Geophysical Study on Hotspot Volcanisim in African Continent

非洲大陆热点火山活动的地球物理研究

• 批准号: 04041018
• 负责人: HAMAGUCHI Hiroyuki
• 金额: $ 24.32万
• 依托单位: Faculty of Science, Tohoku University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for international Scientific Research
• 财政年份: 1992
• 资助国家: 日本
• 起止时间: 1992 至 1994
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-04041018/
• 关键词: East African Rift Valley; Volcanic Activity; Hotspot; Eruption; Earth's Deep Interior; Earthquakes; Africa; Earth's Core; 噴火活動; 地球物理学; 火山噴火; 地震観測; ザイール

(1) We analyzed SmKS and PKP waves recorded by the GDSN in order to survey the lateral heterogeneity in the lower mantle and at the top of the Earth's core. The spherical harmonic analysis revealed that the hemishperical (degree 1) pattern in the heterogeneities predominants at the top of the Earth's outer core and inner core beneath the African continent.(2) We developed the small and low-power data logger with the precise GPS clock. This equipments were applied successfully to the field observations in the volcanic regions in Africa.(3) The Nyiragongo volcano in eastern Zaire presents the highest potential threat to human lives in Goma region, partly because of the abnormal increasing population fleeing from Rwanda and partly because of the lack of mitigation plan by the local government.(4) The recent volcano-magmatic activity of Nyiragongo and Nyamuragira are summarized as follows ;(a) After the initial episode of eruption in the lava-lake, we observed at least 37 eruptive episodes in the period from June, 1994 to February, 1995. The most significant features in the episodic pattern are not only the intermittent appearance of active periods but also the change of their tempo that happened at the middle of December, 1994. Since January, 1995, the intermittency has declined and continuous features of tremors with small amplitudes became predominant, which suggests that dike-like ocnduit changed to the open conduit system.(b) The seismic activity shows rather concentrated features at the depth of about 15 km just beneath the Nyiragongo carter. The earthquakes with very shallow focal depths were not located closely to the Nyiragongo crater.(c) The pattern of continuously recorded tilt vector indicates that Nyiragongo has slowly inflated since the beginning of eruption. This inflation was probably caused by the storage of excess magma in the very shallow reservoir or in the lava lake.

(1)为了研究下地幔和地核顶部的横向不均匀性，我们分析了GDSN记录的SmKS和PKP波。球谐分析表明，在地球的外核顶部和非洲大陆下面的内核的不均匀性的半球形（1度）模式占主导地位。(2)我们开发了小型低功耗的数据记录仪与精确的GPS时钟。该设备已成功地应用于非洲火山区的野外观测。(3)扎伊尔东部的尼拉贡戈火山对戈马地区的人的生命构成最大的潜在威胁，部分原因是逃离卢旺达的人口异常增加，部分原因是当地政府缺乏缓解计划。(4)尼拉贡戈和尼亚穆拉吉拉火山岩浆活动的最新情况总结如下：（a）在熔岩湖的第一幕喷发之后，我们观察到至少37个喷发事件在1994年6月至1995年2月期间。其最显著的特征不仅是活动期的间歇性出现，而且是其克里思的变化发生在1994年12月中旬。自1995年1月以来，地震活动的不稳定性下降，小振幅地震的连续性特征占主导地位，这表明岩墙式管道系统已转变为开放式管道系统。(b)地震活动在尼拉贡戈卡特之下约15公里深处显示出相当集中的特征。震源深度很浅的地震并不靠近尼拉贡戈火山口。(c)连续记录的倾斜矢量模式表明，尼拉贡戈火山自喷发开始以来一直在缓慢膨胀。这种膨胀可能是由于在非常浅的水库或熔岩湖中储存了过量的岩浆造成的。

项目成果

浜口 博之: "東アフリカ台地と火山活動" 月刊地球,. 14. 713-717 (1992)

Hiroyuki Hamaguchi：“东非高原和火山活动”月刊地球，14。713-717（1992）

Nishimura, T., Morita, Y.and Hamaguchi, H.: "Development of small data logger with GPS clock" J.Seism.Soc.Japan, Zisin, II. 47. 79-83 (1994)

Nishimura, T.、Morita, Y. 和 Hamaguchi, H.：“带 GPS 时钟的小型数据记录器的开发”J.Seism.Soc.Japan、Zisin, II。

Morita, Y.and Nishimura, T.: "Development of precise clock for seismological observation using GPS receiving board" J.Seis.Soc.Japan, ZISIN II. 46. 67-74 (1993)

Morita, Y. 和 Nishimura, T.：“使用 GPS 接收板开发用于地震观测的精确时钟” J.Seis.Soc.Japan，ZISIN II。

TANAKA,S.and HAMAGUCHI,H.: "Velocities and chemical stratification in the outermost core" Jour.Geomag.Geoelect.(1993)

TANAKA,S. 和 HAMAGUCHI,H.：“最外层核心的速度和化学分层”Jour.Geomag.Geoelect.(1993)

S.Tanaka and H.Hamaguchi: "Velocities and chemical stratification in the outermost Core" Journal Geomag.Geoelectr.45. 1287-1301 (1993)

S.Tanaka 和 H.Hamaguchi：“最外层核心的速度和化学分层”Journal Geomag.Geolectr.45。