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PAGE, M.T., DUNHAM E.M., and CARLSON, J.M., University of Califonia, Santa Barbara, CA 93117,,,

We present dynamic modeling of the 1984 Morgan Hill earthquake. We choose this earthquake due to large, late pulses in several of the observed seismograms. These make Morgan Hill a candidate for the energy-focusing mechanism found by Dunham et al. [2003], in which high-strength barriers concentrate energy to produce strong ground motion. We believe that such a barrier, loaded close to failure, is responsible for the large-amplitude pulses in the Morgan Hill earthquake. The kinematic inversion of Beroza and Spudich [1988] finds that the large late pulses in the displacement records are caused by a localized region of high slip far from the hypocenter. Starting with the slip distribution and rupture history given by Beroza and Spudich, we first simulate the rupture kinematically with an eighth-order finite-difference method. We use the stress history from the kinematic model to determine the yield stress and prestress along the fault. We then use these stresses as input in the dynamic modeling. This is done using a 3-D finite-difference method with slip-weakening friction. Our kinematic inversions suggest that the large late pulses shown in the observed seismograms are caused by a region that is both an asperity and a barrier. We hope to obtain an improved fit to the large-amplitude pulses with a dynamic model that has heterogeneities in both prestress and yield stress.


Last Modified: 2011 Aug 10