Journal of Geography (Chigaku Zasshi)
Online ISSN : 1884-0884
Print ISSN : 0022-135X
ISSN-L : 0022-135X
The Path Effects of Seismic Waves in a Sediment as Inferred from the Deep-Borehole Observation
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1988 Volume 97 Issue 5 Pages 464-475


The National Research Center for Disaster Prevention has deployed some strong-motion observation arrays in the Kanto district, in order to investigate the characteristics of seismic motions modulated by a sediment. Especially, we investigated the earthquake responses of the sediment with a thickness of several kilometers by means of down-hole arrays whose maximum depths are 600 meters or more below the top of the pre-Tertary basement.
As observational results, we made sure two fundamental earthquake responses of the sediment-basement system. One is due to the multiple reflections of S-waves at the sediment-basement system. The sediment is treated as a horizontally layered structure. The other is due to a series of total reflections of S-waves both at the surface and at the upper boundary of dipping basement. The train of totally reflected SH pulses generates a pseudo-Love wave.
More recently, we tried to separate the source spectrum, the path effect and the site amplification by using both the deep-borehole data and the surface array data. This paper shows the relation between the site amplifications and the geological conditions, estimated by using the data obtained during the E off Chiba Pref. Earthquake of Dec. 17, 1987 (M=6.7).

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