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

Nishizawa, Azusa; Kaneda, Kentaro; Katagiri, Yasutaka; Oikawa, Mitsuhiro

doi:10.1186/1880-5981-66-25

Cited by 30 publications

(41 citation statements)

References 22 publications

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Section: Subduction Of the Philippine Sea Platesupporting

confidence: 50%

“…The slightly low V p of 7.6 km/s in the uppermost mantle along the southeastern end of ECr11 is same as the upper mantle velocity beneath the Amami Plateau obtained by Nishizawa et al (2014). The Pn velocity at northern end of DAr5, to the east of ECr11, is slightly higher V p of 7.8-8.0 km/s (Nishizawa et al 2014), which indicates less influence of the Amami Plateau. In the southern seismic lines of the Ryukyu Trench, Pn velocities in the southeastern end of the ECr7 and ECr6 are 7.7-7.9 and 7.8 km/s, respectively, which are slightly smaller than ~8.0 km/s obtained in the Shikoku Basin, the backarc basin on the PHS plate to the east (Nishizawa et al 2011).…”

Section: Subduction Of the Philippine Sea Platesupporting

confidence: 50%

“…Since the maximum water depth limit for the hydrophone sensor is 6000 m, we deployed the OBSs without hydrophones at positions deeper than 6000 m. The procedures for the OBS data analysis are the same as those summarized by Nishizawa et al (2014). Constructing V p models, we used information about the shallow sedimentary structures and depths of the subducting PHS plate interface deduced from MCS survey.…”

Section: Data Acquisition and Analysesmentioning

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: 50%

Section: Subduction Of the Philippine Sea Platesupporting

confidence: 50%

Section: Data Acquisition and Analysesmentioning

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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“…1) are also originated from paleo-island arcs. Nishizawa et al (2014) showed that these bathymetric highs usually have a middle crust with a Vp of 6.3-6.8 km/s, a lower crust with Vp = 6.8-7.2 km/s, a Pn velocity of 7.6-7.8 km/s, and a crustal thickness of 15-25 km. These structures are similar to those of the IBM island arc, which are immature paleo-island arcs.…”

Section: Introductionmentioning

confidence: 99%

“…Recently, the Daito Ridges, other significant bathymetric highs characterizing the Philippine Sea plate, were comprehensively investigated geologically and geophysically under the CSS Project in Japan (e.g., Ishizuka et al 2013;Nishizawa et al 2014). Three large bathymetric highs, the Amami Plateau, the Daito Ridge, and the OkiDaito Ridge, from north to south (Fig.…”

Section: Introductionmentioning

confidence: 99%

Crust and uppermost mantle structure of the Kyushu-Palau Ridge, remnant arc on the Philippine Sea plate

2016

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We acquired 27 wide-angle seismic profiles to investigate variation in crustal structure along the Kyushu-Palau Ridge (KPR), a 2600-km-long remnant island arc in the center of the Philippine Sea plate; 26 lines were shot across the strike of the KPR at 13°-31°N, and one was shot along the northernmost KPR. The derived P-wave velocity (Vp) models show that the KPR has a crustal thickness of 8-23 km, which is thicker than the neighboring backarc basin oceanic crusts of the West Philippine Basin to the west and the Shikoku and Parece Vela Basins to the east. While the KPR crust consists mainly of lower crusts with a Vp of 6.8-7.2 km/s, the thicker crust contains a thick middle crust with Vp of 6.0-6.8 km/s. In general, the KPR crust is thicker in the north than in the south. The uppermost mantle velocities just below the KPR bathymetric highs are lower than 8.0 km/s and are commonly associated with a slightly high Vp of 7.2 km/s at the base of the crust. Large amplitude reflection signals are sometimes observed at far offsets on several lines suggesting the existence of several reflectors at depths of 23-40 km in the mantle beneath the KPR. The characteristics of these reflections are similar to these observed beneath the Izu-Ogasawara (Bonin) island arc, the tectonically conjugate arc of the KPR before backarc basin spreading. Very thin crust and high Pn velocities characterize the transition between the KPR and the eastern basins, which is probably a relic of the initial stage of the rifting. West of the KPR, the crust varies in structure from north to south as a result of the different tectonic settings in which it evolved.

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Subduction initiation at relic arcs

Leng

Gurnis

2015

Geophysical Research Letters

105

110

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Although plate tectonics is well established, how a new subduction zone initiates remains controversial. Based on plate reconstruction and recent ocean drilling within the Izu‐Bonin‐Mariana, we advance a new geodynamic model of subduction initiation (SI). We argue that the close juxtaposition of the nascent plate boundary with relic oceanic arcs is a key factor localizing initiation of this new subduction zone. The combination of thermal and compositional density contrasts between the overriding relic arc, and the adjacent old Pacific oceanic plate promoted spontaneous SI. We suggest that thermal rejuvenation of the overriding plate just before 50 Ma caused a reduction in overriding plate strength and an increase in the age contrast (hence buoyancy) between the two plates, leading to SI. The computational models map out a framework in which rejuvenated relic arcs are a favorable tectonic environment for promoting subduction initiation, while transform faults and passive margins are not.

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

Cited by 30 publications

References 22 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

Crust and uppermost mantle structure of the Kyushu-Palau Ridge, remnant arc on the Philippine Sea plate

Subduction initiation at relic arcs

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