Studies of seafloor geodetic measurements on observation platforms adapted for sediments

适用于沉积物的观测平台的海底大地测量研究

• 批准号: 12440119
• 负责人: FUJIMOTO Hiromi
• 金额: $ 9.02万
• 依托单位: Tohoku University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 2000
• 资助国家: 日本
• 起止时间: 2000 至 2002
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-12440119/
• 关键词: seafloor geodetic measurement; observation of seafloor crustal movement; tilt measurement; ocean bottom pressure variation; precise point positioning; sedimentary layer; ocean bottom observation platform; deep-sea drill hole; 海底地穀変動; 日本海溝; 深海堀削孔

Subduction zones around Japan are covered with sediments, where precise geodetic measurements for observation of seafloor crustal movements can be difficult. This study aims at examining the stability of seafloor geodetic measurements on the sediments: tilt measurements on a platform with pipes installed in sefloor sediments, precise point positioning and observation of ocean bottom pressure variations with self-landing instrumentsWe have developed two sets of ocean bottom tiltmeter system for deployment by a remotely operated vehicle. The tiltmeter was divided into two parts for operation on the seafloor. A procedure for automatic leveling of the gimbals was improved to reduce consumption of the batteriesWe have confirmed resolution and stability of qaurtz pressure sensor through analysis of ocean bottom pressure data observed by three sensors over a spreading axis of the southern Pacific Rise for 14 manths in 1997-98. All of the sensors recorded pressure increase following the demise of the big 1997-98 El Nino event. The pressure variation suggests an ocean dynamics which can explain an abrupt change of J2 term of the Earth's gravity field. The results also suggest depression of the seafloor near the spreading centerIn July 2002 we could visually observe how a seafloor instrument for point positioning was deployed on the seafloor covered with thick sedimentary layer. The base of the instrument, 1m square of FRP mesh, looked quite stable and sunk only 1cm or less after deployment of 1year. We could confirm that we can carry out precise pressure monitoring and point positioning on thick sediments by using such a base

日本周围的俯冲带覆盖着沉积物，很难进行精确的大地测量以观测海底地壳运动。本研究旨在探讨海底沉积物大地测量的稳定性：在海底沉积物中安装管道的平台上进行倾斜测量，精密点定位和使用自着陆仪器观测海底压力变化。倾斜仪分为两部分，用于在海底操作。通过对1997 ~ 1998年在南太平洋海隆扩展轴上三个压力传感器连续14个月的海底压力观测资料的分析，证实了qaurtz压力传感器的分辨率和稳定性。所有的传感器都记录了1997-98年厄尔尼诺事件结束后的压力增加。这种压力变化反映了一种海洋动力学，它可以解释地球重力场J2项的突变。2002年7月，我们可以直观地观察到海底单点定位仪器是如何部署在覆盖着厚沉积层的海底的。仪器底座为1平方米的玻璃钢网格，看起来相当稳定，部署1年后仅下沉1厘米或更少。可以证实，利用该基座可以对厚层沉积物进行精确的压力监测和点位定位

项目成果

Fujimoto, H.: "On the stability of horizontal positions of acoustic transponders for seafloor geodesy deployed on thick sediment"EOS Trans., AGU. 83・47. F354 (2002)

Fujimoto, H.：“关于部署在厚沉积物上的海底大地测量的声学转发器的水平位置的稳定性”EOS Trans.，AGU 83・47（2002）。

Nishimura,Miura et al.: "Distribution of seismic coupling on the subducting plate baundary"Tectonophysics. 323・. 217-238 (2000)

Nishimura、Miura 等：“俯冲板块边界上的地震耦合分布”Tectonophysicals 323・238（2000）。

藤本博巳,友田好文: "重力からみる地球"東京大学出版会. 172 (2000)

Hiromi Fujimoto、Yoshifumi Tomoda：“从重力角度看地球”，东京大学出版社 172 (2000)。

Fujimoto, H.: "On the stability of horizontal positions of acoustic transponders for seafloor geodesy deployed on thick sediment"EOS Trans.AGU.. 83. G52A-0970 (2002)

Fujimoto, H.：“关于部署在厚沉积物上的海底大地测量的声学转发器水平位置的稳定性”EOS Trans.AGU.. 83. G52A-0970 (2002)

Kanazawa, T.: "Northwest Pacific Seismic Observatory and Hammer Drill Tests"Proc.ODP, Init. Repts.191,1-159:College Station TX 77845-9547,USA.. (CD-ROM). (2001)

Kanazawa, T.：“西北太平洋地震观测站和锤钻测试”Proc.ODP，Init。