| | AbstractA new method is
presented in this article to visualize two different sources in the
uncertainty of attenuation regression relations. The method utilizes the
residuals from regression equations, defined as the log of the ratio of
observed to predicted ground-motion parameters, from stations that have
recorded more than one earthquake. The earthquake-to-earthquake variance
is first calculated. Then the residuals are corrected with the mean
residual of the corresponding earthquake. The corrected residual from
one event is plotted versus the corrected residual from another event
for every station that has more than one record. If site effects are
perfectly represented in the regression, the resulting scatter plot will
show statistically uncorrelated points, while extension along the
diagonal and a positive correlation coefficient is the result of a
contribution from site effects. This simple strategy allows us to
visualize the uncertainty caused by the earthquake source and path in
regression relations and indicates quantitatively how much we can
improve the prediction by adding additional site information. The
results obtained from this method are very similar to those that are
calculated directly from the method proposed by Joyner (personal comm.,
1997). In southern California, we find that source and path effects
dominate the uncertainties at high frequency, while at low frequency,
the regression can be still improved more significantly by correcting
for the site effects.Return to
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