Estimation On Site Characteristic Based On H/V Spectral Ratio Method

A lot of seismic damages and theoretical studies indicate that the local site conditionshave a significant impact on ground motion characteristics. Different site conditions mayinduce varied amplification of the ground motion, which is the direct reason for abnormaldamage phenomenon. With the accumulation of strong-motion records in many countries,many researchers began to study the site effect based on the strong-motion records. Manystations were triggered by the Lushan earthquake, and a large number of aftershock recordsprovide us a valuable opportunity to study site characteristics. Currently, the stong-motionrecords of China are only classified as “bedrock” or “soil”, which is difficult to meet researchneed. Therefore, It’s a meaningful work to classify Chinese strong-motion sations based onChinese seismic code. This paper is divided into three parts:1. This paper estimated the site effect of41near-field stations using the improvedhorizontal-to-vertical (H/V) spectral ratio method, and gave the preliminary sitesclassification based on the shape of spectral ratio and natural period of the sites. It proves thatthe result properly reflect the characteristic of site corresponding to the borehole profile oftypical strong-motion stations and the topography of Lushan area. Compared with thetraditional site classification in Chinese code, the H/V spectral ratio method is more suitableand stable to reflect the seismic response.2. This paper analyzed the nonlinear site effect by comparing the difference of H/Vspectral ratio between the weaker aftershocks (<30gal) and stonger mainshocks(>100gal). Weobserve the shift of predominant frequency of H/V curves except for some rock or firm soilsite. The fNL(a frequency from which we observe deamplification beteen nonlinear and linearsite response)and the DNL(degree of nonlinearity site response) were calculated formentioned stations. We also find a good correlation between the DNL and the nomalizedshear wave velocity.3. We proposed a promising site classification scheme based on strong-motion data fromJapanese KiK-net stations, and calculated the mean site classification curves using the H/Vspectral ratio method based on Chinese code from294stations of KiK-net. An empiricalmethod for Chinese site classification was proposed according to the range of predominantperiods, peak value of H/V spectral ratio and the spectral shape. Compared with the boreholeinformation of stations in Sichuan Province, the classified result is independent of thedifferent regions. Using this method, we were able to classify Chinese113strong motionstations based on the records obtained from2007to2011. The suggested site classifications 4. provides valuable information for use of strong-motion records.