平野の堆積層厚が地震動の卓越周期に及ぽす影響

Memoirs of the Osaka Institute of Technology, Series A Vol. 42, No.1 (1997) pp. 27~47

平野の堆積層厚が地震動の卓越周期に及ぽす影響

大場新太郎・川合 充

・村井信義

Effect of Thickness of Sedimentary Layer in Plain on Predominant Period during Earthquake Ground Motions

by

Shintaro OHBA, Mitsuru KAWAI and Nobuyoshi MURAI Department of Architecture, Faculty of Engineering

(Manuscript received May 30, 1997) Abstract

This paper mainly discusses the influence of the sedimentary thickness on earth­ quake motion characteristics, based on observation records taken from the 1995 Hyogoken-Nanbu Earthquake (Magnitude 7.2) and the 1997 March 16th Aichiken Toubu Earthquake with a magnitude of 5.8 in the Osaka Plain, Nara Basin and nearby plains. Earthquake observation results show that earthquake motion character­ istics in a sedimentary plain surrounded by mountains are greatly influenced by the scale of the plain and magnitude of the earthquake motions.

The analysis of these observations are summarized as follows:

1) The range of longer period above 1.0 sec. is dependent upon the magnitude of earth­ quake motions and the thickness of the sedimentary layer. The predominant period increases with the increase in magnitude and depth of layers.

2) The range of shorter prevailing periods under 1.0 sec. is dependent upon the thick­ ness of sedimentary layer within a depth of approx. 100 meters.

3) The predominant period in the Osaka Plain is longer than that in the Nara Basin, which has a thinner sedimentary layer. In the case of the Hyogoken-Nanbu Earthquake which has a magnitude of 7.2, the predominant period was 4.0 sec. in the Osaka Plain, and 2.5 sec. in the Nara Basin.

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