High-resolution subducting-slab structure beneath northern Honshu, Japan, revealed by double-difference tomography
- Haijiang Zhang1,
- Clifford H. Thurber1,
- David Shelly2,
- Satoshi Ide3,
- Gregory C. Beroza4 and
- Akira Hasegawa5
- 1Department of Geology and Geophysics, University of Wisconsin, Madison, Wisconsin 53706, USA
- 2Department of Geophysics, Stanford University, Stanford, California 94305, USA
- 3Department of Earth and Planetary Science, University of Tokyo, Tokyo 113-0033, Japan
- 4Department of Geophysics, Stanford University, Stanford, California 94305, USA
- 5Research Center for Prediction of Earthquakes and Volcanic Eruption, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
Abstract
The high-resolution seismic velocity structure of the subducting slab beneath northern Honshu, Japan, has been obtained by double-difference tomography, capitalizing on the existence of two planes of seismicity. The upper plane lies in the region with average to high Vp/Vs ratios (1.72–1.85), which may correspond to the transformations of metabasalt and metagabbro to blueschist. The lower plane is associated with very low Vp/Vs ratios (1.6–1.7), in sharp contrast with high Vp/Vs ratios (∼1.8–1.85) in the region between the two planes. These features may be explained by forsterite-enstatite-H2O formation from serpentine dehydration in the lower plane and partial hydration of the region between the two planes. Our results provide direct constraints for petrologic modeling of the subducting slab.
Footnotes
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↵GSA Data Repository item 2004058, Figure DR1 (the square root of the derivative weight sum using the event pairs within 10 km and 20 km of each other), and Figures DR2–DR4 (synthetic tests), is available online at http://www.geosociety.org/pubs/ft2004.htm, or on request from editing{at}geosociety.org or Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301-9140, USA.
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- Accepted December 19, 2003.
- Received October 13, 2003.
- Revision received December 18, 2003.
- Geological Society of America
