伊豆半島における地震及び歪の観測

Abstract

The crustal activities in and around the Izu peninsula have been remarkably since 1972 off Izupeninsula earthquake. The earthquake swarms have frequently occurred northeast area of the peninsula.The crustal movement in this area has been continuously upheaved since 1975.Strain variations and seismic waves have been recorded at Kawazu and Yugashima observation stations from 1980 and 1982, respectively. During 1991 and 1992, strain and seismic sensors and recording systems at two stations were replaced by new types.This systems are introduced in this paper.Most big event was the 1986 Izu-oshima eruption.A strain meter at Yugashima showed a good correlation with the cumulative discharge of magma.Broad-band seismometers recorded many precursory phases.We found the important relation that the duration time of precursory phase is proportion to the earthquake magnitude.