Introduction
The Matsushiro Seismological Observatory (MAT) was established on May 1, 1947, taking advantage of the unfinished large-scale tunnel system planed and constructed by the Imperial Japanese Army. These tunnels, measuring about 3km in total length and 2.5 to 6m in diameter, locate in the depth 100m below the surface so that the internal air temperature changes little throughout the year. MAT is away from the noise sources such as railroad, automobile traffic, and the sea coast, which is at least 60km away. Those conditions were suit for the seismograph installation. (MAT is not an exception recently suffering from the artificial noises.)
