表面波の分散から見た地殻-マントル構造に関する最近の二, 三の話題
1964 年 73 巻 3 号 p. 172-180
詳細
1964 年 73 巻 3 号 p. 172-180
A few regions for which special crust-mantle system has to be suggested from the observation of surface wave dispersion are given.
1. Group velocity of Rayleigh waves which travelled along East-Pacific Rise shows the maximum value as low as 3.90 km/sec for such a short period as around 25 second. This result indicates the mantle with low shear wave velocity in its upper part overlain by a relatively thin crust. Group velocity dispersion curve of Rayleigh waves along Mid-Atlantic Ridge also shows the similar structure beneath the ridge.
2. Lateral inhomogeneity just below Moho-discontinuity has been discussed from the observation of body waves. Phase velocity dispersion of Rayleigh waves due to a nuclear explosion test has also revealed lateral variation of elastic properties of materials below Moho in Nevada district.
3. Mantle Rayleigh waves passing through the western side of Andesite - line in the western Pacific Ocean show the dispersion character remarkably different from that through other Pacific area. This fact suggests a special upper mantle situation beneath the region in question.
