parameters but also to know the correlation among the
parameters. Because there are limitations from inversions of seismic data, we determine the spatial
correlations from physically based dynamic ruptures.
We computed and analyzed 150 dynamic subshear rupture models to get a quantitative
understanding of the correlation and amplitude distributions of parameters describing the
earthquake source, such as stress drop, rupture velocity, and rise time. The dynamic ruptures are
based on a slip weakening friction law and different approaches to create random heterogeneous
initial stress and strength distributions on the fault. While there is much to be learned by looking at
differences among all the models, we focus on features that are common among all models, that is,
features that show the least dependence on the choice of the initial model. Using the 150 dynamic
ruptures, we are able to construct probability density functions (PDF’s) for the amplitude
distributions of the source parameters as well as for the spatial correlation between the source
parameters.
We find: (1) slip amplitude does not show systematic correlations with rupture velocity, and it is
positively correlated with rise time; (2) peak slip rate shows strong correlation with rupture
velocity and rise time; (3) the PDF of rupture velocity has a well defined maximum between 80%-
90% of the shear wave velocity. The value of this maximum probability density increases with
distance from the hypocenter, while the width of the PDF decreases, i.e., the rupture velocity tends
toward a more constant value. A similar dependence is found for the PDF of the rise times, which
has a width that decreases with increasing distance from the nucleation zone; moreover, the mean
value of the rise time shifts to a smaller value.
Our findings will be used to refine the rupture model currently used in the SCEC broadband
simulation platform.
1-070
IS TIME/SLIP/VELOCITY WEAKENING NECESSARY IN DYNAMIC RUPTURE
SIMULATIONS? APPLICATION OF A DISCRETE ELEMENT METHOD TO MODEL
YUCCA MOUNTAIN GROUND MOTIONS Purvance MD
Using geotechnical and fault offset data, Andrews et al. (2008 - AEA08) developed dynamic
rupture models to constrain the physical limits on ground motions at Yucca Mountain. The AEA08
model uses a traction-at-split-node finite difference and includes realistic material properties,
topography, and initial stresses. To independently verify the AEA08 ground motions, this work
builds a distinct element (DEM) dynamic rupture model for Yucca Mountain. The bulk material is
discretized by a triangular lattice consisting of linear springs connecting nodes (32 m spacing, 0.25
Poisson ratio). This Lagrangian approach tracks nodal positions and velocities using the Velocity
Verlet algorithm (accurate to 4th order in position, 2nd order in velocity). The fault sides interact
through a soft contact law where normal stresses develop from overlap between a node on one side
of the fault and the opposite fault member. Shear stress increments are obtained by calculating the
106 | Southern California Earthquake Center