日本地球惑星科学連合2019年大会

講演情報

[E] ポスター発表

セッション記号 M (領域外・複数領域) » M-IS ジョイント

[M-IS02] 地球掘削科学

2019年5月27日(月) 17:15 〜 18:30 ポスター会場 (幕張メッセ国際展示場 8ホール)

コンビーナ:山田 泰広(海洋研究開発機構 海洋掘削科学研究開発センター)、針金 由美子(産業技術総合研究所)、黒柳 あずみ(東北大学学術資源研究公開センター東北大学総合学術博物館)、山口 耕生(東邦大学, NASA Astrobiology Institute.)

[MIS02-P11] ICDP DSeis 8: the M5.5 fault structure and reflective intrusives in legacy 3D seismic reflection data

*野田 拓1Manzi Musa2Ogasawara Hiroyuki1Linzer Lindsay2Enslin Stephanie2Durrheim Ray2小笠原 宏1 (1.立命館大学、2.Witwatersrand大)

キーワード:ICDP DSeis、M5.5地震発生場、地震反射法探査

ICDP drilling into the aftershock zone of the 2014 M5.5 earthquake near Orkney, South Africa commenced on 2017 and was completed in 2018. Hiroyuki et al. (2017 AGU) reported on legacy seismic reflection to analyze geological structures in the southern most area of the M5.5 aftershock zones. They found vertical structures in four 2-D lines that were potentially responsible for the M5.5 earthquake and illustrated cross-cutting relations of the M5.5 structure and other known faults that dislocated gold reefs more than several hundreds of meters both horizontally and vertically. Another legacy seismic reflection data which was recorded in 1996 and covered much wider area of the M5.5 aftershock zone was found. We calibrated velocity structure by tying with borehole data including DSeis Holes A and B, we found some of intrusives (sills) that Hole A and B were strong reflectors in the legacy 3D seismic reflection data.

Aftershocks located by in-mine 46 geophones are dense at the southern upper fringe, with a sharp cut-off dipping about 20 degrees to the south; some clear stripes of aftershocks are also seen, in parallel to the upper fringe (Tadokoro et al., JpGU2019, ICDP DSeis 9). It is interesting to note that the reflector (sills) are also in parallel to the upper fringe of the aftershock zone and the aftershock stripes. It is also notable that stress concentration is reported at the intrusives by Sugimura et al. (JpGU2019; ICDP DSeis 5) and Kanematsu et al. (JpGU2019; ICDP DSeis 6). Some mechanism that controls the extent of the aftershocks should exist.

This paper is one of nine papers (ICDP DSeis 1-9). Refer other papers for other topics, e.g. on drilling, logging, stress measurements and evaluation, fault materials, and relocated aftershocks.

Acknowledgement: The DSeis team includes co-authors of the papers ICDP DSeis 2-9 and members shown at https://www.icdp-online.org/projects/world/africa/orkney-s-africa/details/. We thank Harmony Gold, Anglogold Ashanthi, Lesedi, Digital Surveying, OHMS, Seismogen, 3D Geoscience. ICDP, JSPS, SA NRF, MEXT Japan, US NSF, German DRF, and Ritsumeikan Univ. financially support the project.