Study On Ground Motion Amplification Of Regional Site And Application

The shear wave velocity from surface to30meters depth (Vs30) was used assite classification index in internation. However, measurement of Vs30wasdependent on drilling, which was obviously unpractical for large area. Thereforethe method of calculating Vs30was put forward. The spectral ratio method ofsurface rock reference site is dopted in estimation of site amplification effect forsoil layer generally, so how to select the surface rock reference site and whichstandard should be used had became significant problems. For the surface anddown hole strong motion observation array, there are some problems still existedin the down hole rock reference site spectral ratio. At present, the Chinese seismiccode did not consider the obvious difference among the ground motions ofdifferent site condition. Although the shape of design response spectra wasmodified, the platform value was not changed. So it is a key problem on how toobtain site amplification coefficient based on the Chinese site classification. Inrecent years, with the increasing of digital strong motion records of greatearthquakes in China, it became significant to study the site effect on long periodstrong ground motion and the effect of long period strong ground motion on thereliability of Chinese design response spectra in the long period phase. Thedevelopment of technical mean of earthquake disaster loss evaluation system wasrelatively backward at present and the ability of integrating seismic data inearthquake field was limited, so the development of new earthquake disaster lossevaluation system should be further studied. This paper centered on such issues asthe topic of the thesis, major contents are abstracted as following:1. Study on estimation of regional site Vs30and PGA amplificationcoefficientEstimation of Vs30method was put forward based on geology andtopographic slope, and the Vs30distribution map of Guangdong Province wasdrawn by this method. The site Vs30correction method was also proposed basedon engineering borehole data and site Vs30correction of Guangdong and Sichuanprovince was realized. In the case of statistic analysis relationship of Vs30andpeak acceleration amplification coefficient, PGA distribution map of Wenchuanwas drawn. It showed that the estimation of Vs30method and the correlationmethod improved estimation accuracy of regional Vs30, which had wideapplication in the intensity quick report system, seismic design,ground motionattenuation relationships and seismic zoning.2. Standard reference site selection and depth correction modelBased on the study of rock site amplification effect, the limitations of Vs30standard for rock reference site selection in Europe and the United States wasanalysed, The double standard Vs30and predominant frequency f0was promotedto select rock reference site, whose rationality was also verified. In order toovercome the defect of the down hole rock reference site spectral ratio for surfaceand down hole strong motion observation array, based on the analysis of thedrilling depth impact, a depth correction model of down hole rock reference sitespectral ratio was put forward. By analyzing the rationality of the model, it could come to a conclusion that depth correction model was very reliable.3. Study on site amplification of Chinese site classificationIn order to get the site amplification coefficient of short-period Fa andmedium-period Fv, strong motion records and borehole data were collected fromJapanese KiK-net strong ground motion arrays, and then according to thestandard Chinese site classification, the stations site classification were completed.With the down hole rock reference site spectral ratio, depth correlation andgeometric mean, the average spectra of every station site was calculated. Takingaverage value within the range period0.1~0.5s and0.5~2.0s, standardizing on thebasis of I site classification, in the end site amplification coefficient ofshort-period Fa and medium-period Fv were gotten. Through comparativeanalysis, the rationality of short-period Fa and medium-period Fv were verified.The achievement is very effective to adjust the value of Chinese design responsespectra platform.4. Characteristic analysis of site amplification for thick overburdenBased on the Wenchuan main shock and after shock records, the PGA andresponse spectra value at period0.1s,5.0s,10.0s of27stations in Weihe basinwere calculated.With the spatial interpolation method, the spatial variationcharacteristics of PGA and response spectra value were analized. The resultsshowed that the quaternary overburden thickness controlled action on long-periodstrong ground motion. For further study of long-period ground motioncharacteristics, comparative analysis of variation regulation of accelerationresponse spectra with site, magnitude and distance factors was done, and then theresponse spectra of class C+D site in Wenchuan earthquake and the Chineseseismic code response spectra of class II site were compared, it could beconcluded that Chinese seismic code response spectra applying to seismic designof long-period structure was not reliable. Our research on seismic wave selectionand reliability of long-period seismic design has a certain significance.5. Study on ground motion rapid generation systemThe development status of strong motion observation technology issumarized, in the quasi-real-time intensity quick report system rapid assessmentmethods of faults, meizoseismal area and Macro epicenter were put forward.