September 13th, 1953, nearly 42 tons of explosives were detonated at Kamaisi Mine, Iwate Prefecture in the northeastern part of Japan. Location of the explosion was almost the same as the first explosion in the Kamaisi Mine of 1952. Observations of seismic waves generated by the explosion were made at fifteen temporary stations set up in the north-south directions.
Special care was teken for time keeping, and some improvements were made in the instruments.
The results of the observations are interpreted as follows:
(1) No surface layer is found. (very thin if any)
(2) From an analysis of P wave velocity, a layer of 6.05km/sec with a thickness of 22.2km or 25.6km overlies the second layer of 7.27km/sec or 7.55km/sec.
(3) From an analysis of S wave velocity, a layer of 3.46km/sec with a thickness of 32.4km. or 35.8km overlies the second layer of 4.57km/sec or 4.75km/sec.
(4) From an analysis of reflected waves, the thickness of the layer of 6.05km/sec. is 22.13km.
The uncertainty of the velocity in the first layer and an existence of Pn layer of 8.2km/sec will be studied more closely in the next opportunity.
Remark: The interpretation is based on the present observations alone, and other series of observations in the same region are entirely neglected. Therefore the present paper shows only apparent features. A general analysis on all available data has been oraly presented and will be published in the near future.
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