1. Analyis of Bridge Structures Crossing Fault Rupture Zones: Seismic Ground Motion Simulation
Douglas Dreger, Gabriel Hurtado, and Anil Chopra
University of California, Berkeley

2. Objective
Develop a set of characteristic near-fault (10s of meters distance) ground motions for engineering design.
Explore ground motion sensitivity to faulting style and rupture behavior.
In particular consider cases with surface rupture where ground motions have both dynamic and static components.

3. Elastic Dislocation of a Mw6.5 Earthquake

4. Computational Method 4th order staggered grid finite-differences
Complete wavefield computation
Arbitrary model complexity
Velocity Structure
Half-space, layered (1D)
Source Complexity
Uniform slip
Variable slip, rise time and rupture velocity
Computational requirements
Grid spacing (20m), fmax (20 Hz), model size (2.3 Gp), requiring 119 Gbytes of memory
Computations are performed on the LLNL MCR supercomputer using 512 processors

5. Finite-Difference Grid and Station Subarray PositionFP FN

6. Considered Fault Geometries

7. Source Characteristics
Mw 6.5
28.8km x 9.3km length by width fault from Wells and Coppersmith (1994)
0.71m of uniform slip
variety of faulting style (strike-slip to thrust)
constant 0.5 second rise time from Somerville et al. (1999)
sensitivity to rise time is examined
constant rupture velocity of 80% of the shear wave velocity
sensitivity to rupture velocity is examined

8. Comparison of Displacement Results
Strike-slip
Oblique
Reverse
Thrust

9. Comparison of Velocity Results
Strike-slip
Oblique
Reverse
Thrust

10. Strike-Slip Results
Fling
Controlled

11. Strike-Slip Results
Fling
Controlled
Directivity
Controlled

12. Are The Peak Ground Velocities Reasonable?

13. Dip-Slip Results
Strike-Slip Case
Dip=40; rake=110 case

14. Z component Displacement Motions Away from Fault

15. Rise Time Sensitivity - FP Component

16. Rise Time Sensitivity - FN Component
rt=0.3s
rt=0.5s
rt=0.7s

17. Variable Slip Models Kinematic Model
Method of Mai and Beroza (2001) to obtain random slip distributions
Assume constant rupture velocity
Assume constant slip velocity - leads to variable rise time
Models have variable variable static offset close to the fault, and degrees of rupture directivity
Cumulative Slip

18. Conclusions