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Bending-Related Topographic Structures
of the Subducting Plate in the Northwestern
Pacific Ocean
Masao Nakanishi
Abstract
Elongated topographic structures associated with bending of the subducting
oceanic plate along the western Kuril, Japan and northern Izu-Ogasawara trenches,
were investigated using available multibeam bathymetric data. Magnetic anomaly lin-
eations were also reidentified using available geomagnetic data to reveal controlling
factors for strikes of bending-related topographic structures. The new bathymetric
map demonstrates that most of bending-related topographic structures exist in the
oceanward trench slopes deeper than 5,600 m. The map reveals that bending-related
topographic structures are developed parallel to the trench axis or inherited seafloor
spreading fabrics. Detailed identification of magnetic anomalies reveals curved
lineations and discontinuity of lineations associated with propagation ridges.
A trough with elongated escarpments associated with the propagating ridge in mid-
Cretaceous Quiet Period was discovered near the trench-trench-trench triple junction.
Comparison between the detailed bathymetric and magnetic anomaly lineation maps
elucidates that abyssal hill fabrics were reactivated where the angle between abys-
sal hill fabrics and trench axis is less than about 30°. The topographic expression of
bending-related structures are classified into two types according to whether new faults
develop parallel to the trench axis or inherited seafloor spreading fabrics reactivate.
Keywords
Plate bending • Bending-related topographic structure • Deep-sea
trench • Seafloor spreading fabric • Magnetic anomaly lineation
1
Introduction
One of the important properties controlling subduction is the amount of water in
the subducting plate. The release of water from the subducting plate controls the
fluid pressure along the plate interface (Moore and Saffer
2001
) and facilitates the
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