Paleotsunami research along the Nankai Trough and Ryukyu Trench subduction zones – Current achievements and future challenges

2020 ◽  
Vol 210 ◽  
pp. 103333 ◽  
Author(s):  
Osamu Fujiwara ◽  
Kazuhisa Goto ◽  
Ryosuke Ando ◽  
Ed Garrett
Keyword(s):  
Subduction Zones ◽  
Nankai Trough ◽  
Ryukyu Trench ◽  
Future Challenges

Exposure of Population and Energy-Related Base Facilities to Shaking Intensity Predicted for Nankai Megathrust Earthquakes

2017 ◽  
Vol 12 (1) ◽  
pp. 106-117
Author(s):  
Nobuoto Nojima ◽  
◽  
Hiroki Kato
Keyword(s):  
Power Generation ◽  
Subduction Zones ◽  
Nankai Trough ◽  
Strong Motion ◽  
Oil Refining ◽  
Population Exposure ◽  
Oil Refineries ◽  
Megathrust Earthquakes ◽  
Fundamental Information ◽  
And Storage

The exposure of the area and population as well as energy-related base facilities to the shaking intensity predicted for the anticipated megathrust earthquakes along the Nankai Trough subduction zones is evaluated. First, area and population exposure is evaluated considering six cases of shaking intensity distribution calculated using strong motion prediction methods and an attenuation formula. Next, the exposure of energy-related base facilities is evaluated for power generation plants, oil refineries, and LNG terminals in terms of their capacities for power generation, oil refining, and storage, respectively. Exposed capacities can be evaluated approximately for arbitrary levels of shaking intensity, providing fundamental information on the potential reduction of energy supply capabilities in an earthquake disaster.

Recent advances in GNSS-A observation technology and networks and latest observation results around Japan Islands

2020 ◽  
Author(s):  
Yusuke Yokota ◽  
Tadashi Ishikawa ◽  
Shun-ichi Watanabe ◽  
Yuto Nakamura
Keyword(s):  
Subduction Zones ◽  
Large Scale ◽  
Surface Deformation ◽  
Nankai Trough ◽  
Detection Sensitivity ◽  
Japan Trench ◽  
Observation Data ◽  
Coupling Condition ◽  
Slow Slip Events ◽  
Combination Technique

<p>Our research group has been studying advanced GNSS-A (Global Navigation Satellite System – Acoustic ranging combination) technique over two decades. In recent years, detection sensitivity of GNSS-A observations has been sophisticated by improving the accuracy and frequency of analysis technology and acoustic systems [e.g., Yokota et al., 2018, MGR; Ishikawa et al., in prep]. The current observation frequency is more than 4 times/year, the observation accuracy for each observation is less than 2 cm, and it can detect a steady deformation rate of 1 cm/year or less and an unsteady fluctuation of 5 cm or less. Also, efforts are being made to strengthen the observation network.</p><p>GNSS-A observations for the 2011 Tohoku-oki earthquake and its postseismic field revealed the details of the crustal deformation field on the Japan Trench side [Sato et al., 2011, Science; Watanabe et al., 2014, GRL]. The long-term observation data in the Nankai Trough region revealed the strain accumulation process at the interseismic period [Yokota et al., 2016, Nature; Watanabe et al., 2018, JGR; Nishimura et al., 2018, Geosphere]. Furthermore, detection and monitoring of large-scale slow slip events (SSEs) in the shallow part of the Nankai Trough was achieved by recent sensitivity improvements [Yokota & Ishikawa, 2020, Science Advances]. The detected postseismic fields, coupling condition and shallow SSEs contain universal features that should be shared in many subduction zones. Here, along with the latest observations, we discuss spatial and temporal relationships of these events, strain accumulations and releases along subduction zones around Japan by GNSS-A and its impact on slow earthquake science.</p><p>Recently, because of the need for continuous monitoring a shallow SSE, the monitoring ability of GNSS-A was also investigated. It was confirmed that relatively large-scale shallow SSE (surface deformation: > 5 cm) could be monitored. However, the ability to determine the time constant of an SSE is poor. For monitoring the detail of an SSE, it is essential to improve the observation frequency in the future. Here, we also discuss the technical issues to be considered and their solution plans (e.g., new platform and system).</p>

scholarly journals Shallow slow slip events along the Nankai Trough detected by GNSS-A

