Synthesis of regional ground motion from western US earthquakes. Final report Nov 1977-Dec 1978

Synthetic displacement, velocity and acceleration seismograms and the resulting response spectra are computed and analyzed for earthquake ground motions in the western United States. A source model for the 1975 Pocatello Valley earthquake is used with plane layered earth models to estimate the ground motions at Minuteman Wing V which is at a range of about 700 km. The 1975 Yellowstone earthquake was a similar event at the same range from Wing V. However, the ground motions are estimated to be an order to magnitude smaller due to three effects: the two earthquakes were the same size at long periods but the Yellowstone event appears to be a factor of 2 to 4 smaller at short periods; the sources are oriented such that radiation pattern differences between the two events are nearly maximum; the Yellowstone caldera and, perhaps, other highly attenuating structures to the south cause the Wing V ground motions from the Yellowstone event to be much smaller than otherwise expected.