ESTIMATION METHOD FOR THE SHAPE OF ENGINEERING BEDROCK USING THE VERTICAL FOURIER SPECTRUM BY MICROTREMOR OBSERVATIONS

Abstract

 Seismic ground motion can be locally amplified at the site where engineering bedrock is inclined. The amplification due to irregular ground should be taken into consideration in design ground motion. So, it is necessary to judge whether the engineering bedrock of the site is irregular. This irregularity is judged from the shape evaluated by interpolation between some soil surveys. The surface ground under railway / road structures greatly varies at each construction site and there is a possibility of overlooking the irregular ground. In this paper, we proposed estimation method of the shape of engineering bedrock using the vertical Fourier spectrum by microtremor observations. Specifically, the ratio of vertical Fourier spectrum according to the depth of engineering bedrock is estimated based on the theory of identifying the Green’s function between sites. Finally, we performed microtremor observations on irregular ground and it is confirmed that the shape of bedrock can be estimated appropriately.