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Gravity anomaly and the geoid height at plate boundaries - classification of strain accumulation process and its geophysical interpretation

重力异常与板块边界大地水准面高度——应变累积过程分类及其地球物理解释

基本信息

批准号：
04452062
负责人：
OKUBO Shuhei
金额：
$ 0.32万
依托单位：
University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1992
资助国家：
日本
起止时间：
1992 至 1993
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-04452062/
关键词：
Geoid Plate tectonics Gravity anomaly Sea-level

项目摘要

1.Theoretical work.We find an intriguing reciprocity relations between the static deformation excited by a point dislocation in a SNREI earth and those generated by external forces, such as tidal force, surface loading and surface shear forces. the relations enable us to compute the coseismic potential change in a spherically symmetric earth model for the March 28, 1964 Alaska earthquake(mW=9.2). We consider two cases : (1) one is with a barrier where no slip occurs on the fault plane and (2) the other without it. Numerical results clearly indicated that the geoid swells above the subsurface fault while giving a notch over the hidden barrier. Although order of magnitude of these changes are marginal for the present satellite altimetry, there is a good chance of detecting such co-seismic geoid changes if we carefully process satellite altimeter data.2. Analysis of observational dataWe analyzed a gravity anomaly around the North-Izu Fault System (NIFS), Japan Numerical simulation using the theory of coseismic gravity change with geological fault parameters reproduced the local gravity anomaly excellently : positive anomalies over a compressed zone.while negative anomalies over the dilated areas. We conclude the resultant gravity anomaly is the product of repeated coseismic gravity change during a geological timescale because earthquakes will occur on the same fault with the same scheme. However small a coseismic gravity change may be, it is likely to pile up in a systematic way over a long time.

1.理论工作。我们发现SNREI中点位错引起的静态变形与潮汐力、表面载荷和表面剪切力等外力引起的静态变形之间存在有趣的互易关系。这些关系使我们能够在球对称地球模型中计算1964年3月28日阿拉斯加地震（mW=9.2）的同震位势变化。我们考虑两种情况：(1)一种是有障碍，在断层面上没有滑动；(2)另一种是没有障碍。数值结果清楚地表明，大地水准面在地下断层上方膨胀，同时在隐蔽的屏障上方形成一个缺口。虽然这些变化的数量级对于目前的卫星测高来说是微不足道的，但如果我们仔细处理卫星测高数据，就有很好的机会探测到这种同震大地水准面变化。观测资料分析利用同震重力变化理论和地质断层参数进行数值模拟，较好地再现了局部重力异常：压缩带上的正异常。而扩张区域呈阴性异常。由于地震会以相同的方式发生在同一断层上，因此得出的重力异常是同一地质时间尺度内重复同震重力变化的产物。无论同震重力变化多么小，它都可能在很长一段时间内以系统的方式堆积起来。