Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Ogawa, Hiroki; Hama, Yuki*; Asamori, Koichi; Ueda, Takumi*
Butsuri Tansa, 75, p.38 - 55, 2022/00
In the magnetotelluric (MT) method, so as to identify the subsurface resistivity structure, the apparent resistivity and phase profiles are calculated by transforming time-series data into spectral data. The continuous wavelet transform (CWT) is well known as a new method of time-frequency analysis instead of the short-time Fourier transform. The CWT is superior in processing non-stationary wideband signals like the MT signal by adjusting the size of the wavelet according to the value of frequency. However, the calculation settings of the CWT, such as the type of basis function and the wavelet parameter, are often determined empirically because of the arbitrariness of the shape of the wavelet. Although there might be differences between the calculated MT responses and the true responses due to improper settings of the CWT, there are no detailed studies considering the effect of numerical errors derived from spectral transforms on MT data. In this study, focusing on the frequency band between 0.001 Hz and 1 Hz, we examined the optimum calculation settings of the CWT in processing MT data in terms of suppressing the numerical errors caused by the spectral transform of time-series data. We also show the validity of the proposed calculation settings by applying the CWT to MT survey data of different types. Superiority of the CWT with proposed settings is suggested especially when the signal-to-noise ratio of observed data is low. Consequently, the proposed calculation settings were confirmed to strike a balance between the resolutions of the time and frequency domains well and will therefore be effective in obtaining reliable MT responses.
Kubota, Kenji*; Aoyagi, Kazuhei; Sugita, Yutaka
Koeki Shadan Hojin Butsuri Tansa Gakkai Dai-138-Kai (Heisei-30-Nendo Shuki) Gakujutsu Koenkai Koen Rombunshu, p.51 - 54, 2018/05
In an excavation of shafts and galleries in the deep underground for disposing high level radioactive waste, an excavation disturbed zone (EdZ) or excavation damaged zone (EDZ) is developed around the shafts and galleries owing to the stress redistribution. It is important to understand the behavior of the EdZ or EDZ because these zone could have an effect on the transfer behavior of radioactive nuclide. Therefore, the authors performed the in situ experiment to investigate the behavior of EdZ or EDZ in the 140m and 250m gallery in the Horonobe Underground Research Laboratory. From the result of the experiments, the authors compared the characteristics of EdZ or EDZ between those in 140m and 250m gallery. The extent of the fractures induced by the gallery excavation, i.e., EDZ was about 0.45m in the 140m gallery and about 1m in the 250m gallery. The extent of the unsaturated zones related with EdZ was about 1m in the 140m gallery, however, unsaturated zone was not appeared in the 250m gallery.
Yanagizawa, Koichi; Hayashi, Toshio*; Oinuma, Masaru*; Takemori, Makoto*; Ishikawa, Takanori*; Okaya, Tomoichi*; Nishigaki, Makoto*
Shadan Hojin Butsuri Tansa Gakkai Dai-129-Kai (Heisei-25-Nendo Shuki) Gakujutsu Koenkai Koen Rombunshu, p.287 - 288, 2013/10
The development of instrument aimed at the measurement of radiation dose in the sediment of lakes, rivers and sea bed been carried out. The radiation level contained in the sediment at the bottom of lake and so on is anticipated to indicate the existence of locally high radiation spots where the diffused radioactive substance is accumulated in ponds, rivers and lakes by rainwater. The radiation dose measurement system this time is to measure 
-ray by dragging the detector, which is called probe, at the bottom of lakes to understand the radiation dose over wide areas. Furthermore, the measurement of resistivity value at the bottom of lakes is simultaneously dose to presume the condition of sediment.
Suzuki, Keiichi*; Onuma, Hiroshi*; Takegami, Hiroaki; Takamatsu, Kuniyoshi; Hino, Ryutaro; Okumura, Tadahiko*
Shadan Hojin Butsuri Tansa Gakkai Dai-129-Kai (Heisei-25-Nendo Shuki) Gakujutsu Koenkai Koen Rombunshu, p.131 - 134, 2013/10
In the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, the nuclear fuel had melted down due to loss of coolant and had already become debris. The debris would fall to the bottom of the CV. To remove the debris for future decommission is necessary; however the area and the size are unclear. On the other hand, cosmic ray muons are absorbed extremely in the debris because of the high density of uranium and plutonium. The inner structure of the nuclear reactor may be visualized with muons penetrating easily throught such the high-density material, as a non-contact or -destructive inspection. In this study, the muons through the HTTR were measured and visualizing the internal structure was attempted. As a result, high density areas were recognized at the same position as that of the reactor pressure vessel (RPV); therefore, the technical possibility with muons could be demonstrated. In the near future, new R&Ds will be promoted toward the practical use.
