Structural Research on the Nankai Trough Using Reflections and Refractions

To understand the megathrusut earthquake recurrence system around the Nankai trough southwestern Japan, the structural researches by seismic survey and observations will provide the significant information of megathrust earthquakes seimogenic zone. As previous structural researches, the subducting seamount in the Nankai earthquake seismogenic zone off Shikoku Island, the ridge subducting system in the Tokai earthquake seismogenic zone, splay faults in the Tonankai earthquake seismogenic zone and irregular structure in the boundary between the Tonankai and Nankai seismogenic zone off Kii peninsula.These structures and models are very important, significant and basical information to understand the recurrence system of megathrust earthquakes and rupture propagations.In this project, we will carry out seismic survey and tomography with dense arrays around the Nankai trough extending to off Hyuga sesimogenic zone. By 2004 Sumatra megathrust earthquake, we recognized such the large scale seismic linkage as 1960 Chile megathrust earthquake.Therefore, we will image large detailed large scale structures to understand structural components around the Nankai trough with off Hyuga area. Finally, we will construct the advanced structure model and develop the crustal medium model in close cooperation with other structural researches in this project. Based on these models, simulation and disaster mitigation researches will progress conspicuously.

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Western Nankai Trough seismogenic zone: Results from a wide-angle ocean bottom seismic survey

Journal of Geophysical Research Atmospheres ◽

10.1029/1999jb900394 ◽

2000 ◽

Vol 105 (B3) ◽

pp. 5887-5905 ◽

Cited By ~ 80

Author(s):

Shuichi Kodaira ◽

Narumi Takahashi ◽

Jin-Oh Park ◽

Kimihiro Mochizuki ◽

Masanao Shinohara ◽

...

Keyword(s):

Nankai Trough ◽

Seismic Survey ◽

Seismogenic Zone ◽

Ocean Bottom ◽

Wide Angle

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Special Issue on Resilience Science and Resilience Engineering to Enhance Resilience in Shikoku Region of Japan

Journal of Disaster Research ◽

10.20965/jdr.2017.p0711 ◽

2017 ◽

Vol 12 (4) ◽

pp. 711-711

Author(s):

Yoshiyuki Kaneda ◽

Chikako Isouchi

Keyword(s):

Nankai Trough ◽

Individual Characteristics ◽

Mitigation Strategies ◽

Disaster Mitigation ◽

Special Issue ◽

Megathrust Earthquake ◽

Kobe Earthquake ◽

Research And Education ◽

The Individual ◽

Resilience Science

Japan has one of the highest levels of seismicity in the world. In the last few decades, Japan has been the site of many destructive earthquakes, such as the 1995 Kobe earthquake, 2003 Tokachi-oki earthquake, 2004 Chuetsu earthquake, 2007 Chuetsu-oki earthquake, and 2016 Kumamoto earthquake/Tottori-chubu earthquakes. Furthermore, we need to take disaster mitigation countermeasures in preparation for the next Nankai Trough megathrust earthquake, Tokyo earthquake, etc. Disaster countermeasures against these earthquakes will be of vital importance to Japanese society in the future. As a specific example, if and when the next Nankai Trough megathrust earthquake strikes, it will cause widespread and compound disasters on the island of Shikoku and in southwestern Japan in general. The prefectures of Kagawa, Tokushima, Kochi, and Ehime are all on the island of Shikoku, yet the damages that a future Nankai Trough megathrust earthquake will cause are predicted to be quite different in each prefecture. Therefore, in preparing disaster mitigation strategies for the coming Nankai Trough megathrust earthquake, these four prefectures and the distinguished universities involved in disaster mitigation research and education in them must be united in collaboration while making the best use of the individual characteristics of the prefectures and universities. Specifically, in terms of disaster mitigation preparations, universities on Shikoku have to develop and advance resilience science as it relates to upcoming disasters from a Nankai Trough megathrust earthquake, inland earthquakes, typhoons, floods, etc. In this special issue, many significant research papers from the fields of engineering, geoscience, and the social sciences by researchers from distinguished universities on the island of Shikoku focus on resilience science. We must apply their findings to society, putting them into practice to mitigate potential damages from any future natural events.

