The third observation of ultra microearthquakes were carried out by the Research Group of Ultra Microearthquakes from August 10th to August 25th 1965, in the vicinity of Wakayama.
The purposes of the observation are 1) to learn the precious seismicity of ultra microearthquakes in the seismic region, 2) to find the reliability of the observation method and estimate the approximate structure of the crust in this region.
Seven of the observations were small aperture seismometer array stations and the others were single seismometer site observation stations. Authors had charge the arrangement of the result obtained by these array stations, and found the accuracy of the apparent velocity of
P waves and the azimuth determined by each temporary seven stations. Accuracy of hypocenter location also has been verified by the comparison of the result obtained by three methods (i. e.,
S-P times, arrival time, and tripartite method) independently, but we could not estimate the certain structure of the crust in this region.
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