scholarly journals Mid- to late-Holocene marine inundations inferred from coastal deposits facing the Nankai Trough in Nankoku, Kochi Prefecture, southern Japan

The Holocene ◽  
2018 ◽  
Vol 28 (6) ◽  
pp. 867-878 ◽  
Author(s):  
Koichiro Tanigawa ◽  
Masanobu Shishikura ◽  
Osamu Fujiwara ◽  
Yuichi Namegaya ◽  
Dan Matsumoto
Keyword(s):  
Nankai Trough ◽  
Storm Surges ◽  
Radiocarbon Dates ◽  
Megathrust Earthquakes ◽  
Southern Japan ◽  
Lowland Area ◽  
Coastal Deposits ◽  
Sedimentary Fill ◽  
Kochi Prefecture ◽  
Sand Sheets

This study investigates the Holocene sedimentary history of a small coastal lowland in Nankoku, Kochi Prefecture, on the coast of southern Japan facing the Nankai Trough. The sedimentary fill of the lowland area consists mainly of marine-brackish clay overlain by beds of freshwater clay and peat. We found four laterally extensive sand sheets, one directly underlying the freshwater deposits and the other three interbedded with them. Radiocarbon dates show that these sand sheets were deposited between 5970 and 2440 cal. BP. Although the sand sheets contained few marine-brackish diatoms, they were concentrated in the seaward part of the study site, suggesting that they were deposited by marine inundations. These sand sheets were formed as a result of tsunamis or unusually large storm surges. The apparent frequency of marine inundations during 5970–2440 cal. BP was much lower than that of megathrust earthquakes along the Nankai Trough recorded during the last 1300 years. Event deposits were absent between 2440 and 960 cal. BP, a gap that we attribute to the development of beach ridges. The new marine inundation records reported here will aid efforts to reconstruct the timing and recurrence intervals of megathrust earthquakes in the western Nankai Trough.

Resilience Efforts in the Kochi Prefecture in Preparation for the Nankai Trough Earthquake

2017 ◽  
Vol 12 (4) ◽  
pp. 755-765
Author(s):  
Tadashi Hara ◽  
Keyword(s):  
Nankai Trough ◽  
Lessons Learned ◽  
Disaster Mitigation ◽  
Disaster Prevention ◽  
Social Infrastructure ◽  
The Pacific ◽  
Local Resilience ◽  
Kochi Prefecture ◽  
Significant Effort ◽  
Made In

For the purposes of disaster prevention and disaster mitigation against the upcoming Nankai Trough Earthquake, various efforts are being carried out. The undertaking is on the basis of lessons learned from the experience of the 2011 earthquake off the Pacific coast of Tohoku and other disasters. In the Kochi Prefecture, where serious damage is expected, significant effort is being directed towards preparing social infrastructure countermeasures for the earthquake and, particularly, the tsunami. This paper focuses on the efforts towards local resilience being made in the Kochi Prefecture and discusses new disaster-prevention countermeasures with respect to sea dikes, liquefaction, and tsunami fires.

Tsunami scenarios for megathrust earthquakes: mechanics of multi-segment ruptures and elastic-fluid dynamics of wave propagation

2020 ◽  
Author(s):  
Tatsuhiko Saito ◽  
Akemi Noda
Keyword(s):  
Fluid Dynamics ◽  
Strain Energy ◽  
Seismic Waves ◽  
Nankai Trough ◽  
Ocean Bottom ◽  
Bottom Pressure ◽  
Ocean Bottom Pressure ◽  
Megathrust Earthquakes ◽  
Great Earthquakes ◽  
Pressure Changes

