地殻変動連続観測による地震予知

抄録

Continuous observations of crustal movements in tunnels, which have been carried out in various regions in Japan since 1930's, provide valuable information about the ground deformations related with earthquake occurrences. The author summarized the precursory ground strains and tilts that had been reported since the last symposium in 1972 on the earthquake prediction research in Japan. They amounted to 30 cases during the last decade. These data suggest that continuous observation of crustal movement in and near a fractured zone plays an important role for the detection of earthquake precursor. Fractured zones seem to amplify precursory phenomena. A typical example was the observation at Yasutomi station on the Yamasaki fault, known as a quaternary active fault. It was reported that anomalous slip movements in the fractured zone after rainfall were clearly observed during few days prior to the increase in the activity of microearthquakes. It has been clarified that at some observatories, a strain response to rainfall shows temporal variations which may be related to an occurrence of earthquakes around the observatories. The author has applied a tank model to simulate normal strain responses to rainfalls at the Mikawa Crustal Movement Observatory. Abnormal strain responses to rainfalls can be detected by this simulator. 24 cases of abnormal responses were recognized during the period from January, 1973 to December, 1983. It seems that underground water makes a notable contribution to such a phenomenon. The relationship between the logarithmic precursor-times and the earthquake magnitudes for the present 30 precursory data is expressed by a linear function. The precursor-time, for a large shock, obtained by a least squares fitting is shorter than that of Rikitake's one.