Back‐Arc Opening in the Western End of the Okinawa Trough Revealed From GNSS/Acoustic Measurements

Chen, Horng-Yue; Ikuta, Ryoya; Lin, Cheng‐Horng; Hsu, Ya‐Ju; Kohmi, Takeru; Wang, Chau-Chang; Yu, Shui-Beih; Tu, Yoko; Tsujii, Toshiaki; Ando, Masataka

doi:10.1002/2017gl075724

Cited by 21 publications

(14 citation statements)

References 25 publications

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“…The PSP has subducted northwestward beneath the Eurasian Plate along the Ryukyu Trench in a speed of~80-90 mm/year near the Taiwan-Ryukyu junction area (Seno et al, 1993;Yu et al, 1997; Figure 1). Probably because of the collision/subduction transition, the fast retreating of the south Ryukyu Arc (Hsu, 2001), and the clockwise rotation of the south Ryukyu Arc (Chen et al, 2018;Nishimura et al, 2004), the Ryukyu arc-trench system changes its orientation near 123°E from W-E to NW-SE, parallel to the plate convergence direction ( Figure 1). The Taiwan-Ryukyu junction area is also a transition zone from the PSP collision in the west to PSP subduction in the north (Angelier, 1990;Ho, 1986;Lallemand et al, 2013;Sibuet & Hsu, 2004;Suppe, 1984;Teng, 1990).…”

Section: South Ryukyu Arc and Forearcmentioning

confidence: 99%

“…The Taiwan-Ryukyu junction area is also a transition zone from the PSP collision in the west to PSP subduction in the north (Angelier, 1990;Ho, 1986;Lallemand et al, 2013;Sibuet & Hsu, 2004;Suppe, 1984;Teng, 1990). Probably because of the collision/subduction transition, the fast retreating of the south Ryukyu Arc (Hsu, 2001), and the clockwise rotation of the south Ryukyu Arc (Chen et al, 2018;Nishimura et al, 2004), the Ryukyu arc-trench system changes its orientation near 123°E from W-E to NW-SE, parallel to the plate convergence direction ( Figure 1). Along~123°E, the Gagua Ridge is~300 km long,~30 km wide, and~4 km high above the seafloor (Font et al, 2001).…”

Section: 1029/2019gl082121mentioning

confidence: 99%

“…Moreover, some earthquakes show south-dipping normal faulting above the frontal portion of the seismogenic zone (Figure 4), which is in opposition to a depression or subsidence to the north of the proposed tear fault. The location of the updip limit generally marks the seaward aseismic sliding from the seismogenic zone (Hyndman et al, 1997) or a change from unconsolidated sediments to lithified rock (Byrne, 1998). Thus, the step-down may suggest that the seaward updip portion of the subducting sediments is "squeezed," peeled off, and partly accreted to the bottom of the forearc basin and arc (Figure 4).…”

Section: Underplatingmentioning

confidence: 99%

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Earthquake‐Related Structures Beneath the Southernmost Portion of the Ryukyu Arc and Forearc

Wang

Hsu

Yeh

2019

Geophysical Research Letters

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Moderate to large earthquakes repeatedly occur beneath the southernmost Ryukyu arc and forearc, but the seismogenic structures were poorly studied. To better understand the southernmost Ryukyu seismogenic structures, we have deployed ocean bottom seismometers to record the aftershocks of a large earthquake in 2015. As a result, several groups of aftershocks are associated with the seismogenic structures. A deep group coincides with the north‐dipping seismogenic zone that terminates near the tip of the mantle wedge beneath the Ryukyu Arc. A shallow group dips southward from the southern slope of the Ryukyu Arc to the southern end of the aftershocks; this group shows south‐dipping normal faulting character and accompanies the lower crust exhumation of Ryukyu Arc above the seismogenic zone. A plate interface step‐down beneath the seismogenic zone is inferred. A crustal underplating and exhumation around the seismogenic zone have taken place synchronously during the earthquake event.

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Section: South Ryukyu Arc and Forearcmentioning

confidence: 99%

Section: 1029/2019gl082121mentioning

confidence: 99%

Section: Underplatingmentioning

confidence: 99%

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Earthquake‐Related Structures Beneath the Southernmost Portion of the Ryukyu Arc and Forearc

Wang

Hsu

Yeh

2019

Geophysical Research Letters

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“…In Japan, an onshore continuous crustal deformation observation system using the Global Navigation Satellite System (GNSS) has been operated by the Geospatial Information Authority of Japan since 1996 (e.g., 10.1029/2018JB016159 Sagiya et al, 2000). In addition, recent campaign seafloor geodetic observations using the GNSS/Acoustic combination technique (hereinafter, GNSS/A; e.g., Fujita et al, 2006;Kido et al, 2006;Spiess et al, 1998;Tadokoro et al, 2006) has been operated in offshore regions by universities and the Japan Coast Guard (e.g., Chen et al, 2017;Tadokoro et al, 2006;Tomita et al, 2017;Yasuda et al, 2014Yasuda et al, , 2017Yokota et al, 2016). These observations can detect not only coseismic or postseismic displacements associated with earthquakes but also steady interseismic displacement.…”

