JpGU-AGU Joint Meeting 2017

Presentation information

[JJ] Oral

M (Multidisciplinary and Interdisciplinary) » M-IS Intersection

[M-IS22] [JJ] Drilling Earth Science

Wed. May 24, 2017 3:30 PM - 5:00 PM IC (International Conference Hall 2F)

convener:Yasuhiro Yamada(Japan Agency for Marine-Earth Science and Technology (JAMSTEC), R&D Center for Ocean Drilling Science (ODS)), Katsuyoshi Michibayashi(Institute of Geosciences, Shizuoka University), Minoru Ikehara(Center for Advanced Marine Core Research, Kochi University), Yusuke Suganuma(National institute of Polar Research), Chairperson:Yasuhiro Yamada(Japan Agency for Marine-Earth Science and Technology (JAMSTEC), R&D Center for Ocean Drilling Science (ODS)), Chairperson:Yusuke Suganuma(National institute of Polar Research)

3:45 PM - 4:00 PM

[MIS22-02] ICDP Drilling project to probe seismogenic zones of M2.0-5.5 earthquake in deep South African gold mines - Commencement of drilling.

*Hiroshi Ogasawara1,2, Yasuo Yabe3,1, Takatoshi Ito3, Gerrie van Aswegen4, Michelle Grobbelaar5, Raymond Durrheim6,1, Martin Ziegler7, Margaret Boettcher8, Tullis C Onstott9, Christo Craill5, Akimasa Ishida2, Hiroyuki Ogasawara2, Musa Manzi6, Harumi Kato10, Akio Funato11, Siyanda Mngadi6,1, Tatsunari Yasutomi12, Shigeki Horiuchi13, Alex Milev14,1, Pamela Moyer8, William Ellsworth15, Shuhei Abe3, Makoto Okubo1,16, Kazutoshi Imanishi1,17, Tony Ward18,1, Denver Birch5, Neta Wechsler19, Bennie Liebenberg20, Nicolas Berset7, John Paul Hunt5, Sifiso Bucibo5, Sylvester Morema18, Phil Dight21, Tom Kieft22, James Mori12, Harsh Gupta23, Christoph Janssen 24, Serge Shapiro25, Yusuke Mukuhira26, Stefan Wiemer7, Joachim Philipp28, Katrin Plenkers28, Makoto Naoi12,1, Hirokazu Moriya3,1, Kentaro Omura29, Surendra Nadh Somala 27, Kiyotoshi Sakaguchi3, Rachel Harris24,9, Errol Cason30, Esta van Heerden30 (1.JST-JICA SATREPS (2009-2015), 2.Ritsumeikan Univ., 3.Tohoku Univ., 4.Inst. Mine Seismol. Ltd, South Africa (SA), 5.Council for Geoscience, SA, 6.Univ. Witwatersrand, SA, 7.ETH, Switzerland, 8.Univ. New Hampshire, USA, 9.Princeton Univ., USA, 10.3D Geoscience Ltd, 11.Fukada Geol. Inst., 12.Kyoto Univ., 13.Home Seismo Ltd, 14.CSIR, SA, 15.Stanford Univ., USA, 16.Kochi Univ., 17.AIST, 18.Seismogen CC, SA, 19.Tel Aviv Univ., Israel, 20.Anglogold Ashanti, SA, 21.Western Australia Univ., 22.New Mexico Tech, USA, 23.Indian Geophys. Res. Inst., 24.GFZ, Germany, 25.Berlin Free Univ., Germany, 26.MIT, USA, 27.Indian Inst. Tech., India, 28.GMuG, Germany, 29.NIED, 30.Free State Univ., SA)

Keywords:ICDP, Seismogenic zones, Deep South African gold mines

The International Continental Scientific Drilling Program (ICDP) approved our proposal to drill into and around seismogenic zones where critically-stressed faults initiated ruptures at depth. The drilling targets include four ruptures equivalent to M2.0, 2.8, 3.5, and 5.5 earthquakes that dynamically and quasi-statically evolved in 2.9 Ga hard rock in the Witwatersrand basin, South Africa. A major advantage of our proposed project is the large quantity of high-quality data recorded by existing dense seismic arrays, both on surface and near-field underground, in three deep gold mines. Additionally, the great depths (1.0 to 3.3 km from surface) at which drilling starts reduces costs significantly and allows a larger number of holes to be drilled with the available budget. Flexibility in the drilling direction will also allow us to minimize damage to the borehole or the drilled cores. With ICDP funds, we will conduct full-core drilling of 16 holes at ranges of 50 to 750 m to recover both solid and fractured material in and around the seismogenic zones. This will be followed by core and borehole logging. Additional in-hole monitoring of rock deformation, ground motion, hydrology and geomicrobiology will be supported by co-mingled funds. We will also determine the 3D stress tensor near the collars of the holes using an overcoring technique that has been optimized for the highly-stressed ground and the working conditions found in deep South African mines. The measurement of the differential stress is based on the assumption that anisotropic variation in the diameter of the recovered core is caused by elastic expansion after drilling.

The M5.5 earthquake that took place near Orkney, South Africa on 5 August 2014 offers a special opportunity to compare models of the spatio-temporal evolution of both the main rupture and the aftershock activity determined by the inversion of ground motion measurements with direct observations.

Drilling will commence in early 2017.