Seismic structure of the northern end of the Ryukyu Trench subduction zone, southeast of Kyushu, Japan

Nishizawa, Azusa; Kaneda, Kentaro; Oikawa, Mitsuhiro

doi:10.1186/bf03352942

Cited by 27 publications

(27 citation statements)

References 9 publications

(12 reference statements)

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“…However, the depth of 10 km on our seismic lines to the northeast of ECr11 moves toward the trench axis. Previous results for lines KPr1, DAr5, and DAr2 in the northernmost trench area (Nishizawa et al 2009) also support trenchward positions of the 10-km contour.…”

Section: Subduction Of the Philippine Sea Platesupporting

confidence: 59%

“…Another characteristic in the gravity map is that there are two low gravity anomaly belts parallel to the trench. One of the low gravity belts is along the trench axis, and the other one is in the (Nishizawa et al 2009). A non-tuned airgun array with a capacity of 6000 (1500 × 4) cubic inch (98.3 L) was shot for the refraction survey and a 1050 (350 × 3) cubic inch (17.2 L) airgun cluster was used for the multichannel reflection survey.…”

Section: Introductionmentioning

confidence: 99%

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Variations in seismic velocity distribution along the Ryukyu (Nansei-Shoto) Trench subduction zone at the northwestern end of the Philippine Sea plate

Nishizawa

Kaneda

Oikawa

et al. 2017

Earth Planets Space

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The Ryukyu (Nansei-Shoto) island arc-trench system, southwest of Japan, is formed by the subduction of the Philippine Sea (PHS) plate. Among the subduction zones surrounding the Japan Islands, the Ryukyu arc-trench system is unique in that its backarc basin, the Okinawa Trough, is the area with current extensively active rifting. The length of the trench is around 1400 km, and the geological and geophysical characteristics vary significantly along the trench axis. We conducted multichannel seismic (MCS) reflection and wide-angle seismic surveys to elucidate the along-arc variation in seismic structures from the island arc to the trench regions, shooting seven seismic lines across the arctrench system and two along-arc lines in the island arc and the forearc areas. The obtained P-wave velocity models of the Ryukyu arc crust were found to be heterogeneous (depending on the seismic lines), but they basically consist of upper, middle, and lower crusts, indicating a typical island arc structure. Beneath the bathymetric depressions cutting the island arc-for example, the Kerama Gap and the Miyako Saddle-the MCS record shows many across-arc normal faults, which indicates the presence of an extensional regime along the island arc. In the areas from the forearc to the trench, the subduction of the characteristic seafloor features on the PHS plate affects seismic structures; the subducted bathymetric high of the Amami Plateau is detected in the northern trench: the Luzon-Okinawa fracture zone beneath the middle and southern trenches. There are low-velocity (<~4.5 km/s) wedges along the forearc areas, except for off Miyako-jima Island. The characteristic high gravity anomaly at the forearc off Miyako-jima Island is caused not by a bathymetric high of a large-scale accretionary wedge but by shallower materials with a high P-wave velocity of ~4.5 km/s.

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Section: Subduction Of the Philippine Sea Platesupporting

confidence: 59%

Section: Introductionmentioning

confidence: 99%

Variations in seismic velocity distribution along the Ryukyu (Nansei-Shoto) Trench subduction zone at the northwestern end of the Philippine Sea plate

Nishizawa

Kaneda

Oikawa

et al. 2017

Earth Planets Space

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“…The Kyushu Mountains are the northern extension of KyushuPalau Ridge. Nishizawa et al (2009) showed the existence of a thick oceanic crust related to the subducting KyushuPalau Ridge in the eastern part of the Hyuganada region. They observed a low-velocity zone (V p = 6.0-6.8 km/s) at the oceanic middle crust (10-15 km depth).…”

Section: Beneath the Kyushu Mountainsmentioning

confidence: 99%

Velocity structure in the crust beneath the Kyushu area

et al. 2010

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We present high-resolution three-dimensional tomographic images of the crust beneath the entire Kyushu arc, and particularly the western portion. Our results reveal a velocity anomaly that correlates well with an upper crustal gravity anomaly. Signi cant low-velocity anomalies exist beneath the Miyazaki plane and along the Beppu-Shimabara Graben. Another extensive low-velocity region near the bottom of the crust is located just below the volcanic front and between active volcanoes. The low-velocity anomalies exhibit low V p and V p /V s characteristics, and the spatial relationship between these anomalies, the Bouguer gravity anomaly, and the Moho suggests that low-density material at the base of the crust is responsible for both the seismic and gravity signatures. We interpret this material to constitute a relict ridge subducting below the Kyushu Mountains.

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“…The northwestern end of the plateau is currently subducting beneath the Ryukyu (Nansei-Shoto) Trench (Nishizawa et al 2009). Igneous rocks obtained from the plateau suggest that its pedestal is Cretaceous in age, and the ridge portion situated on the pedestal formed in the Middle Eocene (Tokuyama et al 1986;Ishizuka and Yuasa 2007).…”

Section: Introductionmentioning

confidence: 99%

Wide-angle refraction experiments in the Daito Ridges region at the northwestern end of the Philippine Sea plate

et al. 2014

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Three large bathymetric highs (from north to south: the Amami Plateau, the Daito Ridge, and the Oki-Daito Ridge) originating from paleo-island arcs characterize the northwestern end of the Philippine Sea plate. We obtained 10 seismic refraction and multi-channel seismic reflection profiles across and along these bathymetric highs and obtained P wave velocity (Vp) models of the crust and the uppermost mantle. Although there are large variations in the crustal structure throughout this region, these bathymetric highs usually have a middle crust with Vp of 6.3 to 6.8 km/s, a lower crust with Vp of 6.8 to 7.2 km/s, a Pn velocity of 7.6 to 7.8 km/s, and a total crustal thickness of 15 to 25 km. These features are similar to those of the Izu-Ogasawara (Bonin)-Mariana island arc and the Kyushu-Palau Ridge, which are immature paleo-island arcs. However, the crust at the southwestern part of the Oki-Daito Ridge contains a relatively thin middle crust and a smaller total crustal thickness compared with other ridges in this region. In addition, we identified a deep reflector beneath the ridge, with these properties indicating a different origin, such as intraplate volcanism.

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Seismic structure of the northern end of the Ryukyu Trench subduction zone, southeast of Kyushu, Japan

Cited by 27 publications

References 9 publications

Variations in seismic velocity distribution along the Ryukyu (Nansei-Shoto) Trench subduction zone at the northwestern end of the Philippine Sea plate

Variations in seismic velocity distribution along the Ryukyu (Nansei-Shoto) Trench subduction zone at the northwestern end of the Philippine Sea plate

Velocity structure in the crust beneath the Kyushu area

Wide-angle refraction experiments in the Daito Ridges region at the northwestern end of the Philippine Sea plate

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