2020 ◽  
Vol 6 (3) ◽  
pp. eaay5786 ◽  
Author(s):  
Yusuke Yokota ◽  
Tadashi Ishikawa
Keyword(s):  
Subduction Zones ◽  
Nankai Trough ◽  
Plate Boundary ◽  
Low Frequency ◽  
Satellite System ◽  
Boundary Region ◽  
Slow Slip ◽  
Slow Slip Events ◽  
Combination Technique ◽  
Slow Earthquakes

Various slow earthquakes (SEQs), including tremors, very low frequency events, and slow slip events (SSEs), occur along megathrust zones. In a shallow plate boundary region, although many SEQs have been observed along pan-Pacific subduction zones, SSEs with a duration on the order of a year or with a large slip have not yet been detected due to difficulty in offshore observation. We try to statistically detect transient seafloor crustal deformations from seafloor geodetic data obtained by the Global Navigation Satellite System-Acoustic (GNSS-A) combination technique, which enables monitoring the seafloor absolute position. Here, we report the first detection of signals probably caused by shallow large SSEs along the Nankai Trough and indicate the timings and approximate locations of probable SSEs. The results show the existence of large SSEs around the shallow side of strong coupling regions and indicate the spatiotemporal relationship with other SEQ activities expected in past studies.

Scientific Drilling Program of Drilling Vessel Chikyu and Drilling Data Acquisition for Future Technical Development

2011 ◽  
Author(s):  
Tomoya Inoue ◽  
Kazuyasu Wada ◽  
Eigo Miyazaki ◽  
Tsuyoshi Miyazaki
Keyword(s):  
Data Acquisition ◽  
Subduction Zones ◽  
Large Scale ◽  
Nankai Trough ◽  
Technical Development ◽  
Seismogenic Zone ◽  
Validity Data ◽  
Scientific Drilling ◽  
Drilling Data ◽  
Drilling Operations

The scientific drilling vessel Chikyu has started drilling at Nankai trough under the international organization, IODP. The Nankai trough located beneath the ocean off the southwest coast of Japan is one of the most active earthquake zones on the planet and one of the best-studied subduction zones as well. The Nankai Trough Seismogenic Zone Experiment attempts for the first time to drill, sample, and instrument the earthquake-causing or the seismogenic portion of Earth’s crust, where violent, large-scale earthquakes have occurred repeatedly throughout history. Before starting the international drilling operations, an integration drilling test off Shimokita Peninsula was conducted and we acquired actual drilling data such as vessel heave, hook load, and compensator position. Confirming its validity, data acquisition systems have worked continuously in international drilling operations. It is very important to consider the actual drilling data for the drilling operation and for further technical development. This paper describes the scientific drilling programs of the drilling vessel Chikyu and the drilling data acquisition for future technical development in relation with the sample data acquired in the internal drilling operations.

Evaluation of factors controlling smectite transformation and fluid production in subduction zones: Application to the Nankai Trough

Island Arc ◽  
2008 ◽  
Vol 17 (2) ◽  
pp. 208-230 ◽  
Author(s):  
Demian M. Saffer ◽  
Michael B. Underwood ◽  
Alexander W. McKiernan
Keyword(s):  
Subduction Zones ◽  
Nankai Trough ◽  
Fluid Production

scholarly journals Improving Detectability of Seafloor Deformation From Bottom Pressure Observations Using Numerical Ocean Models

2021 ◽  
Vol 8 ◽  
Author(s):  
Yoichiro Dobashi ◽  
Daisuke Inazu
Keyword(s):  
Atmospheric Pressure ◽  
General Circulation ◽  
Subduction Zones ◽  
Nankai Trough ◽  
General Circulation Models ◽  
Japan Trench ◽  
Observation Data ◽  
Bottom Pressure ◽  
Seafloor Deformation ◽  
Ocean Models