Section: Introductionmentioning

confidence: 99%

Interplate Coupling Distribution Along the Nankai Trough in Southwest Japan Estimated From the Block Motion Model Based on Onshore GNSS and Seafloor GNSS/A Observations

Kimura

Itô

2019

JGR Solid Earth

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Along the Nankai Trough of southwest Japan, large‐magnitude interplate earthquakes (M > 8) have occurred repeatedly, with recurrence intervals of approximately 100 years. It is essential to estimate more precisely the spatial distribution of interplate coupling; that is, along‐strike and along‐dip heterogeneity of the coupling ratio defined as the slip deficit rate divided by the plate convergence rate, for understanding the mechanisms and/or assessing the potential of future mega interplate earthquakes in this region. Recently, the seafloor Global Navigation Satellite System‐Acoustic (GNSS/A) combination technique observation network has been extended, and we can now obtain crustal displacement fields for both onshore and offshore regions. In this study, we estimate interplate coupling distribution along the Nankai Trough using both seafloor GNSS/A and onshore GNSS data with the block motion model, minimizing the spatial variations of modeling uncertainties of coupling estimates. Seafloor GNSS/A data depict very strong coupling near the trough axis off of Tokai, as well as trough‐parallel heterogeneity in interplate coupling at the shallow plate interface. Using the block motion model confirmed that observed crustal deformation above the deep plate interface in SW Japan is dominated by rigid block motion rather than elastic response to slip deficit on the deep plate interface of the subducting Philippine Sea plate. The minimization of spatial variations for the modeling uncertainties of coupling estimates helps us to estimate the coupling distribution with nearly homogeneous uncertainties between offshore and onshore regions, which is useful for evaluation of interplate earthquakes and/or tsunamis hazards.

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“…Since the 2000s, several research groups have been working on GNSS-A observation and have obtained numerous scientific results for the area around Japan, among others. For example, interseismic seafloor crustal movements have been found to constrain the slip deficit rate along the Nankai Trough (Tadokoro et al 2012;Yokota et al 2016;Yasuda et al 2017), off the northeastern coast of Japan (Fujita et al 2006;Sato et al 2011a;Sato et al 2013), and in the Okinawa Trough (Chen et al 2017). Sato et al (2011b) and Kido et al (2011) detected coseismic displacements of the Tohoku earthquake (Mw 9.0) that reached magnitudes of more than 20 m near the Japan Trench.…”

Section: Introductionmentioning

confidence: 99%

Assessment of directional accuracy of GNSS-Acoustic measurement using a slackly moored buoy

Imano

Kido

Honsho

et al. 2019

Prog Earth Planet Sci

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We assessed the positioning accuracy of GNSS-Acoustic (GNSS-A) measurement using a slackly moored buoy. A key feature of real-time buoy-based GNSS-A measurement is that positioning must be performed via single ranging from an arbitrary observation position and encompassing the drifting range of the buoy. In this study, slack-line mooring was employed to resist strong Kuroshio current of up to 5.5 knots in the Nankai Trough. During a year-long sea trial, the buoy drifted within a circle of~4000 m radius, which is much larger than the dimension of a seafloor transponder array. In the sea trial, more than 500 successful regular and on-demand ranging measurements were obtained at various observation positions. The results show that the horizontal positioning accuracy (2σ) of the array for single ranging was 46 cm when the buoy was inside the array and 97 cm when it was outside the array. These accuracies are comparable to those achieved through single ranging in traditional ship-based surveys at the same site. In addition to the distance dependency, we observed directivity in the accuracy, depending on the geometry between an observation point and seafloor transponders. To interpret the accuracy degradation and directivity as a function of observation position, we calculated error ellipses using a dilution-of-precision (DOP) analysis procedure for GNSS-A positioning. The error ellipses clearly illustrate that the variance in array positions is large in the line-of-sight direction from an observation point to the array center. We translated the error ellipses to positioning accuracies using the standard deviation of travel time residuals when an array position is estimated using all pings. The positioning accuracy resulting from the translation corresponded to that obtained using array positions in a buoy observation. The DOP analysis results and their translation into positioning accuracies enabled a detailed assessment of the directional accuracy of GNSS-A positioning at an arbitrary observation position, which is important for realtime measurement of seafloor movement in the event of a huge earthquake.

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Back‐Arc Opening in the Western End of the Okinawa Trough Revealed From GNSS/Acoustic Measurements

Cited by 21 publications

References 25 publications

Earthquake‐Related Structures Beneath the Southernmost Portion of the Ryukyu Arc and Forearc

Earthquake‐Related Structures Beneath the Southernmost Portion of the Ryukyu Arc and Forearc

Interplate Coupling Distribution Along the Nankai Trough in Southwest Japan Estimated From the Block Motion Model Based on Onshore GNSS and Seafloor GNSS/A Observations

Assessment of directional accuracy of GNSS-Acoustic measurement using a slackly moored buoy

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