11:00 AM - 11:15 AM
[SCG62-02] Simultaneous Eruptions and Earthquakes in the 9th Century, in the East and Central Japan
Keywords:9th century , linkage of eruption and earthquake, east-west compression
Along the eastern margin of Japan Sea, the Amurian plate subducts beneath the East Japan (Okhotsk plate or North-American Plate). At the northern part of the ISTL, the East Japan thrust over Amurian plate. Along the Nankai trough, the Philippine Sea plate subducts beneath the Amurian plate. The central part of the ISTL acts as left-lateral fault to switch the direction of subuction system.
Judging from the relation between volcanic activities and 869AD Off Tohoku Jogan earthquake, 887AD Nankai trough Ninna earthquake, volcanoes did not necessarily activated by the earthquakes, but often erupt prior to great earthquakes. These examples show that it is difficult apply a simple model to the 9th century episodes that an earthquake release compressional stress and allow magma ascend.
During the recent 60 years, eruptions (Miyakejima (1962 AD, 1983AD, 2000AD), Izu-Oshima (1986 AD), Submarine eruption off Ito (1989 AD)), earthquakes along the Eastern Margin of Japan Sea (1964, 1983, 1993, 2004, 2007 AD), the Great East Japan Earthquake off Tohoku (March 11, 2011, M9.0), North Nagano earthquake (March 12, 2011 M6.7; extension of Nagano Fault System), and Kamishiro Fault Earthquake (2014AD, M6.7; occupying northern part of ISTL Active Fault System) are taking place in areas overlapping with those occurred in the 9th century.
Overflow of magma from the Miyakejima summit crater, dome formation of Niijima and Kozushima of the 9th century imply high magma head or high horizontal stress in Izu Islands. Whereas lateral eruption at Izu-Oshima in 1986 AD and the collapse of summit at Miyakejima in 2000 AD resulted from intrusions of a large amount of magma into neighboring crust indicate lower horizontal stress in recent years. Although many common points are found between 9th century and the present, the stress states are different and it is difficult to find a rule in the order among outbreak of earthquakes and eruptions.