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Analysis of Strong Ground Motions from the June 12, 2005 Anza Earthquake

by Robert Graves, Paul Somerville, Nancy Collins, Arben Pitarka and Sidao Ni

Graves, Robert, Paul Somerville, Nancy Collins, Arben Pitarka, Sidao Ni(2007). Analysis of Strong Ground Motions from the June 12, 2005 Anza Earthquake. SMIP07 Seminar on Utilization of Strong-Motion Data, p. 1 - 20.

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For shaking periods less than about 1 second, the observed ground motions from the 2005 Anza earthquake are significantly higher (around +1 sigma) than predicted by three recent NGA attenuation relations, with little systematic dependence on distance, Vs30 or Z2.5. This same trend is found comparing these data to motions computed from a broadband simulation technique. For shaking periods greater than about 1 second, both the empirical models and the numerical simulations do well at reproducing the median level of the data. We obtain a significant improvement in the fit to the shorter period motions by increasing the corner frequency in our broadband simulation by a factor of 1.6. These results suggest that the strong short period motions resulted from a rupture process having a relatively high dynamic stress drop.