Large-scale Seismic Experiments Conducted by Japan Coast Guard in the Northwestern Pacific Plate and the Philippine Sea Plate

Abstract. The southwestern Ryukyu area east of Taiwan Island is an arcuate boundary between Philippine Sea Plate and Eurasian Plate. The topographic features in the area are characterised by (1) a large-scale amphitheatre off Ishigaki Island, just on the estimated epicentre of the tsunamigenic earthquake in 1771, (2) lots of deep sea canyons located north of the amphitheatre, (3) 15–20 km wide fore-arc basin, (4) 15–20 km wide flat plane in the axial area of the trench, (5) E-W trending half grabens located on the fore-arc area, etc., which were revealed by several recent topographic survey expeditions. The diving survey by SHINKAI6500 in the fore-arc area on a spur located 120 km south of Ishigaki Island was carried out in 1992. The site is characterised dominantly by rough topography consisting of a series of steep slopes and escarpments. A part of the surface is eroded due to the weight of the sediment itself and consequently the basement layer is exposed. The site was covered with suspended particles during the diving, due to the present surface sliding and erosion. The same site was resurveyed in 1997 by ROV KAIKO, which confirmed the continuous slope failure taking place in the site. Another example that was observed by KAIKO expedition in 1997 is a largescale mud block on the southward dipping slope 80 km south of Ishigaki Island. This is apparently derived from the shallower part of the steep slope on the southern edge of the fan deposit south of Ishigaki Island. The topographic features suggest N-S or NE-SW tensional stress over the whole study area. In this sense, the relative motion between the two plates in this area is oblique to the plate boundary. So, the seaward migration of the plate boundary may occur due to the gravitational instability at the boundary of the two different lithospheric structures. This is evidenced by a lack of accretionary sediment on the fore-arc and the mechanism of a recent earthquake which occurred on 3 May 1998 in the Philippine Sea Plate 250 km SSE of Ishigaki Island.

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Geometry and relative motion of the Philippine Sea Plate and Pacific Plate beneath the Kanto-Tokai District, Japan

Journal of Geophysical Research Atmospheres ◽

10.1029/91jb02567 ◽

1992 ◽

Vol 97 (B1) ◽

pp. 489 ◽

Cited By ~ 189

Author(s):

Mizuho Ishida

Keyword(s):

Relative Motion ◽

Pacific Plate ◽

Philippine Sea Plate ◽

Philippine Sea

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Tectonic implications of carbonate deposits on the eastern slope of the Hahajima Seamount in the collision zone between the Izu–Bonin Arc on the Philippine Sea Plate and the Ogasawara Plateau on the Pacific Plate

Island Arc ◽

10.1111/iar.12368 ◽

2020 ◽

Vol 29 (1) ◽

Author(s):

Jun Miyata ◽

Hideko Takayanagi ◽

Akimasa Ishigaki ◽

Naoto Hirano ◽

Satoshi Shiokawa ◽

...

Keyword(s):

Pacific Plate ◽

Philippine Sea Plate ◽

Eastern Slope ◽

Philippine Sea ◽

Collision Zone ◽

Tectonic Implications ◽

The Pacific ◽

Carbonate Deposits

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Origin of the Indian Ocean-type isotopic signature in basalts from Philippine Sea plate spreading centers: An assessment of local versus large-scale processes

Journal of Geophysical Research Atmospheres ◽

10.1029/98jb02052 ◽

1998 ◽

Vol 103 (B9) ◽

pp. 20963-20979 ◽

Cited By ~ 129

Author(s):

Rosemary Hickey-Vargas

Keyword(s):

Indian Ocean ◽

Large Scale ◽

Isotopic Signature ◽

Philippine Sea Plate ◽

Philippine Sea ◽

The Indian Ocean ◽

Spreading Centers ◽

Plate Spreading

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The strength of large-scale plate boundaries: Constraints from the dynamics of the Philippine Sea plate since ∼5Ma

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2012.09.018 ◽

2012 ◽

Vol 357-358 ◽

pp. 21-30 ◽

Cited By ~ 18

Author(s):

Giampiero Iaffaldano

Keyword(s):

Large Scale ◽

Philippine Sea Plate ◽

Plate Boundaries ◽

Philippine Sea

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The Predictability of Large-Scale, Short-Period Ocean Variability in the Philippine Sea and the Influence of Such Variability on Long-Range Acoustic Propagation

10.21236/ada617881 ◽

2014 ◽

Author(s):

Brian Dushaw

Keyword(s):

Long Range ◽

Large Scale ◽

Acoustic Propagation ◽

Ocean Variability ◽

Philippine Sea ◽

Short Period

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Configuration and structure of the Philippine Sea Plate off Boso, Japan: constraints on the shallow subduction kinematics, seismicity, and slow slip events

Earth Planets and Space ◽

10.1186/s40623-019-1090-y ◽

2019 ◽

Vol 71 (1) ◽

Cited By ~ 2

Author(s):

Aki Ito ◽

Takashi Tonegawa ◽

Naoki Uchida ◽

Yojiro Yamamoto ◽

Daisuke Suetsugu ◽

...

Keyword(s):

Receiver Function ◽

Function Analysis ◽

Philippine Sea Plate ◽

Slow Slip ◽

Low Velocity ◽

Slow Slip Events ◽

Philippine Sea ◽

Receiver Function Analysis ◽

Eastern Edge ◽

Upper Boundary

Abstract We applied tomographic inversion and receiver function analysis to seismic data from ocean-bottom seismometers and land-based stations to understand the structure and its relationship with slow slip events off Boso, Japan. First, we delineated the upper boundary of the Philippine Sea Plate based on both the velocity structure and the locations of the low-angle thrust-faulting earthquakes. The upper boundary of the Philippine Sea Plate is distorted upward by a few kilometers between 140.5 and 141.0°E. We also determined the eastern edge of the Philippine Sea Plate based on the delineated upper boundary and the results of the receiver function analysis. The eastern edge has a northwest–southeast trend between the triple junction and 141.6°E, which changes to a north–south trend north of 34.7°N. The change in the subduction direction at 1–3 Ma might have resulted in the inflection of the eastern edge of the subducted Philippine Sea Plate. Second, we compared the subduction zone structure and hypocenter locations and the area of the Boso slow slip events. Most of the low-angle thrust-faulting earthquakes identified in this study occurred outside the areas of recurrent Boso slow slip events, which indicates that the slow slip area and regular low-angle thrust earthquakes are spatially separated in the offshore area. In addition, the slow slip areas are located only at the contact zone between the crustal parts of the North American Plate and the subducting Philippine Sea Plate. The localization of the slow slip events in the crust–crust contact zone off Boso is examined for the first time in this study. Finally, we detected a relatively low-velocity region in the mantle of the Philippine Sea Plate. The low-velocity mantle can be interpreted as serpentinized peridotite, which is also found in the Philippine Sea Plate prior to subduction. The serpentinized peridotite zone remains after the subduction of the Philippine Sea Plate and is likely distributed over a wide area along the subducted slab.

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