Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Evening Poster

S (Solid Earth Sciences) » S-VC Volcanology

[S-VC43] Volcanic and igneous activities, and these long-term forecasting

Sun. May 20, 2018 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall7, Makuhari Messe)

convener:Teruki Oikawa(GSJ, National Institute of Advanced Industrial Science and Technology), Takeshi Hasegawa(Department of Earth Sciences, College of Science, Ibaraki University), Daisuke MIURA(一般財団法人 電力中央研究所 地球工学研究所 地圏科学領域, 共同), Nobuo Geshi(Geological Survey of Japan, The National Institute of Advanced Industrial Science and Technology)

[SVC43-P11] Repeat observations of the total magnetic intensity in 2014-2017, at Zao volcano

*Toshiki Kaida1, Masahiro Ichiki1, Tomotsugu Demachi1, Satoshi Hirahara1, Takashi Nakayama1, Makiko Sato1, Ryusuke Yamamoto1, Mare Yamamoto1, Satoshi Miura1, Sendai Regional Headquarters, Japan Meteorological Agency 2 (1.Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate school of Science, Tohoku Univercity, 2.Sendai Regional Headquarters, Japan Meteorological Agency)

Keywords:Zao volcano, repeat observation of the total magnetic intensity

Zao volcano lies on the border between Yamagata and Miyagi prefectures. After the 2011 off the Pacific coast of Tohoku Earthquake, deep low frequency earthquakes have increased below 20 km depth beneath Zao since 2012. Volcanic tremors and very long-period earthquakes have been observed since 2013. To monitor subsurface geothermal activity beneath Zao volcano, we have been repeating the total magnetic intensity observation once a year since 2014. This study presents the total magnetic intensity variation from 2014 to 2017, and analyzes the demagnetized region using the 4 years’ variation.
The 14 benchmarks are settled in 2 x 2 km2 area around the crater lake, Okama, for the repeating observation. Each observation acquires total magnetic intensity during 2 minutes with 10 second sampling at 1.88 or 2.00 m height from the ground. So far, the observation was carried out on June 20, October 16, 2014, August 6, 2015, August 4, 2016 and June 20, 2017. To eliminate external magnetic field variations, reference geomagnetic field variations were recorded at about 5.3 km away to the east from Okama. As a result, the spatial distribution of total magnetic intensity variation represents demagnetized substratum between 2014 and 2017. The maximum amplitude of the variation in 4 years is about 6 nT.
Using the total magnetic intensity variation data, we model a demagnetized region with grid search. Here we assume demagnetized region to be ellipsoidal shape and 5 A/m demagnetization. The grid search seeks the location, axes’ length, and attitude of ellipsoid. Ichiki et al. (2016) modeled a demagnetized ellipsoid using the 4 month total magnetic intensity variation data in 2014. The center located at 700 m NE from the center of Okama, and 350 m depth, the long, middle, and short axis length is 500, 475, and 190 m, and strike, plunge and yaw angle is almost EW, 0 and 0, respectively. The grid search is going on in this study, and we will present the result, resolution of model and discussion of implication for future eruption.

For this study, we have used the computer systems of the Earthquake and Volcano Information Center of the Earthquake Research Institute, the University of Tokyo.