| Budget Amount *help |
¥2,300,000 (Direct Cost: ¥2,300,000)
Fiscal Year 1992: ¥300,000 (Direct Cost: ¥300,000)
Fiscal Year 1991: ¥2,000,000 (Direct Cost: ¥2,000,000)
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| Research Abstract |
The Osaka Plain is surrounded by mountainous regions and is located in the northeast of an oval-shaped basin, comprising part of the Osaka Bay, with a 40 km minor axis and 80 km major axis. The earthquake motions in the Osaka Plain are greatly influenced by the topographical conditions and the ground conditions
This report studies the duration time, predominant period and amplification characteristics of earthquake motions in the reclaimed ground, based on the data gathered through earthquake observation.
The discussion revealed the following :
(1) Duration time
The duration of earthquake motions in the Osaka Plain varies with the horizontal distance between the surrounding mountains and the location in the plain ; the duration time is short in areas on the border between the mountains and plain, while it is markedly longer in the central part of the plain. This variation in the duration of earthquake motions is not caused by the difference in the conditions of the surface layer, such as that between a diluvial layer and an alluvial layer. It results from the fact that the synthesis of S waves from below, corresponding to main motions, and surface waves propagated horizontally through the sedimentary layer, corresponding to delayed motions.
(2) Predominant period
The short periods (less than approx. 1 second) prevail in the portion of the wavefrom corresponding to main motions. The predominant periods shorter than approx. 1 second reflect the structure of the uppermost part of the ground. The periods longer than approx. 1 second mainly prevail at the portion of the wavefrom corresponding to the delayed motions.
(3) Amplification characteristic
In the periodic band shorter than approx. 1 second, the amplification characteristics of earthquake motions in the reclaimed ground vary conspicuously according to the structure of subsurface layers, up to approx. 60 m under the surface.
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