2020 Volume 73 Pages 227-235
The first geophysical exploration by the Japanese scientist is a gravity survey conducted by Motonori Matsuyama at the Faculty of Science in Kyoto Imperial University in 1915 on the Jalute Atoll in the Marshall Islands using the Eötvös’s gravity-variometer. The purpose of this survey is to estimate the depth of bedrock below the coral reef. In order to minimize the effect of temperature change, the measurements could be begun after sunset under the best conditions before morning. As the results, the probable depth of the bed rock was 243 m for rock density of 2.6 g/cm3, and 466m for rock density of 3.0 g/cm3. The first geophysical exploration conducted in Japan is the magnetic survey by Gaichi Yamada at the Faculty of Engineering in Kyoto Imperial University in 1919 at the Takano mine in Hyogo Prefecture, using the Thalēn-Tiberg magnetometer. As the survey results, the clear magnetic anomalies are obtained near the outcrop. The first electrical prospecting in Japan is the self-potential method conducted by Fumio Oda at the Faculty of Engineering in Kyushu Imperial University in 1924. However, the author could not find the paper that described the detail of the survey. The first electrical prospecting published as a paper is the self-potential method carried out in 1925 by Yoshikata Fujita at the Faculty of Engineering in Kyoto Imperial University using the Schlumberger’s apparatus at the Yanahara mine in Okayama prefecture. As the result, the equipotential line having a clear negative potential center near the left bank of Yoshii River is obtained. The first seismic survey is a refraction survey conducted by Seizo Haeno at the Faculty of Science in Tokyo Imperial University in 1931 to determine the thickness of the riverbed gravel layer at the planned site for the construction of a hydroelectric power plant dam in Yamagata prefecture. A radio seismometer developed by Haeno was used. As the results, it is obtained that the thickness of the gravel layer is 5.5 m to 6.3 m.
The calculation program which can do the numerical simulation of seismic waves first created in Japan is a Days-2 Code which is made by the author. The Honshu-Shikoku Bridge Authority has planned the world's first method of submarine blasting with no free surface. Therefore, a numerical simulation was conducted using the Days-2 Code in 1974 to predict all phenomena generated by this special blasting. Honshu-Shikoku Bridge Authority conducted a test blasting of this method in 1975. The actual measurement results of the ground vibration generated by the test blasting were compared with the prediction results by the numerical simulation, and it was confirmed that the both were coincide quite well. In addition, the maximum ground vibration measured was about 7 times larger than the value calculated using the blast vibration estimation formula conventionally used. From this, the effectiveness of the numerical simulation by the Days-2 Code was confirmed.
