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-P12] ICDP DSeis 9: are streaks in the M5.5 aftershocks potentially located on highly stressed intrusive?

*Ryogo Tadokoro1Katsuya Ishibashi2Horiuchi Shigeki3Hiroshi Ogasawara4 (1.Graduate School of Science and Engineering, Ritsumeikan Univ.、2.School of Science and Engineering, Ritsumeikan Univ.、3.Homeseismo ltd.、4.College of Science and Engineering, Ritsumeikan Univ.)

ICDP drilling into the aftershock zone of the 2014 M5.5 earthquake near Orkney, South Africa commenced on 2017 and was completed in 2018. 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. 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.



In order to discuss further, we relocated aftershocks with the Double-Difference method (Waldhouser and Ellsworth, 2004). At the moment, we could relocate only 60 events at the upper fringe of the aftershocks. We used in-mine seismic network data of Anglogold Ashanti. P- and S- arrival times that the algorithm of Horiuchi et al. (2011) was used. A sharper alignment of aftershocks is successfully illustrated. By JpGU 2019, we will make additional efforts to extend the area of relocation to discuss more.


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.