Final Project Summary— PEER Lifelines Program
Project Title—ID Number
Start/End Dates
Project Leader (boldface) and
Other Team Members

Validation of Basin Response Codes—1A01
Budget/9/1/99 – 9/30/00
Funding Source$100,000 / PG&E

Henyey/Day (SCEC/SDSU)

1. Project goals and objectives

Numerical simulations of wave propagation can now be done in three dimensions for models with
sufficient realism (e.g., three-dimensional geology, propagating sources, frequencies approaching 1 Hz)
to be of engineering interest. However, before numerical simulations can be applied in the context ofengineering studies or seismic hazard analysis, the numerical methods and the models associated withthem must be thoroughly validated. Task 1A01 focused on validation of the underlying numericalmethodologies and computer programs employed in numerical modeling of earthquake ground motion
from propagating earthquakes in 3D earth models. The emphasis in 1A01 was on idealized sources in
simple earth structures. Code verification was carried out through a systematic, coordinated program oftest simulations.
2. Benefits of the results of this project to develop technologies and protocols to mitigate the vulnerabilityof electric systems and other lifelines to damage directly and indirectly caused by earthquakes. Also,
benefits to develop assessment techniques to evaluate damage to electric systems caused byearthquakes and to assess fiscal impacts due to the loss of electric service to the community.

The project provided an essential foundation for simulation-based ground motion estimation in urban
sedimentary basins.
3. Brief description of the accomplishments of the project

Tests verified the accuracy of basic equation solvers, source formulations and free surface boundary
conditions, through comparisons with analytic solutions for uniform elastic halfspace problem. Further
tests verified the accuracy and limitations of absorbing boundary conditions used to simulate radiation
conditions at grid boundaries. Additional tests verified accuracy of material interface representation
through comparisons with analytic solutions for layered a halfspace problem. Finally, test simulations
were done to verify code accuracy for propagating earthquake sources. Test problems were documented
and made available to any interested investigators.
4. Describe any instances where you are aware that your results have been used in industry

5. Methodology employed

Five different earthquake ground-motion simulation codes were tested. Of these, four are finite
difference (FD), and one is finite element (FE). All of the FD codes use uniform, structured grids, withstaggered locations of the velocity and stress components and fourth-order accurate spatial differencingof the elastodynamic equations. The codes were independently programmed. The main variations
among them include: degree of computational parallelism, type of memory management (e.g., mainmemory contained operation versus roll-in/roll-out from disk), free-surface boundary condition
formulation, absorbing boundary formulation, material interface representation (e.g., type of averaging
of material properties in vicinity of properties gradients or interface), and source formulation.
6. Other related work conducted within and/or outside PEER
The PI and several of the co-PIs conducted related SCEC research, including developmental work on the codes that were thesubjects of this validation study.

7. Recommendations for the future work: what do you think should be done next?
(1) Testing of the methods for earth structure models with realistic levels of complexity, such as the SCEC Community
Velocity Model, and for earthquake models with realistic levels of complexity, such as the published kinematic models of the1994 Northridge, California, Earthquake. (2) Application of the methods to estimate basin amplification effects on seismic
ground motion.
8. Author(s), Title, and Date for the final report for this project
Authors: S. M. Day, J. Bielak, D. Dreger, S. Larsen, R. Graves, A. Pitarka, and K. B. Olsen

Title: Tests of 3D Elastodynamic CodesDate: September 10, 2001
9. Figures

Figure 1. Comparison of results from 4 FD and FE wave
propagation codes, at beginning (above) and end (below)of the validation study 1A01. Solutions are for uniform
halfspace. Semi-analytic solution by integral tranform
methods (“reflectivity”) is also shown, for reference.

Figure 2. Comparison of FD and semi-analyticsolutions for layer-over-halfspace test (point
dislocation source), demonstrating accuracy of FD
code.