札幌都市域における深部地下構造調査と強震動観測

概要

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Sapporo urban districts are located on a deep sedimentary basin in the western part of the Ishikari depression, Hokkaido. It is important for evaluation of the seismic response of Sapporo urban districts to know the deep subsurface structures. We have summarized various data relating to the subsurface structures ; a few deep boring data to a depth of about 4000 m and several PS-logging data to a depth of about 500 m. We have estimated S-wave velocity structures under the northern part of Sapporo urban districts by using the microtremor exploration method. The basement layer has an S-wave velocity of about 3000 m/s at a depth of about 3000 m. We have carried out strong motion observations at 15 sites in Sapporo urban districts in order to evaluate directly the seismic response. Here we show a preliminary result of the spatial variation of site amplifications in the districts using strong motion records from an intermediate-depth earthquake. We evaluate the spatial variation of site amplifications as a function of periods based on band-pass filtered records with various pass-bands. At the northern part, long-period seismic waves with a period of about 5 sec are strongly amplified, while at the central part, short-period seismic waves with a period of about 1 sec are strongly amplified. Finally we have examined the effect of the estimated deep subsurface structure on seismic motion based on observed S-waves.
日本自然災害学会の論文
2001-11-30