MA-CME Scenarios for the 2/21/08 M6.0 Wells and the 4/25/08 M5.0 West Reno-Mogul Earthquakes

Computations by John N. Louie, August 2008 - February 2009
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These annotated videos present two scenarios for the ground shaking generated by each of two earthquakes: the April 25, 2008 magnitude 5.0 West Reno-Mogul event; and the February 21, 2008 Wells event. The four scenarios are:

1. West Reno-Mogul, basins from a regional database;
2. West Reno-Mogul, basins from a detailed local database;
3. Wells, rupture directivity toward the west;
4. Wells, rupture directivity toward the east.

To see additional earthquake scenarios affecting Nevada cities, please visit crack.seismo.unr.edu/ma .

The wave-propagation animations each last 10 seconds, and they are sped up by a factor of ten over the 100 sec of wave propagation that is simulated. The the initially coherent earthquake energy soon converts to drawn-out horizontal vibrations of energy trapped in the soft sedimentary basins that are sprinkled through Nevada like the holes in Swiss cheese- each basin rings like a gong. This trapped energy has the highest amplitude and presents the greatest shaking hazard. Though the trapped energy looks like noise, these synthetics have clean viscoelastic wave propagation with no noise or stochastic effects added.

The animations showing the wave propagation illustrate the trapping and amplification well. Each frame of the animations presents a map of 3-component ground motions for the region on the map. The West Reno-Mogul computation map was 34.8 km (21.3 mi) wide E-W and 39.8 km (24.3 mi) high N-S, with a spatial precision of 80 meters and computed shaking frequency of 1.0 Hz. The Wells computation map covers a larger area 226 km (138 mi) wide E-W and 226 km (138 mi) high N-S, with a spatial precision of 300 meters and computed shaking frequency of 0.5 Hz.

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. Where there is no color, and you can just see the gray shaded-relief of the basin model, there is very little ground motion; red is motion in the X direction (East, horizontal on the screen); green is motion in Y (North, 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).

The wave propagation movies were created with the help of the software listed on the Creating Wave-Propagation Movies page.