5:15 PM - 6:45 PM
[SCG42-P05] ICDP DSeis project: ITRAX XRF scan of the core drilled from the seismogenic zone of a magnitude 5.5 earthquake
Keywords:Seismogenic zones, ICDP drilling, Altered mafic/ultramafic intrusives
In 2014, an M5.5 left-lateral strike-slip earthquake occurred below the Moab Khotsong gold mine in South Africa—the aftershocks distributed on an NNW-SSE nearly vertical plane. The project "Drilling into Seismogenic zones of M2.0-5.5 earthquakes in South African gold mines (DSeis project)" recovered approximately 1.6 km of core from the upper margin of the aftershock zone of this earthquake and its surroundings, followed by the downhole logging for most of the drilled sections (Ogasawara et al. 2019; Nkosi et al. 2022).
Suzuki et al. (2022 JpGU) calibrated the 3D velocity structure of the 1996 3D seismic reflection survey data, elucidating the reflectors and their disruption lines in good harmony with the aftershock striations, reflective geological formations mapped at mining levels at 2-3 km depth, in the DSeis cores, and downhole logging.
In 2019, the DSeis team imported the most critical sections of the recovered cores (more than a hundred meters) to the Marine Core Research Institute, Kochi University, for analysis (e.g., Miyamoto et al. 2022).
The major 11-element XRF scans, μ-focus X-ray CT scans, EPMA, and SEM-EDS analyses have begun to reveal the physical, chemical, and mineral compositions and their spatial distributions in the host rock formations (Archean altered sedimentary rock; felsic) and mafic/ultramafic igneous intrusives. Then, a thin dike recovered where the drilling intersected the aftershock plane has SiO2~46wt%, Na2O+K2O~7wt%, CaO~10wt%, TiO2~2wt%, suggesting partial melting of upper mantle materials at great depth. On the boundary planes between this dyke and the host rock, the chemical/mineral boundaries of the host rock formations or those of the gravity differentiation boundaries within the mafic sill seem to control the aftershock activity streaks.
In October 2023, using the ITRAX XRF core scanner, we obtained spatial distributions of major elements heavier than Si to trace elements. This poster will report on what was seen in the results of this scan, corresponding to the above.
In JpGU2024, Fujita et al. will report the aftershock source DD-relocation around the borehole. Yabe et al. also report on the pre-proposal submitted to ICDP for the PROTEA project (PRObing The hEArt of earthquakes) that drills and probes the strong-motion sources of the M5.5 main shock. A kick-off meeting for the PROTEA project was successfully held in South Africa on January 22-24, and related meetings are being planned in Japan after JpGU 2024. Please refer to the PROTEA report for details.Please refer to these reports in conjunction with this report.
The DSeis team comprises seismologists, geologists, geomicrobiologists, rock mechanists, and mining engineers from Japan, South Africa, the USA, Switzerland, Germany, India, and Australia. The ICDP DSeis project is built on the JST-JICA SATREPS project and Kakenhi (21224012) projects. ICDP, JSPS, Ritsumeikan University, MEXT 2nd Earthquake and Volcano Hazard Reduction Research, US NSF, South Africa NRF, German DFG, Kochi Core Center, and Kyoto University also support it.
Suzuki et al. (2022 JpGU) calibrated the 3D velocity structure of the 1996 3D seismic reflection survey data, elucidating the reflectors and their disruption lines in good harmony with the aftershock striations, reflective geological formations mapped at mining levels at 2-3 km depth, in the DSeis cores, and downhole logging.
In 2019, the DSeis team imported the most critical sections of the recovered cores (more than a hundred meters) to the Marine Core Research Institute, Kochi University, for analysis (e.g., Miyamoto et al. 2022).
The major 11-element XRF scans, μ-focus X-ray CT scans, EPMA, and SEM-EDS analyses have begun to reveal the physical, chemical, and mineral compositions and their spatial distributions in the host rock formations (Archean altered sedimentary rock; felsic) and mafic/ultramafic igneous intrusives. Then, a thin dike recovered where the drilling intersected the aftershock plane has SiO2~46wt%, Na2O+K2O~7wt%, CaO~10wt%, TiO2~2wt%, suggesting partial melting of upper mantle materials at great depth. On the boundary planes between this dyke and the host rock, the chemical/mineral boundaries of the host rock formations or those of the gravity differentiation boundaries within the mafic sill seem to control the aftershock activity streaks.
In October 2023, using the ITRAX XRF core scanner, we obtained spatial distributions of major elements heavier than Si to trace elements. This poster will report on what was seen in the results of this scan, corresponding to the above.
In JpGU2024, Fujita et al. will report the aftershock source DD-relocation around the borehole. Yabe et al. also report on the pre-proposal submitted to ICDP for the PROTEA project (PRObing The hEArt of earthquakes) that drills and probes the strong-motion sources of the M5.5 main shock. A kick-off meeting for the PROTEA project was successfully held in South Africa on January 22-24, and related meetings are being planned in Japan after JpGU 2024. Please refer to the PROTEA report for details.Please refer to these reports in conjunction with this report.
The DSeis team comprises seismologists, geologists, geomicrobiologists, rock mechanists, and mining engineers from Japan, South Africa, the USA, Switzerland, Germany, India, and Australia. The ICDP DSeis project is built on the JST-JICA SATREPS project and Kakenhi (21224012) projects. ICDP, JSPS, Ritsumeikan University, MEXT 2nd Earthquake and Volcano Hazard Reduction Research, US NSF, South Africa NRF, German DFG, Kochi Core Center, and Kyoto University also support it.