POSSIBLE CORRELATION BETWEEN GEOELECTRIC POTENTIAL CHANGE IN IZU-OSHIMA ISLAND AND THE EARTHQUAKE SWARM OFF THE EAST IZU PENINSULA, JAPAN

Since May, 1987, we have monitored the geoelectric potential change in Izu-Oshima Island using three long-span dipoles and NTT (Nippon Telegraph and Telephone corporation) facilities. Occasionally anomalous potential changes, which were different from those induced by geomagnetic variations, have been observed. Their possible correlation with nearby seismic activity has been examined, with the result that the daily number of appearances of one type of anomalous potential change increased shortly before M > 5 events in all three earthquake swarms that have occurred since 1987 in the area off the east Izu Peninsula. Whether or not this correlation is valid and useful for prediction purpose is still not certain.