Interplate Coupling State at the Nansei‐Shoto (Ryukyu) Trench, Japan, Deduced From Seafloor Crustal Deformation Measurements

Nakamura, Mamoru; Ando, Masataka; Kimura, Hiroshi; Watanabe, Tsuyoshi; Matsuhiro, Kenjiro

doi:10.1029/2018gl078655

Cited by 22 publications

(22 citation statements)

References 52 publications

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“…This was done a few years later in the central Ryukyu Arc, off the Okinawa main island (Nakamura, ; Tadokoro et al, ). In this region, data from GPS/acoustic instruments revealed the existence of a strongly coupled 20‐ to 30‐km wide patch located southeast of Okinawa, with lateral extent that still remains to be accurately constrained (Tadokoro et al, ). Those results show that at least some portions of the plate interface, close to the trench, may be coupled.…”

Section: Introductionmentioning

confidence: 99%

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Relative Sea‐Level Changes Over the Past Centuries in the Central Ryukyu Arc Inferred From Coral Microatolls

et al. 2020

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This study focuses on Okinawa and Yoron islands, in order to better understand tectonics in the Ryukyu Arc related to the subduction zone. We used coral microatolls—known for their centimetric accuracy in the record of relative sea‐level (RSL) changes—to reconstruct RSL changes over the last century from living microatolls. A fossil microatoll in Yoron was used to discuss possible RSL changes beyond the last century. The signal consists of emergence whose rate varies through time, interrupted by decadal to multidecadal periods of sudden and/or gradual submergence and by interannual sea‐level falls. Comparison with other existing RSL records in the arc highlights RSL variability along the arc. This pattern contrasts with the homogeneous and linear absolute regional sea‐level rise, implying that this latter signal cannot fully explain our observations and that an additional process is required. We suggest the subduction zone as a possible source for generating centimetric scale RSL changes observed in coral microatolls. We tested how the Ryukyu megathrust could explain our observations with elastic dislocation modeling. The emergence trend could be explained by interseismic loading on the plate interface with a minimum coupling rate of 25%, which is higher than previous estimates based on short instrumental records. As for the submergence events that occurred regularly in the coral record, we show that they could be explained by slow slip events on the shallower part of the megathrust or in the transition zone. Such process could accommodate a significant part of the total convergence.

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Section: Introductionmentioning

confidence: 99%

“…The reexamination of historical records highlighted two additional historical tsunamis that occurred in 1768 and 1791 in Okinawa Island and that could have been induced by interplate M‐class 8 earthquakes on the coupled patch revealed by the offshore GPS measurements (Nakamura, ; Tadokoro et al, ).…”

Section: Introductionmentioning

confidence: 99%

Relative Sea‐Level Changes Over the Past Centuries in the Central Ryukyu Arc Inferred From Coral Microatolls

et al. 2020

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“…The Global Navigation Satellite System (GNSS)-Acoustic ranging combination technique (GNSS-A) is a unique and important technology for detecting detailed absolute seafloor crustal deformation. Many key scientific findings have been obtained with the aid of GNSS-A [2][3][4][5][6]. Our data were published in Yokota et al [7,8].…”

Section: Introductionmentioning

confidence: 81%

Gradient field of undersea sound speed structure extracted from the GNSS-A oceanography: GNSS-A as a sensor for detecting sound speed gradient

Yokota

Ishikawa

2019

SN Appl. Sci.

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“…Since an individual seafloor transponder position can be estimated using the acoustic travel-time data collected by a "moving survey" (the acoustic pings are transmitted from various sea-surface points) (e.g., Ikuta et al 2008;Honsho and Kido 2017; Additional file 1: Figure S2a), as similar to the determination of the seismological hypocenter (e.g., Hirata and Matsu'ura 1987), we can determine array geometry composed of the transponders. Then, constraining the array geometry, array displacements relative to the predetermined array position can be precisely estimated (e.g., Spiess et al 1998;Kido et al 2006;Matsumoto et al 2008;Honsho and Kido 2017;Chen et al 2018;Tadokoro et al 2018b). If the array geometry is well determined, an array displacement can be estimated using only a single acoustic ping which simultaneously transmits to all seafloor transponders (e.g., Spiess et al 1998;Kido et al 2006; Additional file 1: Figure S2b).…”

Section: Principles Of the Gnss-a Positioning Methodsmentioning

confidence: 99%

Development of a kinematic GNSS-Acoustic positioning method based on a state-space model

Tomita

Kido

Honsho

et al. 2019

Earth Planets Space

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GNSS-A (combination of Global Navigation Satellite System and Acoustic ranging) observations have provided important geophysical results, typically based on static GNSS-Acoustic positioning methods. Recently, continuous GNSS-Acoustic observations using a moored buoy have been attempted. Precise kinematic GNSS-Acoustic positioning is essential for these approaches. In this study, we developed a new kinematic GNSS-A positioning method using the extended Kalman filter (EKF). As for the observation model, parameters expressing underwater sound speed structure [nadir total delay (NTD) and underwater delay gradients] are defined in a similar manner to the satellite geodetic positioning. We then investigated the performance of the new method using both the synthetic and observational data. We also investigated the utility of a GNSS-Acoustic array geometry composed of multi-angled transponders for detection of vertical displacements. The synthetic tests successfully demonstrated that (1) the EKF-based GNSS-Acoustic positioning method can resolve the GNSS-Acoustic array displacements, as well as NTDs and underwater delay gradients, more precisely than those estimated by the conventional kinematic positioning methods and (2) precise detection of vertical displacements can be achieved using multi-angled transponders and EKF-based GNSS-Acoustic positioning. Analyses of the observational data also demonstrated superior performance of the EKF-based GNSS-Acoustic positioning method, when assuming a laterally stratified sound speed structure. Further, we found three superior aspects to the EKF-based array positioning method when using observational data: (1) robustness of the solutions when some transponders fail to respond, (2) precise detection for an abrupt vertical displacement, and (3) applicability to real-time positioning when sampling interval of the acoustic ranging is shorter than 30 min. The precision of the detection of abrupt steps, such as those caused by coseismic slips, is ~ 5 cm (1σ) using this method, an improvement on the precision of ~ 10 cm of conventional methods. Using the observational data, the underwater delay gradients and the horizontal array displacements could not be accurately solved even using the new method. This suggests that short-wavelength spatial heterogeneity exists in the actual ocean sound speed structure, which cannot be approximated using a simple horizontally graded sound speed structure.

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Interplate Coupling State at the Nansei‐Shoto (Ryukyu) Trench, Japan, Deduced From Seafloor Crustal Deformation Measurements

Cited by 22 publications

References 52 publications

Relative Sea‐Level Changes Over the Past Centuries in the Central Ryukyu Arc Inferred From Coral Microatolls

Relative Sea‐Level Changes Over the Past Centuries in the Central Ryukyu Arc Inferred From Coral Microatolls

Gradient field of undersea sound speed structure extracted from the GNSS-A oceanography: GNSS-A as a sensor for detecting sound speed gradient

Development of a kinematic GNSS-Acoustic positioning method based on a state-space model

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