2006 Fiscal Year Final Research Report Summary
Marine magnetotelluric experiment across the central Mariana subduction-arc-back arc system
| Project/Area Number |
15340149
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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 | 一般 |
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| Research Field |
Solid earth and planetary physics
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| Research Institution | Kobe University |
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Principal Investigator |
SEAMA Nobukazu Kobe University, Research Center for Inland Seas, Associate Professor, 内海域環境教育研究センター, 助教授 (30270862)
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| Co-Investigator(Kenkyū-buntansha) |
UTADA Hisashi University of Tokyo, Earthquake Research Institute, Professor, 地震研究所, 教授 (70134632)
GOTO Tada-nori Japan Agency for Marine-Earth Science and Technology, Institute for Research on Earth Evolution, Researcher, 地球内部変動研究センター, 研究員 (90303685)
BABA Kiyoshi University of Tokyo, Earthquake Research Institute, Research Associate, 地震研究所, 助手 (70371721)
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| Project Period (FY) |
2003 – 2006
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| Keywords | Subduction Zone / Back-arc Basin / Central Mariana area / Upper mantle conductivity structure / Ocean Bottom Electro-Magnetometers / Magnetotelluric method |
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| Research Abstract |
We carried out a marine magnetotelluric transect across the central Mariana subduction-arc-back arc system using ocean bottom electro-magnetometers (OBEMs), ocean bottom electrometers (OBEs), and ocean bottom magnetometers (OBMs) to provide the electrical conductivity structure of the Mariana island-arc system extending from the Pacific ocean to the West Mariana Ridge (remnant arc) through the Marina Trough. Deployments of 33 OBEMs, 7 OBMs, and 7 OBEs were made at 40 sites across the central Mariana subduction-arc-back arc system during KR05-17 cruise. Observations using the instruments were made from December 2005 up to the recovery in September 2006. We successfully recovered 28 OBEMs, 7 OBMs, and 6 OBEs at 35 sites during KR06-12 cruise. We are still analyzing these data to estimate the upper mantle electrical conductivity structure, because the observation was delayed. But, these data will provide a comprehensive image of the conductivity structure for the central Mariana subduction-arc-back arc system, because the observation sites are so dense.
We analyzed previous 9 OBEM data obtained from the same area. The resulting electrical resistivity structure shows an increase in conductivity at depths of about 70 km beneath the Mariana Trough and anisotropy at deeper depth. The low conductivity structure near Mariana Trough spreading axis implies that the onset of melting in the Mariana Trough back-arc basin is deeper than that of the typical MORB source region.
Consideration of the effect of seafloor topography on ocean bottom magnetotelluric data is needed to estimate a reliable conductivity structure. We evaluated three different correction equations to correct the effect of seafloor topography with forward modeling, and we indicate the most an appropriate correction method based on a series of synthetic tests.
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