The Large-Scale Earthquake Countermeasures Act was enacted in Japan in December 1978. This act aims at mitigating earthquake hazards by designating an area to be an ‘area under intensified measures against earthquake disaster,’ such designation being based on long-term earthquake prediction information, and by issuing an ‘earthquake warnings statement’ based on imminent prediction information, when possible. In an emergency case as defined by the law, the prime minister will be empowered to take various actions which cannot be taken at ordinary times. For instance, he may ask the Self-Defense Force to come into the earthquake-threatened area before the earthquake occurrence. A Prediction Council has been formed in order to evaluate premonitory effects that might be observed over the Tokai area, which was designated an area under intensified measures against earthquake disaster some time in June 1979. An extremely dense observation network has been constructed over the area.