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

Volume 5: Ocean Space Utilization; Ocean Renewable Energy ◽

10.1115/omae2011-50090 ◽

2011 ◽

Cited By ~ 2

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.

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Structural factors controlling the rupture process of a megathrust earthquake at the Nankai trough seismogenic zone

Geophysical Journal International ◽

10.1046/j.1365-246x.2002.01691.x ◽

2002 ◽

Vol 149 (3) ◽

pp. 815-835 ◽

Cited By ~ 108

Author(s):

S. Kodaira ◽

E. Kurashimo ◽

J.-O. Park ◽

N. Takahashi ◽

A. Nakanishi ◽

...

Keyword(s):

Nankai Trough ◽

Rupture Process ◽

Seismogenic Zone ◽

Structural Factors ◽

Megathrust Earthquake

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Long‐Period Ground Motions from Past and Virtual Megathrust Earthquakes along the Nankai Trough, Japan

Bulletin of the Seismological Society of America ◽

10.1785/0120180320 ◽

2019 ◽

Vol 109 (4) ◽

pp. 1312-1330

Author(s):

Loïc Viens ◽

Marine A. Denolle

Keyword(s):

Subduction Zone ◽

Large Scale ◽

Nankai Trough ◽

Ground Motions ◽

Accretionary Wedge ◽

Impulse Response Functions ◽

Ocean Bottom ◽

Ocean Bottom Seismometer ◽

Megathrust Earthquakes ◽

Long Period

Abstract Long‐period ground motions from large (Mw≥7.0) subduction‐zone earthquakes are a real threat for large‐scale human‐made structures. The Nankai subduction zone, Japan, is expected to host a major megathrust earthquake in the near future and has therefore been instrumented with offshore and onshore permanent seismic networks. We use the ambient seismic field continuously recorded at these stations to simulate the long‐period (4–10 s) ground motions from past and future potential offshore earthquakes. First, we compute impulse response functions (IRFs) between an ocean‐bottom seismometer of the Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET) network, which is located offshore on the accretionary wedge, and 60 onshore Hi‐net stations using seismic interferometry by deconvolution. As this technique only preserves the relative amplitude information of the IRFs, we use a moderate Mw 5.5 event to calibrate the amplitudes to absolute levels. After calibration, the IRFs are used together with a uniform stress‐drop source model to simulate the long‐period ground motions of the 2004 Mw 7.2 intraplate earthquake. For both events, the residuals of the 5% damped spectral acceleration (SA) computed from the horizontal and vertical components of the observed and simulated waveforms exhibit almost no bias and acceptable uncertainties. We also compare the observed SA values of the Mw 7.2 event to those from the subduction‐zone BC Hydro ground‐motion model (GMM) and find that our simulations perform better than the model. Finally, we simulate the long‐period ground motions of a hypothetical Mw 8.0 subduction earthquake that could occur along the Nankai trough. For this event, our simulations generally exhibit stronger long‐period ground motions than those predicted by the BC Hydro GMM. This study suggests that the ambient seismic field recorded by the ever‐increasing number of ocean‐bottom seismometers can be used to simulate the long‐period ground motions from large megathrust earthquakes.

