日本地球惑星科学連合2018年大会

講演情報

[EJ] ポスター発表

セッション記号 S (固体地球科学) » S-CG 固体地球科学複合領域・一般

[S-CG57] 変動帯ダイナミクス

2018年5月23日(水) 15:30 〜 17:00 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:深畑 幸俊(京都大学防災研究所)、竹下 徹(北海道大学大学院理学院自然史科学専攻)、岩森 光(海洋研究開発機構・地球内部物質循環研究分野)

[SCG57-P18] Characteristics of the seismic gap in west part of the central Kyushu, Japan

*湯浅 雄平1松本 聡2中尾 茂3松島 健2大倉 敬宏4 (1.九州大学大学院理学府地球惑星科学専攻、2.九州大学大学院理学研究院附属地震火山観測研究センター、3.鹿児島大学大学院理工学研究科地球環境科学専攻、4.京都大学大学院理学研究科附属地球熱学研究施設火山研究センター)

The seismicity in Amakusa islands located at west part of Kyushu Island, Japan is much lower than other part of Kyushu. Investigating characteristics of the seismicity gap is important for knowing the mechanism of earthquake generation. Here, we conducted analyses to consider cause of the gap and effect on the surrounding area.
In this study, we considered three models to explain the low seismicity. (1) high strength model: elastic property is much higher than the surrounding area. (2) weak zone model: no brittle failure occur in the area because of weak strength, and (3) low shear loading model: weakening shear stress loaded to the region due to inelastic deformation in the surrounding area. For verifying reliability of models (1) and (2), we considered an infinite elastic plate with a circular inclusion having different elastic constants from surrounding infinite plate. And then, we compared the spatial pattern of strain based on two dimensional theoretical equation by Nishimura and Sezawa (1931) with that of observed strain rate obtained from the GNSS network. For model (3), we calculated the distribution of the inelastic strain rate due to the earthquakes using the method of Kostrov (1974). The results reveals that the crustal deformation around Amakusa islands can not be explained by the models (1) and (2). Therefore it seems the model (3) is presumable because the region with the high inelastic strain rate(~10-8 /yr ) is seen to surrounding Amakusa islands. However, we need to revise the model (3) by taking into account the estimated stress field, velocity structure, and viscous structure in the Kyushu obtained by previous study.