SIGNIFICANT ERUPTIVE ACTIVITIES RELATED TO LARGE INTERPLATE EARTHQUAKES IN THE NORTHWESTERN PACIFIC MARGIN

Abstract

Definite spatial and temporal relations were found between large interplate earthquakes and eruptive activities along the arc systems in the northwestern Pacific margin; Kurile-Kamchatka and Japan areas. A major pattern of the relation between both phenomena reveals that eruptive activity increases during the preseismic stage to the landward of the rupture zone in the direction parallel to the convergent plate motion. Increased eruptive activity had occurred from between 2 to 27 years prior to the large earthquakes. The volcanoes usually cease their activities and sometimes decrease them after seismicity. The intense activity generally migrates to adjacent areas, namely to the landward extension of seismicity gaps. These observations suggest that the eruptive activity is strongly influenced by regional tectonic stresses, and that the accumulated crustal strain may squeeze up magmas. Support for this conclusion was obtained by observing the level change of the magma head at Mihara-yama in Oshima Volcano, Japan. Some of the volcanoes also erupted immediately after the large earthquakes. One explanation for the post-shock eruption may be provided by considering the possible effect of seismic shocks on the catastrophic seismic events. This study may provide an important key for predicting large interplate earthquakes and major eruptions in the arc areas.