A Study on the Effect of Deep Sedimentary Layrs below the Plain on Earthquake Motions

本文利用1995年小古根-南部7.2级地震和1997年3月16日大阪平原、奈良盆地及近平原地区发生的爱知根头部5.8级地震的观测资料，研究了深层沉积层对地震运动特征的影响。地震观测结果表明，在被山脉包围的沉积平原上，地震运动特征受平原规模和震级的影响较大。对这些观测结果的分析总结如下：1)1.0秒以上较长周期的范围取决于地震运动的震级和沉积层的厚度。优势期随层数和层深的增加而增加。(2) 1.0秒以下较短盛行期的范围取决于沉积层的厚度。100米。3)大阪平原的优势期比奈良盆地的优势期长，奈良盆地的沉积层较薄。在7.2级的小古根-南部地震中，大阪计划的主导周期为4.0秒，奈良盆地的主导周期为2.5秒。4)沉积平原地震运动的持续时间取决于平原的大小，特别是面积。大阪平原的持续时间是面积较小的奈良盆地的两倍以上。

This study mainly covered the influence of deep sedimentary layrs on earthquake 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 nearly plains. Earthquake observation results show that earthquake motion characteristics in a sedimentary plain surrounded by mountains are greatly influenced by the scale of 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 earthquake motions and the thickness of the sedimentary layr. The predominant period increases with the increase in magnitude and depth of layrs.2)The range of shorter prevailing periods under 1.0 sec.is dependent upon the thickness of sedimentary layr 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 layr. 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 Plan, and 2.5 sec.in the Nara Basin.4)The duration time of earthquake motion in a sedimentary plain depends on size of plain particularly the area. The duration time in the Osaka Plain is more than twice that of the Nara Basin, which has a smaller area.