Late Pleistocene Volcanic Ash Layers in Core MD972142,Offshore from Northwestern Palawan,South China Sea: A Preliminary Report

A method using the specific barrier model(Tsai,1998)is adopted hereto simulate ground motion accelerations for the purpose of seismic hazardanalysis at sites near a dominant fault system.The technique incorporatesthe simulation of fault geometry and adopts an appropriate relationshipbetween stress drop and seismic moment to estimate the number of crackson the fault for the barrier model.Radiated direct shear waves are establishedfollowing Boore's(1983)procedure.The simulated peak ground accelerations(PGA)are then calibrated by strong-motion data.Basically,the model is of uniform source,and the directivity of the source is ignored.The results show that the calibrated PGA values are neither sensitiveto the relationship between the stress drop and seismic moment and nor tothat between the fault rupture length and magnitude.However,the calibratedPGA values may increase about 20 percent for sites near the faultwhen the cut-off frequency,f(subscript max),is raised from 5Hz to 10Hz.The variabilityof the simulated ground motion is,in general,smaller than that ofthe empirical strong-motion data shown in the literature.This may be improvedby adding randomness to the parameter of f(subscript max)and uncertaintiesinto the empirical relationships adopted in the model.The calibrated attenuationcurves are used to judge which types of conventional attenuationequations are better at representing the attenuation of PGA's for sites nearthe fault,especially for large earthquake events.The results infer that,among the four attenuation equations in Tsai et al.(1987),the Joyner andBoore's form seems to be the most adequate one for ground motion estimatesin the near-source regime in Taiwan.

並列關鍵字

South China Sea ； Pleistocene ； Volcanic Ash ； Tephrochronology

國際替代計量

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