ANOMALOUS SEISMIC ACTIVITY AND EARTHQUAKE PREDICTION

Abstract

The earthquake off the Izu Peninsula, on May 9, 1974 (M=6.9) was preceded by an anomalous seismic activity which started about 10 years and 4 months before, in July 1963 and can be distinguished from the ordinary seismic activity in the region. This earthquake was not, however, preceded by immediate foreshocks. At the same time there seems to have been some changes in seismic wave velocities in the above region. Similar phenomena were also found for 10 earthquakes which occurred at shallow depths in Japan. The relation between earthquake magnitude M and the precursor time T in days taken from the above data is given by logT=0.77M-1.65. The relation between earthquake magnitude and precursor time found for other phenomena such as velocity of seismic waves, electric resistivity, crustal deformation, radon concentration in the ground water, etc., is given by respective investigators. These relations as well as my formula are examined. These results seem to suggest that among the above-mentioned precursory phenomena the seismic anomalous activity is the first one to take place. This may be due to the beginning of the formation of many ruptures in the region where the strain energy has been sufficiently stored.