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一般研究成果リスト

Detail of Grant Awarded General Researches

Project

Features of Geological Terrain Heritage of Tama River Basin expressed by Tint Sketch Method and Public Relations-Does Tachikawa Fault really exists?-

General
Research
No.222
Principal
Investigator
Akemi Nojiri
Affiliation
(at that time)
( スケッチ地盤工学者 )
Research
Summary

Tama district, where Philippine Sea and Pacific Ocean Plates are sinking, consists of complicated rock formations, valleys, caves and faults like mosaic. And furthermore Kanto Roam layer deposited all over Tama River basin, which is composed of falling ashes from Mt. Fuji, gives this district more specific geotechnical environment.


The author, a geotechnical engineer, who knows well the features of the history and the strata of this district, has conducted a site survey by visual observation all over the area of so claimed “Tachikawa active fault” district by some seismologists, making tint sketches of landscapes.


 “Tachikawa Fault” is now claimed to be the cause of huge epicentral earthquake by some pedantic leading seismologists. Their model is composed of only one big crack with approx. 10km depth and about 10km length. They also claim that if this crack breaks again a huge earthquake of seismic intensity 7 and magnitude 7.4 will occur.


Although it is unnatural that an once broken crack will break again, the strata in Japan, so called Sand-pile archipelago should contain uncountable cracks (not one).  The author has investigated the site to find out evidences that “Tachikawa Fault” really exists, making tint sketches of this area.


As a result of comparative analysis with other data of national research projects led by mainly seismologists, no evidence for existence of Tachikawa Fault has been found. The cliff lines that they claim the signs of the fault are located lower land only.  Furthermore as they are the disturbances of very shallow ground, they are supposed to be river terraces of ancient Tama River. Therefore no evidence of “Tachikawa active fault” can be found and the author concluded no active fault that will generate earthquake exists. 


The author is now making researches for another faults in Tama River basin with the same method, such as extended Itukaich fault, Itukaichi-kawakami techtonic line.


  The author is summarizing these results into booklets and distributing them to related local governments and striving educational activities for local residents through lectures and symposiums.


 These activities will reduce the unnecessary cost for research and mitigation measures and the cost already spent is said to be more than 1 trillion yen for 40 years.


In the near future, extended Itukaichi fault and Itukaichi-kawakami techtonic line and other faults may be claimed as active dangerous faults by seismologists. The author believes that this research result will be useful tool for related people. 


Collaborators
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