scholarly journals Crustal deformation detection capability of the GNSS-A seafloor geodetic observation array (SGO-A), provided by Japan Coast Guard

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Yusuke Yokota ◽  
Tadashi Ishikawa ◽  
Shun-ichi Watanabe ◽  
Yuto Nakamura
Keyword(s):  
Standard Deviation ◽  
Crustal Deformation ◽  
Deformation Rate ◽  
Nankai Trough ◽  
Coast Guard ◽  
Detection Capability ◽  
Positioning Accuracy ◽  
Transient Event ◽  
Seafloor Geodetic Observation ◽  
Slip Event

AbstractThe GNSS-A technique is an observation method that can detect seafloor crustal deformations with centimeter-level positioning accuracy. The GNSS-A seafloor geodetic observation array operated by the Japan Coast Guard (SGO-A) has been constructed near the Japanese Islands along the Nankai Trough and the Japan Trench. This observation array has detected several earthquakes’ displacements and episodic slow crustal deformation. To compare the detection results of SGO-A with other observation networks and expand the SGO-A coverage area, it is necessary to correctly understand its detection capability. In this paper, numerical simulations and statistical verifications were used to assess the capabilities of the present GNSS-A system using a manned vessel (observation frequency: 4–6 times/year, positioning accuracy: standard deviation = 1.5 cm) to detect (1) secular deformation only, (2) a transient slip event only and (3) secular deformation and a transient event together. We verified these results with appropriate thresholds and found the following features: When it is known that there is no transient event, the 95% confidence level (CL) for the estimation of secular crustal deformation rate with 4-year observation is about 0.5–0.8 cm/year; when the deformation rate is known, a signal of about 3.0 cm can be detected by observations of about 4 times before and after the transient event. When the deformation rate and the transient event are detected together, to keep the false positive low (about 0.05), the false negative becomes high (about 0.7–0.2 for detecting a signal of 4.5–6.0 cm). The determined rate and event variations are approximately 1.8 cm/year (95%CL) and 1.5 cm (standard deviation), respectively. We also examined the detection capability for higher observation frequency and positioning accuracy, to examine how the detection capability improves by technological advancements in the future. Additionally, we calculated the spatial range of event detectability using the determined values of detection sensitivity. Obtained results show that each seafloor site can detect a slip event of < 1.0 m scale within about 30 km radius, and approximately one-third of the subseafloor slip event over 100 km from land along the Nankai Trough can only be detected by SGO-A.

scholarly journals Crustal Deformation Detection Capability Associated With a Fault Slip on the Interplate Boundary in the Gnss-a Seafloor Geodetic Observation Array (SGO-A), Provided By Japan Coast Guard

2021 ◽  
Author(s):  
Yusuke Yokota ◽  
Tadashi Ishikawa ◽  
Sun-ichi Watanabe ◽  
Yuto Nakamura
Keyword(s):  
Standard Deviation ◽  
Crustal Deformation ◽  
Deformation Rate ◽  
Coast Guard ◽  
Detection Sensitivity ◽  
Japan Trench ◽  
Detection Capability ◽  
Geodetic Observation ◽  
Seafloor Geodetic Observation ◽  
Slip Event

Abstract The GNSS-A technique is an observation method that can detect seafloor crustal deformations with centimeter level accuracy. The GNSS-A seafloor geodetic observation array operated by the Japan Coast Guard, called SGO-A, has been constructed near the Japan Islands along the Nankai Trough and the Japan Trench. This observation array has detected several earthquakes’ displacements and episodic slow crustal deformation. To compare the detection results of SGO-A with other observation networks and expand the SGO-A distribution, it is necessary to correctly understand its detection capability. In this paper, the capabilities of current GNSS-A (frequency: f = 4–6 times/year, position accuracy: σ (standard deviation) = 1.5 cm) to detect a crustal deformation rate only, an event only, and crustal deformation rate and event together were arranged by numerical simulations. Results suggested the following features: when it is known that there is no event, the 95% confidence level (CL) for the estimation of crustal deformation rate with 4-year observation is about 0.5–0.8 cm/year; when the deformation rate is known, a signal of about 3.0 cm can be detected by observations of about 4 times before and after the event. When the deformation rate and the event are detected together, to keep the false positive low (about 0.05), the false negative becomes high (about 0.2–0.7 for detecting a signal of 4.5–6.0 cm). The determined rate and event variations are approximately 1.8 cm/year (95%CL) and 1.5 cm (standard deviation), respectively. We also examined the detection capability for higher frequency and accuracy, to examine how the detection capability improves by technological advancements in the future. Additionally, we calculated the spatial range of event detectability using the determined values of detection sensitivity. Each seafloor site can detect a slip event larger than 0.1 m scale within about 50 km radius. A subseafloor slip event smaller than about 1 m at the distance of 100 km or more from the land can often be detected only on the seafloor observation array.

scholarly journals Precise Monitoring of Pore Pressure at Boreholes Around Nankai Trough Toward Early Detecting Crustal Deformation

