Investigations into earth's crustal structure from the observations of seismic surface waves since 1955 were reviewed. In this first paper, the results of estimation concerning the oceanic crustal structure are given.
1. Pacific Ocean : Dispersions of Rayleigh waves due to both natural shocks and nuclear explosions have been observed along as many as more than 300 different paths. Rather continental crustal structure in the western side of Andesite line is quite clear from the dispersion of Rayleigh waves. Interesting fact is the abnormal dispersion character of Rayleigh waves along the paths through the East Pacific Rise. General crustal view in the whole Pacific basin has been given.
2. Atlantic Ocean : Noticeable fact is that dispersion of Rayleigh waves along the Mid-Atlantic Ridge has the same character as that along the East Pacific Rise.
3. Arctic Ocean : It has been revealed from the observation of both Lg waves and dispersion of Rayleigh waves that area of oceanic basin is rather small.
4. Indian Ocean : Investigations of crustal structure in this Ocean is still scanty.
5. From the observation of Lg waves, Bearing Sea and central Part of Japan Sea have both been concluded to have oceanic crusts. Most part of Okhotsk Sea, however, looks like to have continental crustal structure.
6. Many observational results have revealed the continental crustal structures in East China Sea and Yellow Sea basins.
7. The thickness of the sedimentary layer has been estimated at some Bays.
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