根尾断層周辺に発生する極微小地震の観測
1965 年 18 巻 2 号 p. 103-112
詳細
1965 年 18 巻 2 号 p. 103-112
On August 1963, the observations of ultra microearthquakes were carried out by the Research Group for Ultra Microearthquakes. One of the main purposes of these observations was to elucidate the seismic activity of microearthquakes occurring in Chubu and Kinki Districts, especially in the vicinity of Neo Valley Fault in Central Honshu, Japan. Most of these observations were made by use of velocity seismographs with high magnification (about 106-107mm/kine at short period less than 1sec.) in order to register very small earthquakes of seismic magnitudes less than zero and to get a good noise-to-signal ratio at the short period.
During the observation period, about 1, 500 earthquakes were observed by our Group at temporary stations, 9 in total, and also at 4 routine stations of Kyoto and Gifu Universities, spread widely over Kinki and Chubu Districts up to distance of about 170km. As the result of the observations, we could find that about 50 earthquakes, including microearthquakes of M less than 2 or 3, were occurring every day in this region. This fact showss that the seismicity of a given region of high activity can be estimated from high-gain recordings during a very short time interval.
