Abstract
In this study, the predominant periods estimated from microtremor observations were compared the natural periods of surface soil layer based on boring date at 72 sites widely distributed in Miyazaki plain. The predominant periods of the microtremors H/V spectral ratio and the depth of engineering bedrock were investigated quantitatively. In addition, the relationship between the predominant periods and the S-wave velocity of surface soil layer estimated from the N-value was elucidated in Miyazaki plain. As a result, the measurement method of the natural period calculated from the law of quarter wave length has obtained reliability. A new equation has been developed to estimate the depth to engineering bedrock, based on the relationship of the predominant periods and the depth of engineering bedrock and the S-wave velocity of surface soil layer. The applicability of the proposed equation to other areas requires further research.
