表面波位相速度法により求めた日本の地殻構造
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概要
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Three earthquakes in the last six years produced satisfactory records of Rayleigh waves, with periods of 20 to 40 seconds, at about 40 stations in Japan operated by the Japan Meteorological Agency. One of these earthquakes was the Samoa shock of April 14, 1957. Epicentral distance of this earthquake from Japan along a path was about 70° and the waves approached Japan along a path perpendicular to the trend of the island arc (Aki, 1960). Another was the Aleutian shock of March 9, 1957. Epicentral distance was about 35° and the waves approached Japan along a path parallel to the trend of the islands (Kaminuma and Aki, 1963). The other was the Mindanao shock of September 24, 1957. Epicentral distance was about 33° and the direction of wave approach from this shock was nearly the reverse of that from the Aleutian shock (Kaminuma, 1964).<BR>Phase velocities for different regions in Japan were determined by the method of least squares applied to the arrival times of selected wave peaks at several stations within each region.<BR>In determing the crustal thickness from the phase velocity, we used the phase velocity curves of Aki's model 6EJ. This model modified Press' model 6EG in such a way that the velocities were uniformly reduced by 5.5 %.<BR>The crustal thickness of each region determined by using the three earthquakes are compatible within a limit of probable errors in most regions. But in the Chubu region, the phase velocity of Rayleigh waves propagated parallel to the trend of Japanese Islands is 4 % greater than that for the perpendicular path.<BR>A map of crustal thickness in Japan is drawn by using the phase velocity data of Rayleigh waves from the Samoa, Aleutian and Mindanao shocks as shown in Fig. 5.
- 社団法人 東京地学協会の論文