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by Jonathan Stewart and Andrew Liu
Stewart, Jonathan, and Andrew Liu (2000). Ground Motion Amplification as a Function of Surface Geology. SMIP2000
Seminar on Utilization of Strong-Motion Data, p. 1 - 22.
Click on the link below for the full text:
Abstract
Empirical relationships are developed to predict amplification factors for 5% damped spectral
acceleration as a function of surface geology. Amplification factors are derived for spectral
periods T = 0.01 – 5 s by assigning a reference spectrum to > 700 recordings from shallow
crustal earthquakes. The reference spectrum is derived from soft rock attenuation relations
modified to account for event-specific source/path peculiarities and rupture directivity
effects. Strong motion sites are classified according to three geologic classification schemes:
age only, age + depositional environment, and age + material gradation. Within each scheme,
amplification is regressed against ground motion amplitude, and for one scheme, against
amplitude and duration. The material gradation scheme is found to produce the least scatter
in the amplification functions. The results of the regression indicate significant nonlinear
ground response effects, and pronounced variations in the levels of amplification across
geological categories. Amplification is also found to be sensitive to the duration of strong
shaking. Due to the soft rock reference spectra used in this study, amplification levels are
smaller than had been identified in previous studies employing reference motions from relatively
firm rock sites.
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