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Seismic Event in Edo/Tokyo Downtown

江户/东京市中心的地震事件

基本信息

批准号：
08458098
负责人：
SHIMAZAKI Kunihiko
金额：
--
依托单位：
University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至无数据
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-08458098/
关键词：
Tokyo geo-slicer Ansei-Edo earthquake

项目摘要

The oriented 9m deep sections of sediments are recovered from the river bed of the Kyu-Edo river in downtown Tokyo, Japan by using a recently invented 'long geo-slicer", a sampler of columnar soft sediment layrs. Normal-fault rupture with 20cm vertical offset is discovered 30cm below the present river bed. This seimic event is dated as old as 1,800 y.B.P.or youger. An older event is inferred from 1.3m difference in the depth of layr interface at a depth of 7-8m between the two sample sections only a meter apart. This event is dated as old as 2,900-3,700 y.B.P.The normal-fault rupture is oriented in N67E and if this rupture is an echelon fault produced by the underlying active fault suggested by Sugiyama and Endo in 1993 running N100E,the motion of the fault should be left-lateral strike slip. This inference is consistent with the tectonics in this region. This active fault was thought to be relatively inactive and classified as lower C-class fault. The evidence of two seismis event in the past 4,000 years found in our study may seem to be inconsistent with the low activity suggested from relatively small vertical offset of late Quaternary layrs, but our inference that the fault is of strike-slip type would explain the small offset. The significance of the seismic events found in our study would be better assessed when the effect of 2km deep late-Tertiary-Quaternary sediments in Tokyo on surface seismic rupture.

利用新近发明的“长地质切片机”，从日本东京市中心的Kyu-Edo河河床上采集了9 m深的沉积物定向剖面。在现今河床下30 cm处发现了垂直偏移量为20 cm的正断层破裂。这次地震的年代为1,800年前或更早。从两个相距仅一米的样品剖面在7- 8 m深度处的层界面深度相差1.3m推断出一个较早的事件。该事件的年代为2，900 - 3，700 y. B. P.。正断层破裂方向为N67 E，如果该破裂是由Sugiyama和Endo在1993年提出的沿N100 E的下伏活动断层产生的雁行断层，则断层的运动应为左旋走滑。这一推论与本区的构造特征是一致的。该活动断层被认为是相对不活动的，并被归类为低C级断层。我们研究中发现的近4,000年来两次地震事件的证据似乎与晚第四纪地层相对较小的垂直错距所暗示的低活动性不一致，但我们的走滑型断层的推断可以解释这种较小的错距。当东京2km深的晚第三纪-第四纪沉积物对地表地震破裂的影响时，我们研究中发现的地震事件的意义将得到更好的评估。