We investigated ocean bottom pressure (OBP) observation data at six plate subduction zones around the Pacific Ocean. The six regions included the Hikurangi Trough, the Nankai Trough, the Japan Trench, the Aleutian Trench, the Cascadia Subduction Zone, and the Chile Trench. For the sake of improving the detectability of seafloor deformation using OBP observations, we used numerical ocean models to represent realistic oceanic variations, and subtracted them from the observed OBP data. The numerical ocean models included four ocean general circulation models (OGCMs) of HYCOM, GLORYS, ECCO2, and JCOPE2M, and a single-layer ocean model (SOM). The OGCMs are mainly driven by the wind forcing. The SOM is driven by wind and/or atmospheric pressure loading. The modeled OBP was subtracted from the observed OBP data, and root-mean-square (RMS) amplitudes of the residual OBP variations at a period of 3–90 days were evaluated by the respective regions and by the respective numerical ocean models. The OGCMs and SOM driven by wind alone (SOMw) contributed to 5–27% RMS reduction in the residual OBP. When SOM driven by atmospheric pressure alone (SOMp) was added to the modeled OBP, residual RMS amplitudes were additionally reduced by 2–15%. This indicates that the atmospheric pressure is necessary to explain substantial amounts of observed OBP variations at the period. The residual RMS amplitudes were 1.0–1.7 hPa when SOMp was added. The RMS reduction was relatively effective as 16–42% at the Hikurangi Trough, the Nankai Trough, and the Japan Trench. The residual RMS amplitudes were relatively small as 1.0–1.1 hPa at the Nankai Trough and the Chile Trench. These results were discussed with previous studies that had identified slow slips using OBP observations. We discussed on further accurate OBP modeling, and on improving detectability of seafloor deformation using OBP observation arrays.

scholarly journals IODP workshop: Core-Log Seismic Investigation at Sea – Integrating legacy data to address outstanding research questions in the Nankai Trough Seismogenic Zone Experiment

2018 ◽  
Vol 24 ◽  
pp. 93-107
Author(s):  
Anna Cerchiari ◽  
Rina Fukuchi ◽  
Baiyuan Gao ◽  
Kan-Hsi Hsiung ◽  
Dominik Jaeger ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Seismic Data ◽  
Subduction Zones ◽  
Nankai Trough ◽  
Early Career ◽  
Seismogenic Zone ◽  
Geochemical Data ◽  
Deformation Front ◽  
Subduction Zone Processes ◽  
Research Questions

Abstract. The first International Ocean Discovery Program (IODP) Core-Log-Seismic Integration at Sea (CLSI@Sea) workshop, held in January–February 2018, brought together an international, multidisciplinary team of 14 early-career scientists and a group of scientific mentors specialized in subduction zone processes at the Nankai Trough, one of the Earth's most active plate-subduction zones located off the southwestern coast of Japan. The goal of the workshop was to leverage existing core, log, and seismic data previously acquired during the IODP's Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE), to address the role of the deformation front of the Nankai accretionary prism in tsunamigenic earthquakes and slow slip in the shallow portion of the subduction interface. The CLSI@Sea workshop was organized onboard the D/V Chikyu concurrently with IODP Expedition 380, allowing workshop participants to interact with expedition scientists installing a long-term borehole monitoring system (LTBMS) at a site where the workshop's research was focused. Sedimentary cores from across the deformation front were brought onboard Chikyu, where they were made available for new description, sampling, and analysis. Logging data, drilling parameters, and seismic data were also available for investigation by workshop participants, who were granted access to Chikyu laboratory facilities and software to perform analyses at sea. Multi-thematic presentations facilitated knowledge transfer between the participants across field areas, and highlighted the value of multi-disciplinary collaboration that integrates processes across different spatiotemporal scales. The workshop resulted in the synthesis of existing geophysical, geologic, and geochemical data spanning IODP Sites C0006, C0007, C0011 and C0012 in the NanTroSEIZE area, the identification of key outstanding research questions in the field of shallow subduction zone seismogenesis, and fostered collaborative and individual research plans integrating new data analysis techniques and multidisciplinary approaches.

Sign in / Sign up

Export Citation Format

Share Document