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The two facts gave impact to the tsunami research. One is the reliability of tide records and the other is necessity of the dispersion terms that are neglected in the analysis of near-field tsunamis regarded as a matter of course. Tide gauges are designed to cut such short period oscillation as wind waves, the wave height of which is much bigger than that of tide.
To avoid this disturbance, installed is a hydraulic filter consisted of a narrow and long conduit pipe. This hydraulic filter also acted to reduce much the tsunami records of near-shore origin. Satake et al. Fortunately, in the case of the Chilean Tsunami, this hydraulic filter was not effective due to the long wave period of the far-field tsunami. The tide gage records of the Japan Sea Earthquake Tsunami solid line and the corrected waveforms for the tide gage response dotted line From Satake et al. Another impact was the generation and development of a train of short waves at the tsunami front.
The wave period of each wave is nearly 10 seconds, similar to wind waves. In the linear long wave theory and the shallow-water equations used in the tsunami numerical simulation, the vertical acceleration of water particle is assumed to be negligible. Iwase et al. Shigihara and Fujima showed the characteristics of several schemes theoretically and recommended an implicit scheme to solve the dispersive long wave equations without any instability.
At night on July 12th, , an earthquake off west coast of Hokkaido generated a tsunami. The southernmost area of Okushiri Island was completely devastated by the tsunami, even though the area was protected by seawalls constructed after the Japan Sea Earthquake Tsunami. The crown height of seawalls was 4.
This fact called for serious reflection to the conventional method after that relied mainly on structures. The first is the selection of the design tsunami. One candidate is the largest past tsunami from which credible materials can be obtained, and another is the possible tsunamis caused by the largest earthquake that can be supposed to occur based on present knowledge and science. After comparing both tsunamis, one with the higher water level on coast is selected as the standard tsunami to ensure safety insofar as possible.
The second is the combination of three components; defense structure, tsunami-resistant town development and evacuation based on warning, in an improved and revised form of those proposed by CEDP 1 in The highest run-up was found at the bottom of a narrow valley on the west coast of Okushiri Island.
At the entrance of the valley 50 m wide, the tsunami trace height was about 22 m, and the maximum run-up 31 m high was marked at a horizontal distance 50 m from the entrance. In this case, it is obvious that the assumption of long waves is no longer valid. If applied to the case of Okushiri Island, the two-dimensional simulation outside the valley is continued to the three-dimensional simulation in the valley in the neighborhood of the valley entrance.
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The method of Fujima et al. In order to make coastal residents recognize the tsunami risk, a useful means is tsunami hazard maps for the past tsunamis and the possible tsunamis in future. After the s, many local governments have been publishing tsunami hazard maps, prepared with the numerical methods described above. Cabinet Office et al.
Earthquake a surprise
Katada et al. One of quite powerful means in public education is three-dimensional CG animations.
Many coastal residents who know a huge tsunami in the past only as a tale become to recognize the natural threat and prepare for it at their own initiative. A rough estimate of damage caused by the past tsunamis was given in terms of tsunami intensity. For example, damage to houses is caused not only by tsunami force but also by impact of drifted lumbers and boats. Matsutomi obtained a formula to evaluate the impact of lumbers as a result of large scale experiments. After the Indian Ocean Tsunami, many examples were collected for coastal forests that might damp the tsunami power.
In case of Japan, limit and effectiveness of pine forests is given. Large scale hydraulic experiments are being carried out in many institutes and laboratories. Arikawa et al. Nishihata et al. After the s, investigation on tsunami deposit was started. With geological data, we can know events in prehistoric age. Sawai et al. The biggest problem we have to solve in the near future is the detailed profile of a tsunami when it is born. When seismological data were not available, the inversion propagation method was used to determine the source area and rough estimate of the distribution of vertical displacement.
For example, see Hatori. The highest vertical rise was 1. Initial tsunami profiles obtained by Tanaka et al. When the Mansinha-Smylie is used, it is assumed that the fault motion is homogeneous in a fault plane. Satake introduced an inversion method to estimate heterogeneous fault motion, by using tide records. For the further development, inevitable is the accumulation of tsunami records near the tsunami source. The Tokachi-Oki Earthquake Tsunami was recorded by a tsunami gauge of pressure type just in the source area, as the first case of the tsunami birth.
On November 5th, , an earthquake occurred off Kii Peninsula. A tsunami was generated and recorded on a GPS tsunami gauge installed at the water depth of m, 23 km offshore. The computed tsunami with the initial profile estimated by the Mansinha-Smylie method agreed very well with the recorded. So many vivid videos and data were taken in Indian Ocean Tsunami. Those gave tsunami researchers various suggestions. However, the researchers who are going to use data of Indian Ocean Tsunami often face difficulties. Because some videos recorded the local event occurred nearby video-men, and those do not give a total information of the tsunami.
In addition, there are some areas where accurate chart and map are not available. Among recent tsunamis, the Japan Sea Earthquake Tsunami is the treasure house of actual faces of tsunami. In the event, several tsunami features were looked down from hills and airplanes, and they were recorded in videos and photos. The latter was used as the data for an international bench mark test, in which many modelers competed to show the superiority of their numerical model.
In order to support such competition, there is other necessary condition, that is, good charts and good maps are extremely important. Both are often lacked in many developing countries.
Japan Earthquake & Tsunami of Facts and Information | Live Science
However, in Japan, the Hydrographic Department of the Japan Coast Guard completed detailed bathymetric maps after the event. Accurate land maps are available from the Geographic Survey Institute. Tsunami research has been developing in Japan, because the country suffers tsunami disaster frequently in comparison with other countries.
That is why the tsunami research is of great importance in Japan. Basic materials such as bathymetric charts for the research easily obtained, and the seed and hint of the research can be found in well-filed documents and records. National Center for Biotechnology Information , U. Find articles by Nobuo Shuto.
Find articles by Koji Fujima. Author information Article notes Copyright and License information Disclaimer. Communicated by Kiyoshi H orikawa , m. Received May 29; Accepted Jul This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
This article has been cited by other articles in PMC. Abstract The tsunami science and engineering began in Japan, the country the most frequently hit by local and distant tsunamis. Keywords: hazard mitigation, numerical simulation, coastal dikes, comprehensive counter-measures.
Introduction The Sumatra Earthquake and Indian Ocean Tsunami gave us a vivid description of menace of major tsunamis.
2018 Indonesia quakes and tsunamis: Facts, FAQs, and how to help
Age of the empirical total tsunami-mitigation from to In the early morning on March 3rd, , 37 years after the Meiji event, another major tsunami struck the Sanriku Region. Tsunami control forests: Vegetations may damp the power of tsunamis. Seawalls: These could be effective for smaller tsunamis.