Upper mantle and crustal seismic structure beneath the Northwestern Pacific Basin using a seafloor borehole broadband seismometer and ocean bottom seismometers

Shinohara, Masanao; Fukano, T.; Kanazawa, Toshihiko; Araki, Eiichiro; Suyehiro, Kiyoshi; Mochizuki, Masahito; Nakahigashi, Kazuo; Yamada, Tomoaki; Mochizuki, Kimihiro

doi:10.1016/j.pepi.2008.07.039

Cited by 82 publications

(135 citation statements)

References 41 publications

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“…3. The differences between our models and the model by Shinohara et al (2008) suggest that the crust-mantle transition zone suggested by White et al (1992) accounts for half of the normal ocean crustal structures in their dataset which exhibits first-order velocity discontinuities, with the other half displaying velocity gradients. The uppermost mantle structure along MTr6 is characterized by a large heterogeneity immediately under the Moho.…”

Section: Oceanic Crust and Uppermost Mantle Structurecontrasting

confidence: 60%

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Seismic structures of the 154–160 Ma oceanic crust and uppermost mantle in the Northwest Pacific Basin

2010

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We present detailed P-wave velocity models for the Northwest Pacific Basin which were produced in 154-160 Ma at a high seafloor spreading half-rate of >8 cm/yr and have not been appreciably deformed by tectonic or igneous activity since then. We carried out wide-angle seismic experiments on two crossing survey lines which are respectively parallel and perpendicular to paleomagnetic lineations. The seismic crustal models for both lines are almost identical and homogeneous along these lines. The crust consists of an upper layer (Layer 2) with a P-wave velocity V p = 2.5-6.8 km/s and a thickness of 1.3-2.2 km, and a lower layer (Layer 3) with a velocity of 6.8-7.1 km/s and a thickness of 4.6-5.9 km. These characteristics indicate that the crust beneath the survey line has a standard oceanic crustal structure. The structure of the uppermost mantle of the line parallel to the seafloor spreading direction exhibits considerable V p heterogeneity within 5 km immediately below the Moho and shows an unusually high V p of 8.5-8.7 km/s. The P n velocity for the perpendicular line is 7.9 km/s, and the magnitude of the velocity anisotropy for the uppermost mantle amounts to a large value of 7-10%.

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Section: Oceanic Crust and Uppermost Mantle Structurecontrasting

confidence: 60%

“…Recently, Shinohara et al (2008) reported a crustal structure in the northern part of the Nortwest Pacific Basin (Fig. 1) on the basis of observations obtained through a seafloor borehole broadband seismometer.…”

Section: Oceanic Crust and Uppermost Mantle Structurementioning

confidence: 99%

Seismic structures of the 154–160 Ma oceanic crust and uppermost mantle in the Northwest Pacific Basin

2010

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“…It is believed that the uppermost mantle in the Northwestern Pacific Basin exhibits a seismic anisotropy (e.g. Shinohara et al, 2008). The az- imuthal anisotropy in the oceanic upper mantle appears to be aligned with the direction of spreading at the time of crustal generation rather than in the direction of present plate motions (e.g.…”

Section: Resultsmentioning

confidence: 99%

P-wave velocity structure in the southernmost source region of the 2011 Tohoku earthquakes, off the Boso Peninsula, deduced by an ocean bottom seismographic survey

et al. 2012

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We present the result of a seismic experiment conducted using ocean bottom seismometers and controlled sources in the region off Ibaraki and the Boso Peninsula. This region is the southern edge of the rupture zone of the 2011 off the Pacific coast of Tohoku Earthquake. We estimated the P-wave seismic velocity structure beneath the profile using a 2-D ray-tracing method. The crustal structure in the southern area is more heterogeneous than that of the northern area. This heterogeneity is thought to be related with subducting the Philippine Sea plate (PHS). The plate boundary between the landward plate and the Pacific plate (PAC) is positioned at depths of 20 km at a distance of 170 km from the southern end of the profile. The subducting PHS is imaged on the southern part of the profile. However, we could not obtain a distinct image of the contact zone of PHS and PAC. The contact zone of PHS and PAC is estimated to have a large heterogeneity resulting from strong deformation due to the collision of the two plates. We infer that the termination of the rupture, and the large afterslip in the collision region, are caused by this strong heterogeneity.

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“…We assumed an isotropic ocean and crust at depths of 0-13.3 km, and anisotropic mantle at depths of 13.3-220 km. As the azimuthal anisotropy of P-wave velocity slightly affects the azimuthal anisotropy of surfacewave velocity, we further assumed that the intensity of P-wave anisotropy is 1.3 times the intensity S-wave anisotropy based on the ratio between Pn-and Sn-wave anisotropy obtained in the northwest of Shatsky Rise by Shinohara et al (2008).…”

Section: Intensity Of Azimuthal Anisotropymentioning

confidence: 99%

Estimation of azimuthal anisotropy in the NW Pacific from seismic ambient noise in seafloor records

Takeo¹,

Forsyth

Weeraratne

et al. 2014

Geophysical Journal International

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S U M M A R YWe analysed background surface waves in seismic ambient noise by cross-correlating continuous records of eight ocean bottom seismometers and nine differential pressure gauges deployed in the northwestern Pacific Ocean by the PLATE project. After estimating the clock delay and instrumental phase responses of differential pressure gauges by using cross-correlation functions, we measured average phase velocities in the area of the array for the fundamental-, first higher-and second higher-mode Rayleigh waves, and the fundamental-mode Love waves at a period range of 3-40 s by waveform fitting. We then measured phase-velocity anomalies of fundamental-mode and first higher-mode Rayleigh waves for each pair of stations at a period range of 5-25 s, and corrected the effect of variation in water-depths. The seismic anomalies imply the presence of strong azimuthal anisotropy beneath the eastern part of array. The direction of maximum velocity is approximately N35• E in the fossil seafloor spreading direction perpendicular to magnetic lineations from the ancient triple junction at this location. The peak-to-peak intensity of shear-wave velocity anisotropy in the mantle is ∼7 per cent.

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Upper mantle and crustal seismic structure beneath the Northwestern Pacific Basin using a seafloor borehole broadband seismometer and ocean bottom seismometers

Cited by 82 publications

References 41 publications

Seismic structures of the 154–160 Ma oceanic crust and uppermost mantle in the Northwest Pacific Basin

Seismic structures of the 154–160 Ma oceanic crust and uppermost mantle in the Northwest Pacific Basin

P-wave velocity structure in the southernmost source region of the 2011 Tohoku earthquakes, off the Boso Peninsula, deduced by an ocean bottom seismographic survey

Estimation of azimuthal anisotropy in the NW Pacific from seismic ambient noise in seafloor records

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