伊豆大島で観測される地電位差異常変動の原因についての一考察

Abstract

Uyeda et al., reported that the anomalous changes of the telluric potential observed at Izu-Oshima island using the telegraphic facilities are possibly precursors of earthquake swarms off the east coast of Izu Peninsula. The fact, however, that almost all their ‘signals’ appear from 6 to 22 o'clock implies that those ‘signals’ are of man-made origin. On the basis of the evidences, the author claims that those anomalous changes are not related with earthquakes but are caused by the leak current associated both with the use of the telephone and the precipitation. The ‘fact’ on which their conclusion was based that the number of occurrence of the anomalous changes of the telluric potential a day increases before the commencement of the earthquake swarms is not actual. Furthermore, the fact that we had big earthquake swarms off the east coast of the Izu Peninsula once a year in the rainy season in these three years might have lead them to the fault. Their observational results simply reveal that the noise level of the self-potential at Izu-Oshima Island rose due to the precipitation, as we often usually experience.