Style-of-Faulting in Ground-Motion Prediction Equations |
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| Authors: | Julian J Bommer John Douglas Fleur O Strasser |
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| Institution: | (1) Department of Civil and Environmental Engineering, Imperial College London, South Kensington Campus, London, SW7 2AZ, UK |
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| Abstract: | Equations for the prediction of response spectral ordinates invariably include magnitude, distance and site classification
as independent variables. A few equations also include style-of-faulting as a fourth variable, although this has an almost
negligible effect on the standard deviation of the equation. Nonetheless, style-of-faulting is a useful parameter to include
in ground-motion prediction equations since the rupture mechanism of future earthquakes in a particular seismic source zone
can usually be defined with some confidence. Current equations including style-of-faulting use different schemes to classify
fault ruptures into various categories, which leads to uncertainty and ambiguity regarding the nature and extent of the effect
of focal mechanism on ground motions. European equations for spectral ordinates do not currently include style-of-faulting
factors, and seismic hazard assessments in Europe often combine, in logic-tree formulations, these equations with those from
western North America that do include style-of-faulting coefficients. In this article, a simple scheme is provided to allow
style-of-faulting adjustments to be made for those equations that do not include coefficients for rupture mechanism, so that
style-of-faulting can be fully incorporated into the hazard calculations. This also considers the case of normal fault ruptures,
not modelled in any of the current Californian equations, but which are the dominant mechanism in many parts of Europe. The
scheme is validated by performing new regressions on a widely used European attenuation relationship with additional terms
for style-of-faulting.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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| Keywords: | attenuation relations fault rupture mechanism logic-tree analysis seismic hazard assessment |
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