Estimation of surface displacement around Kuju volcano before and after the 2016 Kumamoto earthquake using ALOS-2 data

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  • Mimura Yusuke
    Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University
  • Ishitsuka Kazuya
    Department of Urban Management, Graduate School of Engineering, Kyoto University
  • Oda Yoshiya
    Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University
  • Kubota Kenji
    Civil Engineering Research Laboratory, Central Research Institute of Electric Power Industry

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  • ALOS-2データを用いた2016年熊本地震前後の九重山の地表変動の推定
  • ALOS-2 データ オ モチイタ 2016ネン クマモト ジシン ゼンゴ ノ ココノエサン ノ チヒョウ ヘンドウ ノ スイテイ

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Abstract

<p>Kuju volcano comprises a series of volcanic mountains located in Oita prefecture. Mt. Iwo lies in Kuju volcano, where a phreatic eruption occurred in 1995, and still continues to eject smoke and ash. The 2016 Kumamoto earthquake occurred on April 16, 2016 and its aftershocks distributed around Kuju volcano. The 2016 Kumamoto earthquake could influence on the activity of Kuju volcano. In this study, therefore, in order to monitor the recent surface displacement of Kuju volcano, we applied SAR interferometry and SAR interferometry time-series analysis (SBAS analysis). For the analysis, we used 17 scenes of ALOS-2 data acquired between August 28, 2014 and November 14, 2016.</p><p>As the analysis results during the period of the data used in this study, significant surface displacements were not found around Kuju volcano except Mt. Iwo. Before the 2016 Kumamoto earthquake (August 18, 2014 - February 25, 2016), ground subsidence was observed at Mt. Iwo. Then, a large-scale uplift of about 4 cm were observed immediately after the earthquake (April 18, 2016 - June 13, 2016). After that (from June 13, 2016), ground subsidence was observed again at the same subsidence rate as before the earthquake. These results suggest that the influence of the 2016 Kumamoto earthquake would be temporary, and there was no clear change of trend of surface displacement in the long-term perspective.</p><p>Furthermore, in order to estimate the mechanism and the source depth of the surface displacement of Mt. Iwo, we employed analytical deformation models of the crust. As a result, we found that the depth of the pressure source both before and after the 2016 Kumamoto earthquake corresponds to the depth of the steam pool (at the depth of 0.4 km). On the other hand, we estimated that the surface displacement immediately after the 2016 Kumamoto earthquake have a pressure source located deeper than the fluctuation before and after the earthquake.</p>

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