Video

The Collaboratory for Computational Geosciences (www.seismo.unr.edu/ccog) is modeling synthetic earthquake motions through complex geological structures. The synthetic seismograms put us a few steps closer toward being able to accurately anticipate the ground shaking and other effects of likely earthquakes. The videos presented here are predictions of ground shaking for seismic recording stations in southern Nevada, many in the Las Vegas urban area. The initially sharp and coherent earthquake energy soon converts to drawn-out horizontal vibrations of energy trapped in the soft sedimentary basins that are sprinkled through this region like the holes in Swiss cheese. This trapped energy has the highest amplitude and presents the greatest shaking hazard to Las Vegas. Though the trapped energy looks like noise, these synthetics have clean linear wave propagation with no noise or stochastic effects added. The movies showing the wave propagation illustrate the trapping and amplification well. As in the graphic on the right, each frame of the movies present a map of 3-component ground motions for the tilted region on the map. The movie frames are 300 km wide from NW to SE and 200 km high from SW to NE. The movies proceed at two and a half times the real modeled time. The three primary computer display colors of red, green, and blue (RGB) are used to represent the three directional components of ground vibration X, Y, and Z, respectively. Each color is given an intensity related to the intensity of shaking motion in the respective direction. A black color indicates very little ground motion; red is motion in the X direction (horizontal on the screen); green is motion in Y (vertical on the screen); and blue is motion in Z (in and out of the screen). Where shaking directions combine, the colors combine according to the rules of colored light- yellow indicates combined horizontal motion (relative to the ground) of X and Y, adding red and green light, so could be north-south or east-west. White color, adding red, green, and blue all together, indicates high-intensity shaking on all components, including up and down. With these colors, P waves will be mostly blue, S waves red, green, or yellow; and the Rayleigh surface wave is identifiable by having blue up-down motion between the red, green, or yellow radial motions (elliptical particle motions). We present two different models here, to explore the role of all the various basins in the region. The first model has all the basins known from geological and geophysical studies. The second model only has the Las Vegas basin. Certainly you can see a substantial difference between the models for the stations not in Las Vegas. But our research question is whether there are important differences between the predictions of these models within the Las Vegas basin.