11:45 〜 12:00
[SVC38-16] 2017年の南岳爆発に前後する傾斜ひずみ変化
キーワード：桜島火山、南岳爆発、地盤変動、傾斜ひずみ
A deformation source associated with each eruption at Sakurajima have been estimated beneath Minami-dake [Ishihara, 1990; Iguchi et al., 2013]. Deformation sources for mid-long-term magma intrusion event were estimated beneath Aira caldera, Kita-dake and Minami-dake; and the deformation source beneath Kita-dake was found to act as a buffer of mid-long eruptive activity at Sakurajima [Hotta et al., 2016].
On November 13, 2017, an explosion with an infrasound occurred at Minami-dake at 22:07. Ground deformation was accompanied and kept for approximately five hours. For the period of 22:07–22:10 (period I), a large strain change at Arimura observation tunnel, which is the nearest tilt/strain station from Minami-dake crater and operated by Ministry of Land Infrastructure, Transport and Tourism, was detected whereas no significant change in tilt/strain was detected at other tilt/strain stations. For the period of 22:10–22:50 (period II), tilt/strain change was detected at all tilt/strain stations associated with violent eruptive activity. At around 23:00, style of eruption shifted from Vulcanian to Strombolian. For the period of 22:50–3:00 of the next day (period III), a pattern of tilt change at Japan Meteoritical Agency (JMA)-A station, which located on western area of Sakurajima, and tilt/strain gradually stopped.
We modeled the detected tilt/strain change using a finite spherical source model [McTigue, 1987]. Because of the poor constraint of the radius of the source, we assumed the radius of the source as 20 m for period I and 200 m for periods II and III. A shallow deflation source was located at a depth of 0.1 km above sea level beneath Minami-dake for period I. A deeper deflation source was located at a depth of 5.9 km below sea level beneath Minami-dake for period II. Then, a deflation source was located at a depth of 5.9 km below sea level beneath Kita-dake for period III. Deformation sources beneath Minami-dake for periods I and II are corresponding to the deformation sources previously found for each eruption at Sakurajima. Meanwhile, the deformation source beneath Kita-dake for period III is corresponding to the deformation source beneath Kita-dake which was found during mid-long eruptive activity. Each eruption at Sakurajima revealed to cause deflation of not only Minami-dake source but also Kita-dake one, which considered to repeat inflation/deflation during mid-long eruptive activity at Sakurajima. Temporal development of deflation accompanied by the eruption on November 13, 2017, will be revealed in our future study.
On November 13, 2017, an explosion with an infrasound occurred at Minami-dake at 22:07. Ground deformation was accompanied and kept for approximately five hours. For the period of 22:07–22:10 (period I), a large strain change at Arimura observation tunnel, which is the nearest tilt/strain station from Minami-dake crater and operated by Ministry of Land Infrastructure, Transport and Tourism, was detected whereas no significant change in tilt/strain was detected at other tilt/strain stations. For the period of 22:10–22:50 (period II), tilt/strain change was detected at all tilt/strain stations associated with violent eruptive activity. At around 23:00, style of eruption shifted from Vulcanian to Strombolian. For the period of 22:50–3:00 of the next day (period III), a pattern of tilt change at Japan Meteoritical Agency (JMA)-A station, which located on western area of Sakurajima, and tilt/strain gradually stopped.
We modeled the detected tilt/strain change using a finite spherical source model [McTigue, 1987]. Because of the poor constraint of the radius of the source, we assumed the radius of the source as 20 m for period I and 200 m for periods II and III. A shallow deflation source was located at a depth of 0.1 km above sea level beneath Minami-dake for period I. A deeper deflation source was located at a depth of 5.9 km below sea level beneath Minami-dake for period II. Then, a deflation source was located at a depth of 5.9 km below sea level beneath Kita-dake for period III. Deformation sources beneath Minami-dake for periods I and II are corresponding to the deformation sources previously found for each eruption at Sakurajima. Meanwhile, the deformation source beneath Kita-dake for period III is corresponding to the deformation source beneath Kita-dake which was found during mid-long eruptive activity. Each eruption at Sakurajima revealed to cause deflation of not only Minami-dake source but also Kita-dake one, which considered to repeat inflation/deflation during mid-long eruptive activity at Sakurajima. Temporal development of deflation accompanied by the eruption on November 13, 2017, will be revealed in our future study.