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Quantitative assessment of deformation of upper crust based on paleomagnetism of widespread tephra and large-scale pyroclastic flow deposit

基于广泛分布的火山灰和大型火山碎屑流沉积的古地磁定量评估上地壳变形

基本信息

批准号：
17540438
负责人：
ITOH Yasuto
金额：
$ 2.24万
依托单位：
Osaka Prefecture University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2005
资助国家：
日本
起止时间：
2005 至 2006
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-17540438/
关键词：
geophysics natural disaster earthquake paleomagnetism active fault geodesy geology disaster prevention

项目摘要

In this study, field survey was conducted for widespread tephra, large-scale pyroclastic flow deposits and a Quaternary volcano in the central part of Honshu Island, Japan. Samples for paleomagnetic measurements were obtained from 39 sites. Remanent magnetization was measured by a spinner magnetometer, and stability of remanence was evaluated by progressive thermal and alternating-field demagnetization. Progressive acquisition of isothermal remanent magnetization (IRM) was conducted using a pulse magnetizer in order to estimate ferromagnetic minerals in rocks, and the estimation was verified through thermal demagnetization of orthogonal IRM. Available site-mean paleomagnetic directions were compiled for determination of high strain area, which was correlated with a deformation zone recently detected through geodetic studies of nationwide GPS array. Along with these study, fault motion and basin-forming history over 10 m.y. in an arc-arc junction (Hokkaido) and a seismogenic subduction zone (Pacific coast of northeast Japan) were clarified on the basis of interpretation of reflection seismic data, which gave a significant clue to understand tectonics in central Japan. We have precisely assessed short-term crustal deformation utilizing paleomagnetic method, which is generally applied for long-standing cumulative deformation between plates.

本研究对日本本州岛中部广泛分布的火山灰、大规模火山碎屑流沉积和一座第四纪火山进行了野外调查。从39个地点获得了古地磁测量样品。剩磁由旋转磁强计测量，剩磁的稳定性进行了评估，通过渐进的热和交变磁场退磁。为了估算岩石中的铁磁性矿物，采用脉冲磁化仪进行等温剩磁（reversization magnetization，简称reversization）的逐步采集，并通过正交磁化曲线的热退磁验证了估算结果。汇编了现有的场地平均古地磁方向，用于确定高应变区，该高应变区与最近通过全国GPS阵列的大地测量研究发现的变形区相关联。沿着这些研究，对1000万年以来的断裂运动和成盆历史进行了研究。通过对反射地震资料的解释，阐明了日本中部弧-弧结合带（北海道）和孕震俯冲带（日本东北部太平洋沿岸）的构造活动，为认识日本中部的构造提供了重要线索。利用古地磁方法对地壳短期形变进行了精确的估算，该方法通常用于研究板块间长期累积形变。