Structure of the tsunamigenic plate boundary and low-frequency earthquakes in the southern Ryukyu Trench

Arai, Ryuta; Takahashi, Tsutomu; Kodaira, Shuichi; Kaiho, Yuka; Nakanishi, Ayako; Fujie, Gou; Nakamura, Yasuyuki; Yamamoto, Yojiro; Ishihara, Yasushi; Miura, Seiichi; Kaneda, Yasufumi

doi:10.1038/ncomms12255

Cited by 50 publications

(77 citation statements)

References 36 publications

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“…In contrast, clear slant reflectors can be traced to a depth of ~25 km, as shown by arrows in the MCS record, and these reflection signals have a negative polarity, indicating an abrupt decrease in velocity at the reflector. Arai et al (2016) observed similar reflection signals in the vicinity of ECr5, and they suggested the reflector is a possible tsunamigenic fault of the 1771 Meiwa Tsunami (Yaeyama Earthquake: M~8). However, there is no significant deformation at the seafloor.…”

Section: Subduction Of the Philippine Sea Platementioning

confidence: 52%

“…This indicates high pore pressure at the subduction interface in the deeper part and weak interplate coupling in the Ryukyu Trench subduction zone, as Arai et al (2016) suggested. In contrast, Goto (2013) suggested strong plate coupling caused the 1911 Kikai-jima Earthquake in the northern Ryukyu Trench.…”

Section: Subduction Of the Philippine Sea Platementioning

confidence: 64%

“…We need more information about this region to discuss this issue. Arai et al (2016) pointed out the relationship between the V p structure and short-term slow slip events (SSE) estimated by Nishimura (2014). However, we cannot discuss such a relationship through the Ryukyu subduction zone because the positions of our survey lines did not correspond to the SSE source area except for ECr10 (Fig.…”

Section: Subduction Of the Philippine Sea Platementioning

confidence: 99%

“…For instance, Hsu et al (2013) discussed the mega-splay fault system detected by an MCS survey and tsunamigenic faults such as the 1771 Meiwa Tsunami, while Arai et al (2016) investigated the fault structure and seismic activity on the basis of passive and active observations in the southern Ryukyu Trench. However, it is difficult to conduct such extensive seismic surveys over the entire Ryukyu Trench region since the trench is very long, about 1400 km, and is far from Honshu, the main island of Japan.…”

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 Platementioning

confidence: 52%

Section: Subduction Of the Philippine Sea Platementioning

confidence: 64%

Section: Subduction Of the Philippine Sea Platementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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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“…Low-frequency earthquakes (LFEs), which are categorized as seismically slow earthquakes with dominant frequencies of several Hertz, have been observed by ocean-bottom seismometers in the southern Ryukyu Trench (Arai et al 2016). For example, a swarm of LFEs was detected at the depth of 15-25 km in the southern Ryukyu Trench.…”

Section: Introductionmentioning

confidence: 99%

Distribution of low-frequency earthquakes accompanying the very low frequency earthquakes along the Ryukyu Trench

Nakamura

2017

Earth Planets Space

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This study investigated the activity and distribution of low-frequency earthquakes (LFEs) accompanying the very low frequency earthquakes (VLFEs) in the central and southern Ryukyu Trench. This investigation was based on shortperiod seismometer waveforms obtained by the Japan Meteorological Agency from April 2004 to December 2015. The LFEs were detected using the Envelope Correlation Method, and the hypocenter locations were established using the arrival time difference of the envelope. The arrival times of the P-and S-phases were selected for events in which conspicuous P and S arrivals were observed and their hypocenters were determined. The results showed that LFEs are distributed 30-50 km from the trench axis in the Okinawa and Yaeyama areas. These areas correspond to a slab depth of 12-25 km. The LFEs and VLFEs occurred in association with slow slip events (SSEs) in the Okinawa and Yaeyama areas, indicating that they are induced by SSEs in the Ryukyu Trench. Moreover, the SSEs, LFE-VLFEs, and thrust-type ordinary earthquakes exhibit separate distributions. This suggests change in the frictional condition at the slab depth of 12-25 km along the trench axis in the Ryukyu subduction zone. In the southern Ryukyu Trench, LFEs occur approximately 50 km from the SSE faults, suggesting that SSEs trigger the LFEs near the southern Ryukyu Trench.

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Crustal structure of the southern Okinawa Trough: Symmetrical rifting, submarine volcano, and potential mantle accretion in the continental back‐arc basin

et al. 2017

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Back‐arc basins are a primary target to understand lithospheric evolution in extension associated with plate subduction. Most of the currently active back‐arc basins formed in intraoceanic settings and host well‐developed spreading centers where seafloor spreading has occurred. However, rift structure at its initial stage, a key to understand how the continental lithosphere starts to break in a magma‐rich back‐arc setting, is poorly documented. Here we present seismological evidence for structure of the southern Okinawa Trough, an active rift zone behind the Ryukyu subduction zone. We find that the southern Okinawa Trough exhibits an almost symmetric rift system across the rift axis (Yaeyama Rift) and that the sedimentary layers are highly cut by inward dipping normal faults. The rift structure also accompanies a narrow (2–7 km wide) on‐axis intrusion resulted from passive upwelling of magma. On the other hand, an active submarine volcano is located ~10 km away from the rift axis. The P wave velocity (Vp) model derived from seismic refraction data suggests that the crust has been significantly thinned from the original ~25 km thick arc crust and the thinnest part with 12 km thickness occurs directly beneath the rift axis. The velocity model also reveals that there exists a thick layer with Vp of 6.5–7.2 km/s at lower crustal levels and may indicate that mantle materials accreted at the bottom of the crust during the crustal stretching. The abrupt crustal thinning and the velocity‐depth profile suggest that the southern Okinawa Trough is at a transitional stage from continental rifting to seafloor spreading.

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Structure of the tsunamigenic plate boundary and low-frequency earthquakes in the southern Ryukyu Trench

Cited by 50 publications

References 36 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

Distribution of low-frequency earthquakes accompanying the very low frequency earthquakes along the Ryukyu Trench

Crustal structure of the southern Okinawa Trough: Symmetrical rifting, submarine volcano, and potential mantle accretion in the continental back‐arc basin

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