Preliminary Study On Ground Motion Attenuation Relationship For Western China

Ground motion attenuation relationship is the key part of seismic hazardanalysis and important basis of determining the design ground motion. Theobjective of ground motion attenuation relationship research is to develop areasonable model to describe the characteristics of ground motion and predictground motion more accurately with less uncertainty. The numerous recordsfrom large earthquakes in recent decades demonstrate lots of new specialcharacteristics, such as hanging wall/footwall effect, rupture directivity effect.Therefore, it’s significant to develop an updated attenuation relationship as anew reference for the seismic hazard analysis in China. The new attenuationrelationship should include more factors affecting ground motion and simulatethose new characteristics.In this thesis, a comprehensive ground motion model considering theeffect of rupture mechanism of source and site condition and reflecting thesaturation of ground motion and near field effects is presented. Some key pointsin attenuation relationship are discussed. The main work and conclusionsinclude：1. Applicability of NGA models to Wenchuan earthquake were discussedfollowing the comparison of five NGA models. The results indicate that, NGAmodels under-predicted ground motion produced by Wenchuan earthquake atshort periods for T<0.5sec, but over-predicted it at long periods for T>1sec.2. Source information of Wenchuan earthquake and its aftershocks and sitecondition of observing stations were collected and collated. A method ofestimating the geometrical features of rupture for small and moderateearthquake was presented. This method was used to get the Fault Parallel (FP)and Fault Normal (FN) components of ground motion and to estimate therupture distance for Wenchuan aftershocks.3. A functional form with segmented magnitude scaling was established asbased model. Period depended subsection point of magnitude was adopted toavoid the subjectivity of commonly-used constant subsection point ofmagnitude. A site effect factor as a function of Vs30instead of the broad andambiguous site categories，was developed to consider the difference in the samecategory. In this thesis, concise models for hanging wall/footwall effect andrupture directivity were developed by residual analysis. 4. Random effect regression was used to determine the coefficients in themodel. Comparison between this model and NGA models show that, medianground motion at short periods predicted by this model is consistent with NGA,but smaller than NGA predicted value at long period; the standard deviation ofthis model is slightly lower than NGA models, but larger than AS08and CY08models.