2004 Fiscal Year Final Research Report Summary
Research on the tectonics of the southeastern Philippine Sea based on GPS observations
| Project/Area Number |
14403003
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 海外学術 |
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| Research Field |
固体地球物理学
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| Research Institution | The University of Tokyo |
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Principal Investigator |
KATO Teruyuki The University of Tokyo, Earthquake Research Institute, Professor, 地震研究所, 教授 (80134633)
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| Co-Investigator(Kenkyū-buntansha) |
MATSUSHIMA Takeshi Kyushu University, Graduate School of Science, Associate Professor, 大学院・理学研究院, 助教授 (40222301)
TABEI Takao Kochi University, Faculty of Science, Professor, 理学部, 教授 (40207220)
NAKADA Setsuya The University of Tokyo, Earthquake Research Institute, Professor, 地震研究所, 教授 (60128056)
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| Project Period (FY) |
2002 – 2004
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| Keywords | GPS / The Northern Marian Islands / back-arc / back-arc spreading / plate motion / Philippine Sea / Anatahan Island / eruption |
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| Research Abstract |
We have repeated GPS observations for darifying tectonic motion in the Northern Mariana Islands, Commonwealth of the Northern Mariana Islands. Moreover, we investigated the volcanic activity of Anatahan Island that began eruption in May 2003 for the first time in the human history. GPS observations were conducted in January 2003, July 2003 and May-Jun 2004. The obtained data were analyzed taking earlier data into consideration. Considering that the northernmost three islands were not been observed more than once, we extensively made observations in those three islands, namely, Asencion, Maug and Uracus. Results show that the effect of back-arc spreading in the Mariana Trough is eminent in the region. However, at the northern three islands, residual vectors that indicate effects of back-arc spreading show somewhat diverging vectors. The effect of back-arc spreading is not very eminent. This is probably due to short observation time of only one year. We should make more detailed analysis
… More
of the data. In addition, we may have to repeat GPS observations in the future to obtain more reliable results.
Anatahan volcano began erupting in May-Jun 2003. A series of subplinian explosive eruptions of andesite magma began at the Eastern Crater in the eastern part of the summit caldera on the evening of 10 May. Brown tephra was sent mainly westward by strong winds. Small-scale pyroclastic surges were discharged eastward outside the caldera in late May. An andesite lava dome that had once filled the inner crater was fragmented by phreatomagmatic explosions in the middle of June. The phreatomagmatic explosions probably occurred due to interaction of the magma lead with ground water around the crater, and abundant very fine ash ("gray tephra") was discharged within the caldera and over most of the island. The volume of eruption products of the May-June eruption was estimated to be 1.4x10^7 m^3 dense-rock-equivalent. Erupted pumices and lava are aphyric andesite and are variously colored depending on their vesicularity. The SiO2 contents of erupted materials decreased slightly with time. The fine gray ash is depleted in alkalies, probably due to leaching by acid hydrothermal fluids during explosions. Seismic activity resumed in late March 2004, and small strombolian-like explosions were repeated in May and June 2004. About hard of the inner crater was filled with new scoria and lava. Less
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Research Products
(9 results)