Kubota, Kenji*; Kondo, Keiji; Sakakibara, Junichi*
Shadan Hojin Butsuri Tansa Gakkai Dai-128-Kai (Heisei-25-Nendo Shuki) Gakujutsu Koenkai Koen Rombunshu, p.62 - 65, 2013/06
To evaluate the excavated damaged zone (EDZ) is one of the important factors to conduct high level radioactive waste disposal. We have conducted resistivity and acoustic tomography to evaluate EDZ during the excavation of the test tunnel at a depth of 140 m and 250 m. As a result, a few meters extent of high resistivity and low P-wave velocity zone were detected at a depth of 140 m. This suggests that EDZ by excavation of horizontal tunnel was estimated by resistivity and acoustic tomography. On the other hand, high resistivity zone were not detected at a depth of 250 m.
Soma, Nobukazu*; Oikawa, Yasuki*; Hirano, Toru*; Matsui, Hiroya; Asanuma, Hiroshi*
Butsuri Tansa, 66(2), p.69 - 83, 2013/04
We have studied a reflection imaging technique in which passive seismic signals from other construction activity such as drilling noise are used as a wave source in order to develop a low-cost measurement method inside underground gallery. In this paper, we show an application to data sets from Mizunami Underground Research Laboratory of Japan Atomic Energy Agency. The drilling was conducted with a main purpose of extraction rock core samples for rock mechanics research. The three-dimensional reflection imaging results and comparison with well observation are shown in this paper.
Negi, Tateyuki; Umeda, Koji; Matsuo, Koichi*; Asamori, Koichi; Yokoi, Koichi*; Ohara, Hidefumi*
Butsuri Tansa, 64(2), p.153 - 165, 2011/04
The wide band MT method is recognized as an effective method for identifying deep resistivity structures in the crust. In the method, natural variations in the electric and magnetic fields of the earth are acquired over a wide range of frequencies. World wide, thunderstorm activity produces magnetic fields at frequencies above 1Hz. These natural phenomena create strong MT source signals over the entire frequency spectrum. However, magnetic fields at frequencies below 1Hz activate intermittently, because they are caused by the interaction between solar wind and the magnetosphere and therefore, long recording times are required to obtain usable readings. In noisy regions, the signals may be contaminated by DC train signals and other coherent noise, such as occur in western Japan. When magnetic field data are contaminated by such noise, it is difficult to remove or segregate the contaminated data from the usable data. In the paper, we showed the validity of the new weighted stacking method using survey data contaminated by coherent noise.
Negi, Tateyuki; Umeda, Koji; Matsuo, Koichi*; Asamori, Koichi; Yokoi, Koichi*; Ohara, Hidefumi
Butsuri Tansa, 63(5), p.395 - 408, 2010/10
In the MT-survey, it is important for the reliability evaluation of inversion result to evaluate acquired data quality. We suggested new reliability parameters, "Predict Phase Error (PPE)", "Acquired Curve Roughness (ACR)", "Error Bar Level (EBL)" to evaluate acquired data quality that was depend on the skill and experience of MT surveyor. We examined the relation between noise level and numerically expressed parameters. As a result, extremely high correlation coefficient was recognized between noise level and PPE. PPE was expected available parameter to evaluate the noise level of acquired MT data. We suggested combination of PPE, ACR, and EBL to keep the objectivity and stability for the reliability evaluation.
Shigeta, Naotaka
Saishin No Butsuri Tansa Tekiyo Jireishu, p.61 - 68, 2008/10
Despite of a short history of uranium exploration, many deposits were found during just fifty years or so since the start of survey operations by making full use of geophysical surveys. For the efficient exploration considering the diversity of the deposits, it is indispensable to select an exploration flow based on establishing an appropriate model of physical properties of a uranium deposit and regional characteristics such as surface conditions. In 1990s PNC was establishing or restructuring exploration flows on unconformity-related deposits, of which type has been positioned prior to all in terms of economical merit. Deposit models and exploration flows should be revised constantly by solving various technical issues basing on the latest interpretation of obtained data. On and after 1990s, the deposit discovery rate is strikingly decreasing. This fact indicates that we are in the phase where major revises of models and exploration flows are required.
Shigeta, Naotaka
Saishin No Butsuri Tansa Tekiyo Jireishu, p.257 - 264, 2008/10
Geological environments are required mainly two functions in terms of ensuring the safety for geological disposal of high-revel radioactive waste. One relates to long-term stabilities of a site and the other to properties of host rocks and groundwater that facilitate the emplacement and function as natural barrier. Geophysical surveys are expected to play important roles providing both implementation and safety regulation with information on deep geological environments. Japan Atomic Energy Agency, from the era of its predecessors, is carrying out studies on systematic methodology for evaluating geological environments. Useful knowledge including on geophysical survey has been obtained through the studies.
Yamanaka, Yoshiaki; Matsuoka, Toshiyuki; Asamori, Koichi; Ota, Kunio
Shadan Hojin Butsuri Tansa Gakkai Dai-119-Kai (Heisei-20-Nendo Shuki) Gakujutsu Koenkai Koen Rombunshu, p.73 - 75, 2008/10
Characterisation of the coastal geological environment has now been running since July 2007 at Horonobe, northern Hokkaido, with the main aims of establishing a comprehensive coastal site characterisation technology and enhancing its reliability. Work carried out to date involves a survey and interpretation of the existing information, identification of key investigation issues and planning of ground exploration. Development of technical know-how and decision process for the work, in particular the geophysical surveys, has been initiated to provide "knowledge" to support a site characterisation project.
Hodotsuka, Yasuyuki; Matsuoka, Toshiyuki; Tsuruta, Tadahiko; Yamada, Nobuto*; Ishigaki, Koichi*; Yamaguchi, Shinji*
Shadan Hojin Butsuri Tansa Gakkai Dai-119-Kai (Heisei-20-Nendo Shuki) Gakujutsu Koenkai Koen Rombunshu, p.61 - 64, 2008/10
Seismic interferometry using the vibration under the construction works such as borehole drilling, mucking, blasting etc., had been carried out to develop the method that obtain three-dimensional geological image, around the Mizunami Underground Research Laboratory. In this study, we discussed the applicability of this method analytical accuracy depending on vibration resource types.
Matsuoka, Toshiyuki; Hodotsuka, Yasuyuki; Tsuruta, Tadahiko; Ishigaki, Koichi*; Yamada, Nobuto*; Yamaguchi, Shinji*
Shadan Hojin Butsuri Tansa Gakkai Dai-119-Kai (Heisei-20-Nendo Shuki) Gakujutsu Koenkai Koen Rombunshu, p.65 - 67, 2008/10
A reverse VSP (R-VSP) using the blasting vibration been carried out to obtain three-dimensional geological image around the Mizunami Underground Research Laboratory under the shaft excavation works. In this study, the applicability of this method was discussed.
Negi, Tateyuki; Umeda, Koji; Asamori, Koichi
Shadan Hojin Butsuri Tansa Gakkai Dai-118-Kai ((Heisei-21-Nendo Shunki) Gakujutsu Koenkai Rombunshu, p.198 - 201, 2008/05
MT-survey is used to be applied to the investigation of the geothermal resource, mineral resource, and oil. In recent years MT-survey has also been recognized as an effective method for the investigation of deep geological environments. However, due to the nature of magnetotulluric source, it is difficult to maintain data quality at all time in extremely noisy environment. Furthermore, expansion of urban area will provide an opportunity to acquire MT data in such environment. Therefore, it is important to be able to evaluate the uncertainly of inversion result using poor quality data. We show the new method of the uncertainly assessment of MT inversion results.
Negi, Tateyuki; Umeda, Koji; Matsuo, Koichi*; Asamori, Koichi
Shadan Hojin Butsuri Tansa Gakkai Dai-117-Kai (Heisei-19-Nendo Shuki) Gakujutsu Koenkai Koen Rombunshu, p.195 - 198, 2007/10
MT survey has been applied to various fields in recent years. It is recognized as effective method to know deep resistivity structure. However, it is difficult to acquire interpretable quality data in highly noisy environments, because natural electromagnetic fields are used in the MT survey. To apply MT survey in such environments, it is important to develop robust stacking method to improve the quality of MT spectrum data. In the last SEGJ conference held in Spring 2007, we have reported effective robust stacking method based on MT reliability index shown in Negi et al (2005). In the fall conference, we report the development of robust smoothing method of MT data to compile with the robust stacking method. As a result of application to poor quality data, it was improved to interpretable quality data in short time. Therefore, it is expected to be effective and practical stacking method for the poor quality data.
Yamada, Nobuto*; Ishigaki, Koichi*; Yamaguchi, Shinji*; Narita, Norifumi*; Matsuoka, Toshiyuki; Hodotsuka, Yasuyuki; Matsuoka, Toshifumi*
Shadan Hojin Butsuri Tansa Gakkai Dai-117-Kai (Heisei-19-Nendo Shuki) Gakujutsu Koenkai Koen Rombunshu, p.146 - 148, 2007/10
Seismic interferometry synthesizes the Green's function between two receivers by calculating cross-correlation of records measured at their locations. In Japan Atomic Energy Agency(JAEA), Seismic Interferometry using blasting vibration caused by the shafts excavation had been carried out to investigate the geologic structure in the surrounding area. The result was identical to the existing seismic reflection section. In this study, we applied this technique to long time measured microtremor. The result was also identical to the results of existing section and seismic interferometry using blasting vibration caused by the shafts excavation.
Hasegawa, Ken; Matsuoka, Toshiyuki; Yuki, Yoichi*
Shadan Hojin Butsuri Tansa Gakkai Dai-116-Kai (Heisei-19-Nendo Shunki) Gakujutsu Koenkai Rombunshu, p.159 - 162, 2007/05
An airborne electromagnetic survey was conducted in the region of the Toki granite. The resistivity of the Toki granite about is about 5000 
m while the resistivity of the Mizunami Group and the Seto Group which overlie the Toki granite is tens of m. Due to processing limitation, this large contrast in resistivity was not included in past calculations of apparent resistivity. A new calculation method for apparent resistivity was developed, and data was reprocessed. As a result, the regions where the thickness of the Mizunami and/or the Seto Group is thin (the depth of the Toki granite is shallow) and the regions where the Toki granite is deep were clearly identified.
Hasegawa, Ken; Matsuoka, Toshiyuki; Yuki, Yoichi*
Shadan Hojin Butsuri Tansa Gakkai Dai-116-Kai (Heisei-19-Nendo Shunki) Gakujutsu Koenkai Rombunshu, p.163 - 166, 2007/05
Airborne magnetic and radiometric surveys were conducted in the region of the Toki granite. The shaded relief map of the magnetic survey data shows that the magnetic susceptibility of the Toki granite is not uniform, and a relatively high magnetic susceptibility zone was identified. Moreover, it was shown that the Toki granite can be separated into three parts; one with high U abnormality, another with high Th abnormality, both separated by a middle region. The area with high magnetic susceptibility in the Toki granite correspond to where the thickness of the layer of the Mizunami and/or the Seto Group is thin and the depth of the Toki granite is shallow, and the region corresponds to high U abnormality. We conclude the Toki Granite is not homogeneous with respect to geophysical properties, but instead is composed of separate regions.
Yoshimura, Kimitaka*; Sakashita, Susumu*; Okubo, Shuichi*; Yamane, Kazunobu*; Seya, Masami
Shadan Hojin Butsuri Tansa Gakkai Dai-115-Kai (Heisei-18-Nendo Shuki) Gakujutsu Koenkai Rombunshu, p.209 - 212, 2006/10
3D MT inversion development has been conducted to solve issues in electromagnetic exploration in the radioactive waste disposal area. Radioactive Waste Management Funding and Research Center (RWMC) operated field work to confirm how the 3D inversion code worked in low resistivity geology at Horonobe area, Hokkaido in 2005 and applied the code to AMT data. Data suggests possibility to estimate salinity of groundwater in the area of lower resistivety than 1ohm-m.