<p>Great earthquakes repeatedly occurred with different rupture processes in the Nankai trough, southwestern Japan. The 1944 Tonankai and the 1946 Nankai earthquakes (M ~8) caused serious tsunami damage over many areas along the coastline. The greatest earthquake in this region is the 1707 Hoei earthquake (M 8.4) that is believed to have ruptured the whole region (~600 km) of the Nankai Trough. The purpose of this study is to theoretically assess the tsunami height along the coasts excited by great earthquakes that can possibly occur in future in this region and simulate observable tsunami records during the earthquakes.</p><p>This study employed a new method for making various rupture scenarios. Based on a shear-stress distribution along the plate boundary estimated by the GNSS data analyses (Noda et al. 2018 JGR), we calculated coseismic slip distributions to release the accumulated stress for possible multi-segment rupture scenarios. Then, we used the strain energy released by the rupture to evaluate the possibility of each event. The released strain energy should be larger than the energy dissipated on the fault. However, for some scenarios, the released strain energy was smaller than the dissipated energy under the assumptions of friction laws. Such rupture scenarios are not likely to occur in the viewpoint of earthquake mechanics. This approach can provide necessary conditions of the strain energy or the accumulated stress levels for multi-segment rupture processes, while methods based on empirical or kinematic approaches do not treat stress or interseimsmic stress-accumulation periods required for ruptures.</p><p>Another distinctive point in our approach is that we theoretically synthesize ocean-bottom pressure changes caused by both seismic waves and tsunamis using a simulation method based on elastic and fluid dynamics (Saito and Tsushima 2016 JGR; Saito et al. 2019 Tectonophysics). Seismic wave contributions to ocean-bottom pressure changes are critically important for the synthetics in near-field or inside rupture areas because the seismic waves overlap with tsunami signals and work as noise for real-time tsunami monitoring. The records simulated in this study can be used to examine the monitoring ability of a deep-ocean observation network for megathrust earthquakes and tsunamis in this region.</p>

scholarly journals Structural Research on the Nankai Trough Using Reflections and Refractions

2009 ◽  
Vol 4 (2) ◽  
pp. 67-71 ◽  
Author(s):  
Yoshiyuki Kaneda ◽  
◽  
Shuichi Kodaira
Keyword(s):  
Large Scale ◽  
Nankai Trough ◽  
Disaster Mitigation ◽  
Seismic Survey ◽  
Seismogenic Zone ◽  
Significant Information ◽  
Megathrust Earthquake ◽  
Megathrust Earthquakes ◽  
Recurrence System ◽  
Splay Faults

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.

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.

scholarly journals Impact of the Artificial Strait in the Vistula Spit on the Hydrodynamics of the Vistula Lagoon (Baltic Sea)

Water ◽  
2019 ◽  
Vol 11 (5) ◽  
pp. 990 ◽  
Author(s):  
Michał Szydłowski ◽  
Tomasz Kolerski ◽  
Piotr Zima
Keyword(s):  
Water Level ◽  
Storm Surges ◽  
High Water ◽  
Vistula Lagoon ◽  
Gulf Of Gdańsk ◽  
Sea Levels ◽  
Lowland Area ◽  
Gulf Of Gdansk ◽  
The Impact ◽  
The Vistula Lagoon

In the Vistula Lagoon, storm surges are induced by variable sea levels in the Gulf of Gdańsk and wind action. The rising of the water level in the southern part of the basin, exceeding 1.0 m above mean sea level, can be dangerous for the lowland area of Żuławy Elbląskie, causing the inundation of the polders adjacent to the lagoon. One of the potential possibilities to limit the flood risk is to decrease the water level in the lagoon during strong storm surges by opening an artificial canal to join the lagoon with the Gulf of Gdańsk. The decision to build a new strait in the Vistula Spit was made in 2017. In order to analyze the impact of the artificial connection between the sea and the lagoon during periods of high water stages in the southern part the lagoon, mathematical modelling of the hydrodynamics of the Vistula Lagoon is required. This paper presents the shallow water equations (SWEs) model adapted to simulate storm surges driven by the wind and sea tides, and the numerical results obtained for the present (without the new strait) and future (with the new strait) configuration of the Vistula Lagoon.

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