3-D Earthquake Movies
Results from this research project are being presented at the 92nd Annual Meeting of the Seismological Society of America
The movies show snapshots of S-wave propagation from simulations of moderate Bay Area earthquakes through a model of three dimensional structure. This is achieved using a numerical finite difference method on a grid of points extending 175 km x 100 km x 40 km in dimension. The extent of the grid is shown as the red rectangle. These simulations use nearly 2 Gbytes of memory and require 10 hours of computation time on a supercomputer. In all of the frames, the cool colors represent negative amplitudes and the warm colors positive amplitudes, and the brightness of the color increases with amplitude. White and violet are the largest amplitudes. The frames show snapshots of the wave patterns every 3 sec in real time, for a total duration of 90 sec.
Warning! These movies may not be rendered correctly by a monochrome monitor.
Movie 1 is a simulation of a magnitude 4.8 earthquake which occurred on the Calaveras fault east of San Jose on May 21, 1996. As the waves spread out from the source, several interesting patterns can be observed. In the first few frames low amplitude energy advancing ahead of the main wave front is caused by P-wave energy converted to S-waves at the edge of the Santa Clara Valley. The main wave front is visibly refracted or bent by contrasts in the velocity across both the Hayward and San Andreas faults. The effect is similar to what happens when you view an object which is underwater. See the map of Bay Area faults on the Seismographic Station page for the locations of these faults. Concentrations of high amplitude standing waves persist throughout the movie around San Jose and in San Pablo Bay. These areas are low-velocity sedimentary basins and cause the amplitudes of ground motion to be amplified as well as extend the duration of the motions. Both of these factors increase the level of hazard to structures. These basins also radiate scattered waves into surrounding areas, which can be seen quite clearly in these movies. If you look closely enough, you can also see waves bent around the edges of these basins as they pass by.
Movie 2 is a simulation of a magnitude 4.2 earthquake which occurred near Berkeley on June 26, 1994. The wave amplitudes will thus be smaller throughout than in Movie 1. Many of the same features can be seen here as in Movie 1, although the precise patterns will be different due to the differing source location. By comparing these frames with those in Movie 1, it is possible to see how the amplitude and duration of ground motions at a specific site will be different due to earthquakes occurring at different locations.
We are also simulating ground motions due to hypothetical large earthquakes that might occur on the Hayward fault. This page contains movies and other information for various M7 scenarios. Note how the directivity effect amplifies motions in the direction of the propagating ruptures.
This work is supported by the National Earthquake Hazard Reduction Program, the Livermore Advanced Computer Initiative in Science and Engineering, and the Campus-Laboratory Collaboration program. For additional information, please contact: