Distribution of Quaternary volcanic dike under the edifices and evaluation of central conduit stability by topographic analysis using contour lines

Nishiyama, Nariaki; Kawamura, Makoto; Umeda, Koji*; Niwa, Masakazu

Oyo Chishitsu, 64(3), p.98 - 111, 2023/08

https://doi.org/10.5110/jjseg.64.98

It is important to accumulate research examples on the spatial distribution of dikes under volcanic edifices for risk assessment in volcanic disaster prevention and site selection and safety assessment for the geological disposal of high-level radioactive waste. The topography of volcanoes is considered to represent the location of magma intrusion associated with volcanic activity and its history. In this study, we attempted to determine the predominant orientation of radial dikes and evaluate the central conduit stability based on the distribution, centroid, and area of contour lines comprising the volcanic edifices using GIS-based topographic analysis. As a result of the topographic analysis, the predominant orientation of the dikes was successfully shown for the volcanoes with stable conduits. On the other hand, this analysis was not suitable for determine the predominant orientation of dikes in volcanoes with unstable conduits, thus the applicable range of this analysis is considered to be determined by the conduit stability. In addition, the conduit stability can be evaluated by using the area data of contour polygons, which represents the scope of application to the method for determination of the predominant orientation of dikes. This means that the conduit stability during volcanic activity can be evaluated even for volcanoes of which activity history is not yet known, and that topographic analysis is a useful tool for this purpose. The use of topographic analysis in this study will be expected to provide a new scale for the history of volcanic activity.

Analytical method for chemical compositions of volcanic glasses in Tono Geoscience Center; Quantitative measurements of Major Elements by using EPMA and Minor Elements by LA-ICP-MS

Kagami, Saya; Yokoyama, Tatsunori; Umeda, Koji*

JAEA-Testing 2021-001, 49 Pages, 2021/08

JAEA-Testing-2021-001.pdf:3.86MB

To make a contribution to safety assessment for geological disposal of high level radioactive and/or TRU waste, we need to assess long-term stability of geological environment and predict long-term changes of geotectonic events that will occur in the future, especially for Quaternary period ( 2.6 million years ago-present). In the most case, we investigate chronological data of geological events by radiometric dating. When some geological samples have no objects to which radiometric dating method can be applied (e.g., zircon, biotite, wood fragments and plant residues), we can use tephrochronology, which is geological dating method using each layer of tephra (erupted volcanic ash), for dating of geological layers. This chronological method is essential in Japan, where volcanism is very active. Tephra is usually characterized by petrographic characteristics and/or chemical composition (mainly major elements) of volcanic glasses and/or minerals in tephra. In Tono Geoscience Center (Japan Atomic Energy Agency), we develop an analytical technique of chemical composition including trace elements of volcanic glasses for detailed tephra identification. In this paper, we report a sample preparation procedure and analytical methods of chemical compositions of individual volcanic glass shards by using an electron probe microanalyzer and a laser ablation-inductively coupled plasma-mass spectrometer.

Fission track dating of faulting events accommodating plastic deformation of biotites

Sueoka, Shigeru; Shimada, Koji; Ishimaru, Tsuneari; Niwa, Masakazu; Yasue, Kenichi; Umeda, Koji*; Danhara, Toru*; Iwano, Hideki*

Journal of Geophysical Research; Solid Earth, 122(3), p.1848 - 1859, 2017/03

http://doi.org/10.1002/2016JB013522

no abstracts in English

Annual report for research on geosphere stability for long-term isolation of radioactive waste in fiscal year 2015

Ishimaru, Tsuneari; Umeda, Koji*; Yasue, Kenichi; Kokubu, Yoko; Niwa, Masakazu; Asamori, Koichi; Watanabe, Takahiro; Yokoyama, Tatsunori; Fujita, Natsuko; Shimizu, Mayuko; et al.

JAEA-Research 2016-023, 91 Pages, 2017/02

JAEA-Research-2016-023.pdf:13.33MB

This annual report documents the progress of research and development (R&D) in the 1st fiscal year during the JAEA 3rd Mid- and Long-term Plan (fiscal years 2015-2021) to provide the scientific base for assessing geosphere stability for long-term isolation of the high-level radioactive waste. The planned framework is structured into the following categories: (1) Development and systematization of investigation techniques, (2) Development of models for long-term estimation and effective assessment, (3) Development of dating techniques. In this paper, the current status of R&D activities with previous scientific and technological progress is summarized.

Dating of crush zones associated with plastic deformation of biotite; Constraints by fission-track thermochronometry

Sueoka, Shigeru; Shimada, Koji; Ishimaru, Tsuneari; Niwa, Masakazu; Yasue, Kenichi; Umeda, Koji*; Danhara, Toru*; Iwano, Hideki*

Fisshion, Torakku Nyusureta, (29), p.5 - 7, 2016/12

http://ftrgj.org/FTNLs/FTNLparts/sueoka16.pdf

no abstracts in English

Cooling and denudation history of the Tsuruga body of Kojaku granite, southwest Japan, constrained from multi-system thermochronology

Sueoka, Shigeru; Umeda, Koji; Yasue, Kenichi; Niwa, Masakazu; Shimada, Koji; Ishimaru, Tsuneari; Danhara, Toru*; Iwano, Hideki*; Yagi, Koshi*

Chigaku Zasshi, 125(2), p.201 - 219, 2016/04

https://doi.org/10.5026/jgeography.125.201

We applied multi-system thermochronology to the Tsuruga body of the Kojaku granite to constrain the cooling/denudation history of the Tsuruga area. Based on the thermochronometric results and other data, we reconstructed the cooling and denudation histories of the Tsuruga body as below: (1) the Tsuruga body intruded at c.a. 68 Ma at the depth of 4-5 km, (2) rapidly cooled down to c.a. 200C by heat conduction within a few million years or less, and (3) slowly cooled due to peneplanation during the Cenozoic. This cooling/denudation history is consistent with the observations that cataclasite and fault gouge are dominant in the crush zones of the Tsuruga body, that similar slow cooling histories over the Cenozoic are estimated in the surrounding areas based on thermochronometric ages, and that the amount of denudation in the last few million years in the Tsuruga area is inferred at less than several hundred meters from the elevations of the uplifted peneplains.

Evaluation of dark current profile for prediction of voltage holding capability on multi-aperture multi-grid accelerator for ITER

Nishikiori, Ryo; Kojima, Atsushi; Hanada, Masaya; Kashiwagi, Mieko; Watanabe, Kazuhiro; Umeda, Naotaka; Tobari, Hiroyuki; Yoshida, Masafumi; Ichikawa, Masahiro; Hiratsuka, Junichi; et al.

Plasma and Fusion Research (Internet), 11, p.2401014_1 - 2401014_4, 2016/03

https://doi.org/10.1585/pfr.11.2401014

One of critical issues for high-energy high-current beam acceleration in ITER and JT-60SA is the high voltage holding which is dominated by vacuum discharges. The past results suggest that vacuum discharge occurs beyond the threshold of the dark current. The dark current can be derived from F-N theory where electric field enhancement factor beta is included. Though, beta could only be evaluated from the experiment previously. Therefore, the method to decide beta without experiment is required. This time dark currents were measured at three different areas to compare beta in different electric field. As a result, the effective electric field E, where E is average electric field, were found to be almost constant for different areas although the beta is largely different. By applying E, beta can be evaluated analytically, leading to the analytical prediction of the dark current and voltage holding capability without the measurements.

Measurement of heat load density profile on acceleration grid in MeV-class negative ion accelerator

Hiratsuka, Junichi; Hanada, Masaya; Kojima, Atsushi; Umeda, Naotaka; Kashiwagi, Mieko; Miyamoto, Kenji*; Yoshida, Masafumi; Nishikiori, Ryo; Ichikawa, Masahiro; Watanabe, Kazuhiro; et al.

Review of Scientific Instruments, 87(2), p.02B137_1 - 02B137_3, 2016/02

https://doi.org/10.1063/1.4935636

To understand the physics of the negative ion extraction/acceleration, the heat load density profile on the acceleration grid has been firstly measured in the ITER prototype accelerator where the negative ions are accelerated to 1 MeV with five acceleration stages. In order to clarify the profile, the peripheries around the apertures on the acceleration grid were separated into thermally insulated 34 blocks with thermocouples. The spatial resolution is as low as 3 mm and small enough to measure the tail of the beam profile with a beam diameter of 16 mm. It was found that there were two peaks of heat load density around the aperture. These two peaks were also clarified to be caused by the intercepted negative ions and secondary electrons from detailed investigation by changing the beam optics and gas density profile. This is the first experimental result, which is useful to understand the trajectories of these particles.

Development of design technique for vacuum insulation in large size multi-aperture multi-grid accelerator for nuclear fusion

Kojima, Atsushi; Hanada, Masaya; Tobari, Hiroyuki; Nishikiori, Ryo; Hiratsuka, Junichi; Kashiwagi, Mieko; Umeda, Naotaka; Yoshida, Masafumi; Ichikawa, Masahiro; Watanabe, Kazuhiro; et al.

Review of Scientific Instruments, 87(2), p.02B304_1 - 02B304_5, 2016/02

https://doi.org/10.1063/1.4931803

Optimization techniques of the vacuum insulation design have been developed in order to realize a reliable voltage holding capability of Multi-Aperture Multi-Grid accelerators for giant negative ion sources for nuclear fusion. In this method, the nested multilayer configuration of each acceleration stage in the MAMuG accelerator can be uniquely designed to satisfy the target voltage within given boundary conditions. The evaluation of the voltage holding capabilities of each acceleration stages were based on the past experimental results of the area effect and the multi-aperture effect on the voltage holding capability. Moreover, total voltage holding capability of multi-stage was estimated by taking the multi-stage effect into account, which was experimentally obtained in this time. In this experiment, the multi-stage effect appeared as the superposition of breakdown probabilities in each acceleration stage, which suggested that multi-stage effect can be considered as the voltage holding capability of the single acceleration gap having the total area and aperture. The analysis on the MAMuG accelerator for JT-60SA agreed with the past gap-scan experiments with an accuracy of less than 10% variation.

Localized extensional tectonics in an overall reverse-faulting regime, Northeast Japan

Umeda, Koji

Geoscience Letters (Internet), 2, p.12_1 - 12_8, 2015/11

https://doi.org/10.1186/s40562-015-0030-3

A particularly notable event was the shallow, normal-faulting earthquake swarms with a T-axis oriented in the E-W or NW-SE directions that occurred immediately after the 2011 Tohoku-Oki earthquake near the Pacific coast in the southeast Tohoku district. The stress tensor inversion represents the pre-Tohoku-Oki earthquake stress field in this area as a normal-faulting stress regime with the minimum principal horizontal stress oriented in a roughly NW-SE direction. Additionally, the stress regime varies with depth from normal faulting at shallow depths ( 15 km) to thrust faulting at greater depths. A plausible explanation for these drastic changes in the stress regime is upward flexure of the upper crust due to partly anelastic deformation in the weakened lower crust. Spatial variation of the late Pleistocene uplift rates near the Pacific coast in the southeast Tohoku district can be interpreted as the interaction between regional upwraping and localized extensional tectonics.