Vertical amplification of superficial soils during earthquakes

Abstract

The downhole array data recorded at Port Island, Kobe, during the 1995 Hyogoken-Nanbu Earthquake are of particular interest in earthquake geotechnical engineering. Fig. 1 depicts the distribution of peak accelerations along the depth in three components. It is noticed that although both horizontal motions were de-amplified due to soil liquefaction in superficial layers, a remarkable amplification of vertical motion was observed. While a number of studies have been devoted to the effects of soil liquefaction on horizontal motion, the significant vertical amplification has received little attention. However, to investigate the significant vertical amplification is of interest not only from the viewpoint of interpretation of this site-specific phenomenon, but also in applications in site evaluation using a technique known as H/V, which involves analysis of the spectral ratio of horizontal to vertical components of microtremor. Therefore, a study has recently been conducted to analyze this problem and a part of the work is reported herein.