Volcanic Eruptions as a Possible Indicator of the Crustal Strain

Abstract

Time-space relation between major eruptions in Izu region and large earthquakes along the Sagami Trough shows the following correlation :
T= 49.88-21.04 logD,
where T is the time interval from beginning of a major eruption to the occurrence of the large earthquake in year and D is the distance in km from the epicenter to the volcano. The relationship reveals that the time interval is shorter as the distance between the epicenter and the volcano is smaller. This suggests that a future shock area gives a stress increase to the volcano and a major eruption occurs by squeezing up of magma. Then, it would be followed by a large earthquake along the Sagami Trough to release a compressional strain accumulation. Subsequently, the magma reservoir is expanded and the magma head subsides down, and a series of the volcanic activities ceases. This change is closely related to a level change of the magma head in the summit crater of Izu-Oshima Volcano. Thereby, Izu-Oshima Volcano has a role as a very sensitive strain gauge. The time-space relationship suggests that the strain in the region along the middle Sagami Trough has been accumulated since the major eruption of Izu-Oshima Volcano in 1986.