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[SSS10-P10] Basic study of ground amplification factor based on microtremor array observations at seismic stations in the Kanto region.
Keywords:Underground structure model, Microtremors, Strong Ground Motion Prediction, S-wave velocity
At the NIED, we have constructed a shallow and deep integrated ground structure model in the Kanto region for the purpose of evaluating strong ground motion over a wide band, and the AVS30 and ground amplification factor (maximum velocity amplification factor) based on the constructed ground model are released by the HERP and J-SHIS on March 26, 2021. In creating this model, an initial model was created with about 310,000 boring data in the entire Kanto region, and based on the analysis results of about 14,000 points at intervals of about 1km (3rd mesh unit) based on lowlands and plateaus. A underground strucuture model with 250m mesh intervals has been constructed and the ground amplification factor has been evaluated. At some seismic stations, microtremor array observations are also carried out, and the amplification characteristics for each period are verified by seismic response calculation based on the seismic observation record and the S-wave velocity structure of the microtremor array (HERP (2017, 2021)). As a result, it has been confirmed that the accuracy of the S-wave velocity structure based on the microtremor array observation is very high. The evaluation of the ground amplification factor by the current surface ground model was carried out by Fujimoto and Midorikawa (2006), but the AVS30 used for the ground amplification factor is based on the PS logging of K-NET and KiK-net.
In this study, as part of the accuracy verification of the ground amplification factor by AVS30 using the underground model, the relationship between AVS30 and the ground amplification factor based on the S wave velocity structure obtained from the microtremor array was evaluated.
In the future, the purpose is to be able to evaluate the optimum ground amplification factor if microtremor array observation is carried out.
First of all, all observation points (225 points) excluding K-NET and KiK-net sea areas and remote islands in the Kanto region including Yamanashi prefecture, local government seismographs (130 points mainly in Chiba and Ibaraki prefectures), MeSO-net (293 points) Small array exploration with a radius of 10m or less and a radius of 60cm was carried out at Just Point of seismic station, a total of 648 observation points. Good results that can be evaluated by AVS30 can be obtained at all the observed points. The calculation of AVS30 is based on the method based on the wavelength 40m (C40) based on Nagao and Konno (2002), the S-wave velocity structure based on the 1/3 wavelength rule, and the phase based on the method of Arai and Tokimatsu (2004, 2005). The S-wave velocity structure based on velocity and inversion analysis by H / V was examined respectively.
In this study, as part of the accuracy verification of the ground amplification factor by AVS30 using the underground model, the relationship between AVS30 and the ground amplification factor based on the S wave velocity structure obtained from the microtremor array was evaluated.
In the future, the purpose is to be able to evaluate the optimum ground amplification factor if microtremor array observation is carried out.
First of all, all observation points (225 points) excluding K-NET and KiK-net sea areas and remote islands in the Kanto region including Yamanashi prefecture, local government seismographs (130 points mainly in Chiba and Ibaraki prefectures), MeSO-net (293 points) Small array exploration with a radius of 10m or less and a radius of 60cm was carried out at Just Point of seismic station, a total of 648 observation points. Good results that can be evaluated by AVS30 can be obtained at all the observed points. The calculation of AVS30 is based on the method based on the wavelength 40m (C40) based on Nagao and Konno (2002), the S-wave velocity structure based on the 1/3 wavelength rule, and the phase based on the method of Arai and Tokimatsu (2004, 2005). The S-wave velocity structure based on velocity and inversion analysis by H / V was examined respectively.