2021 ◽  
Vol 9 ◽  
Author(s):  
Keisuke Ariyoshi ◽  
Toshinori Kimura ◽  
Yasumasa Miyazawa ◽  
Sergey Varlamov ◽  
Takeshi Iinuma ◽  
...  
Keyword(s):  
Normal Stress ◽  
Pore Pressure ◽  
Crustal Deformation ◽  
Nankai Trough ◽  
Time Lag ◽  
Pressure Change ◽  
Ocean Modeling ◽  
Effective Normal Stress ◽  
Seafloor Pressure ◽  
The Impact

In our recent study, we detected the pore pressure change due to the slow slip event (SSE) in March 2020 at the two borehole stations (C0002 and C0010), where the other borehole (C0006) close to the Nankai Trough seems not because of instrumental drift for the reference pressure on the seafloor to remove non-crustal deformation such as tidal and oceanic fluctuations. To overcome this problem, we use the seafloor pressure gauges of cabled network Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET) stations nearby boreholes instead of the reference by introducing time lag between them. We confirm that the time lag is explained from superposition of theoretical tide modes. By applying this method to the pore pressure during the SSE, we find pore pressure change at C0006 about 0.6 hPa. We also investigate the impact of seafloor pressure due to ocean fluctuation on the basis of ocean modeling, which suggests that the decrease of effective normal stress from the onset to the termination of the SSE is explained by Kuroshio meander and may promote updip slip migration, and that the increase of effective normal stress for the short-term ocean fluctuation may terminate the SSE as observed in the Hikurangi subduction zone.

scholarly journals Heterogeneous interplate coupling along the Nankai Trough, Japan, detected by GPS-acoustic seafloor geodetic observation

2015 ◽  
Vol 2 (1) ◽  
Author(s):  
Yusuke Yokota ◽  
Tadashi Ishikawa ◽  
Mariko Sato ◽  
Shun-ichi Watanabe ◽  
Hiroaki Saito ◽  
...  
Keyword(s):  
Nankai Trough ◽  
Geodetic Observation ◽  
Seafloor Geodetic Observation ◽  
Interplate Coupling

scholarly journals Characteristics of Slow Slip Event in March 2020 Revealed From Borehole and DONET Observatories

2021 ◽  
Vol 8 ◽  
Author(s):  
Keisuke Ariyoshi ◽  
Takeshi Iinuma ◽  
Masaru Nakano ◽  
Toshinori Kimura ◽  
Eiichiro Araki ◽  
...  
Keyword(s):  
Pore Pressure ◽  
Crustal Deformation ◽  
Nankai Trough ◽  
Pressure Sensors ◽  
Plate Boundary ◽  
Volumetric Strain ◽  
Time History ◽  
Pressure Change ◽  
Plate Interface ◽  
Deformation Component

We have detected an event of pore pressure change (hereafter, we refer it to “pore pressure event”) from borehole stations in real time in March 2020, owing to the network developed by connecting three borehole stations to the Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET) observatories near the Nankai Trough. During the pore pressure event, shallow very low-frequency events (sVLFEs) were also detected from the broadband seismometers of DONET, which suggests that the sVLFE migrated toward updip region along the subduction plate boundary. Since one of the pore pressure sensors have been suffered from unrecognized noise after the replacement of sensors due to the connecting operation, we assume four cases for crustal deformation component of the pore pressure change. Comparing the four possible cases for crustal deformation component of the volumetric strain change at C0010 with the observed sVLFE migration and the characteristic of previous SSEs, we conclude that the pore pressure event can be explained from SSE migration toward the updip region which triggered sVLFE in the passage. This feature is similar to the previous SSE in 2015 and could be distinguished from the unrecognized noise on the basis of t-test. Our new finding is that the SSE in 2020 did not reach very shallow part of the plate interface because the pore pressure changes at a borehole station installed in 2018 close to the trough axis was not significant. In the present study, we estimated the amount, onset and termination time of the pore pressure change for the SSE in 2020 by fitting regression lines for the time history. Since the change amount and duration time were smaller and shorter than the SSE in 2015, respectively, we also conclude that the SSE in 2020 had smaller magnitude that the SSE in 2015. These results would give us a clue to monitor crustal deformation along the Nankai Trough directly from other seafloor observations.

scholarly journals Onshore-offshore seismic transect from the eastern Nankai Trough to central Japan crossing a zone of the Tokai slow slip event

2005 ◽  
Vol 57 (10) ◽  
pp. 943-959 ◽  
Author(s):  
Shuichi Kodaira ◽  
Takashi Iidaka ◽  
Ayako Nakanishi ◽  
Jin-Oh Park ◽  
Takaya Iwasaki ◽  
...  
Keyword(s):  
Nankai Trough ◽  
Slow Slip ◽  
Central Japan ◽  
Slow Slip Event ◽  
Slip Event

The ‘Horwitz ratio’—a study of the ratio between reproducibility and repeatability precisions in the analysis of foodstuffs

2015 ◽  
Vol 7 (1) ◽  
pp. 375-379 ◽  
Author(s):  
Michael Thompson ◽  
Roger Wood
Keyword(s):  
Standard Deviation ◽  
Detection Capability ◽  
Reproducibility Standard Deviation ◽  
Repeatability Standard Deviation

In the analysis of food, the ratio of reproducibility standard deviation to repeatability standard deviation is usually close to 2.0. This has implications in estimating uncertainty and detection capability.

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