长周期地面脉动在地震小区划中的应用

The Application of Long Period Microtremor to Seismic Microzonation

应用长周期地面脉动测定场地放大因子，作为地震动小区划的一种手段，近年来在国内外有了很快发展．但至今仍有很多基本理论问题尚未得到澄清，如长周期地面脉动究竟由哪种波所制约，它与产生强震地面运动的地震波有无可比性；非线性效应对长周期部分有多大影响等．本文在广泛总结国内外资料基础上，结合与日本京都大学防灾研究所的合作研究和上海地震小区划的实际，回答了以上问题．着重讨论了土壤场地相对于基岩场地的傅氏谱比值在周期大于１ｓ情况下。作为一阶近似可以忽略非线性影响，从而为长周期地面脉动应用于地震动小区划提供了可能性．

There has been a rapid develpment in measuring the magnification factor of a site by means of long-period microtremor in recent years. But there are still many basic theoretical problems in need of being clarified now. For instance, there are questions of by what kind of wave the long-period microtremor is actually monitored, whether it can be compared with strong seismic ground motion, how much influence there is on long-period part caused by nonlinear effect, and so on. These questions are answered in this paper on the basis of summarizing the achievements obtained in China and abroad, the joint-research between DPRI, Kyoto University, Japan and Shanghai institute for Disaster Prevention and Relief, and our experience of Shanghai seismic microzonation. The authors put the focus on the problem of fact that nonlinear effect on the Fourier spectral ratio (soil site/rock site) in the range of period greater than 1 secondcould be neglected under 1st order approximation. This provides a possibility to apply long-period microtremor measurements to the seismic microzonation.