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Newly Proposed Disaster Mitigation and Recovery for the Next Nankai Trough Megathrust Earthquakes

Journal of Disaster Research ◽

10.20965/jdr.2009.p0151 ◽

2009 ◽

Vol 4 (2) ◽

pp. 151-152 ◽

Cited By ~ 2

Author(s):

Yoshiyuki Kaneda ◽

◽

Michihiro Ohori ◽

Takeshi Nakamura

Keyword(s):

Working Group ◽

Nankai Trough ◽

Disaster Mitigation ◽

Mitigation Measures ◽

Group Discussions ◽

Megathrust Earthquakes ◽

Long Period ◽

Public Corporations ◽

Working Groups ◽

Integrate Research

To integrate research results of this project and apply to practical disaster mitigation measures, we arrange and construct working groups in Nagoya city, Osaka city and Kochi city. In these cities, severe damages of next megathrust earthquakes around the Nankai trough are estimated, therefore, we will discuss with administrative organs, public corporations of life lines and researchers etc. in each working group. In discussions of working group, we introduce advanced researches to understand the present and future expected researches of the Nankai trough in each other. Furthermore, we will extract characteristic issues and estimated damages of strong motions, long period motions and tsunamis based on the future scenarios of next meagthrust earthquakes in each working group. And fruits of working group discussions will contribute to constructions of new disaster mitigation measures in administrative organs, public corporations of life lines etc.

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Investigating seismic segmentation and recurrence patterns of great earthquakes along the Chilean megathrust.

10.5194/egusphere-egu2020-12150 ◽

2020 ◽

Author(s):

Diego Molina ◽

Andres Tassara ◽

Jean-Paul Ampuero ◽

Daniel Melnick

Keyword(s):

Subduction Zones ◽

Large Scale ◽

Seismogenic Zone ◽

Recurrence Time ◽

Small Scale ◽

Apparent Difference ◽

Coseismic Slip ◽

First Order ◽

Megathrust Earthquakes ◽

Chilean Margin

Megathrust earthquakes at subduction zones are one of the most devastating natural phenomena. Understanding the relationships between their temporal recurrence, spatial segmentation and the frictional structure of the megathrust is of primary relevance. We analyzed the common spatial variability of gravity anomalies, geodetic locking and wedge taper basal friction (three independent proxies for megathrust frictional structure) along the Chilean margin. A marked along-strike segmentation has emerged that is organized into three hierarchical levels. At a subcontinental-scale (103 km), we observe a first-order difference between Central (18-32&#176;S) and Southern (32&#176;-46&#176;S) Andes. This is marked by a dominance of positive/negative gravity, high/low locking, high/low friction along the Central/Southern segments. We explain this as mainly reflecting the combined effect on effective normal stress (&#963;eff) of a high/low density forearc and low/high pore pressure along both megathrust segments, in agreement with the geological structure of the forearc, sediment input at the trench and the long-term architecture of the Andes. Inside this large-scale subdivision, we identify a number of segments (102 km) that are limited by marked small-scale (101 km) changes in the first-order tendency of the three proxies coinciding with geological features of both plates. When we compare this against the paleoseismic, historic and instrumental record of past earthquakes in Chile, we note that segments largely coincide with seismic asperities, i.e. those regions of the megathrust concentrating the largest fraction of coseismic slip. Bridging these two scales, the rupture length of giant (Mw 8.5-9.5) earthquakes, which encompassed several asperities, define an intermediate hierarchic level of organization (102-103 km). Considering this segmentation into the conceptual framework of the rate-and-state friction (RSF) law, we infer that asperities inside the rate-weakening seismogenic zone of the Central Andean megathrust are dominantly unstable (i.e. &#963;eff>&#963;c = the critical stress defined by RSF parameters) and therefore prone to initiate and concentrate the coseismic rupture. In contrast, most of the asperities along the Southern mega-segment are likely characterized by a conditionally-stable behavior (&#963;eff<&#963;c) that allows a rich and complex seismogenic behavior where interseismic creep and locking are both possible and large coseismic slip propagation is dominant. This can explain the apparent difference in the recurrence of giant earthquakes along both mega-segments, since the synchronization of unstable asperities in the Central Andean megathrust (2000-3000 yr recurrence time) is less probable than in the case of conditionally-stable asperities in the Southern segment (300-500 yrs). We will test these hypothesis developing numerical simulations of multiple seismic cycles with setups representing the inferred contrast on the physical properties of the megathrust along the Chilean margin, and we will present preliminary results of this exercise.&#160;

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