日本地球惑星科学連合2018年大会

講演情報

[EJ] Evening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) 17:15 〜 18:30 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-P21] Precise hypocenters determined by the "0.1 Manten" hyper dense seismic network: Implication of faulting structure linked to geological observation

★Invited Papers

*加藤 愛太郎1松本 聡2飯尾 能久3酒井 慎一10.1満点 稠密地震観測グループ (1.東京大学地震研究所、2.九州大学、3.京都大学防災研究所)

To deepen fundamental understanding of earthquake faulting, it is of crucial importance to image fine scale structure of fault zone. We have installed a thousand of seismic stations in the source area, which covers an entire aftershock zone of the 2000 Western-Tottori earthquake (Mw 6.7) from March 2017. The spatial interval of each seismic station ranges from 1 to 2 km. We initially detected ~3000 earthquakes from the continuous waveforms, using automatic arrival time picking technique. Applying a double-difference algorithm to the arrival data-set, we relocated more precise hypocenters in the studied region. The completeness magnitude of the catalog is around -1.0.

From the center to the southeast part, the relocated hypocenters are aligned along sharp fault planes, which are dipping almost vertically. In contrast, at the northwest area, the hypocenter distributions are complex, including several fault planes which are conjugate to the main NW-SE aftershock trend.

We focus on a tiny seismic cluster associated with Mj 1.7 event. Following this event, a total of ~150 micro-earthquakes were detected by matched filter technique. The relocated micro-earthquakes are sharply aligned along NNW-SSE fault strike. The length and dip-width of the fault dimension is about 200 m, respectively. Based on the distribution of earthquakes, the fault zone width is estimated to be at most 10 m. The ratio of the fault (process) zone width to the fault length is 0.005, which fairly matches with that geological observation of fault exposure. In addition, we find out that the tiny seismic cluster consists of several minor alignments which are oblique to the main trend, suggesting a development of Riedel shear (R) planes in the fault zone. This result indicates that this fault zone is likely at incipient stage of fault evolution.