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Weak-Motion Test

During 1989-1990, a “Blind” Weak-Motion Test was conducted at the Turkey Flat, USA Site Effects Test Area as part of the long-term experiment plan.  For 18 months prior to the weak-motion test, the California Geological Survey teamed with the Lawrence Livermore National Laboratory to record weak ground motions across the Turkey Flat array. Weak-motion sensors were co-located at each of the strong-motion recording sites, and provided the data necessary to conduct the blind test.  The purpose of the weak-motion test was threefold, to provide:

  • A means of setting up and testing prediction models and procedures for readiness when a strong-motion event occurs;

  • An opportunity to compare very low strain ground motion predictions and observations with those at high levels of strain; and,

  • A means of validating how well dynamic soil characteristics have been estimated throughout the test site.

Principal findings from the weak-motion test are:

  • All predictions tend to group, and are successful in that the observed ground motions fall within the range of prediction uncertainties. The uncertainty, however, is large;

  • Damping in the “standard” geotechnical model may be too low, suggesting the accuracy of the site characterization is more important than the method used to calculate response; and,

  • There was a tendency to underestimate uncertainty of predictions.

Details of the weak-motion test results may be of value in the strong-motion test, and are available in the following publications:

(Cramer, 1995)

(Field and Jacob, 1993)

(Turkey Flat Report 6, 1991)

(Turkey Flat Report 5, 1990)




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