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.
Ota, Kunio; Abe, Hironobu; Yamaguchi, Takehiro; Kunimaru, Takanori; Ishii, Eiichi; Kurikami, Hiroshi; Tomura, Goji; Shibano, Kazunori; Hama, Katsuhiro; Matsui, Hiroya; et al.
JAEA-Research 2007-044, 434 Pages, 2007/03
The Horonobe URL Project started in 2000. Research and development activities are planned over three phases, that will span a total duration of about 20 years: the 1st surface-based investigarion phase (6 years), the 2nd URL construction phase (8 years) and rhe 3rd operation phase (12 years). Geological, geophysical, geo-mechanical, hydrogeological, and hydro-geochemical investigations have been carried out during the surface-based investigation.
Shirato, Nobuaki*; Matsui, Hiroya; Morioka, Hiroshi; Hatanaka, Koichiro; Takeuchi, Ryuji; Hatakeyama, Nobuya; Ohara, Hidefumi; Nakajima, Takahiro; Kunitomo, Takahiro
JNC-TN5440 2005-001, 412 Pages, 2005/06
We held Horonobe technical review meeting 4 times a year. The first meeting is for the plan of Horonobe underground research laboratory and others. The secound meeting is for geology of Horonobe area and modeling study and data acquisition for safety assessment methodology and others. The third meeting is for ventilation network analyses on URL plan. The fourth meeting is for the remote monitoring system using ACROSS. This report is records of these meetings.
Birkhaser, P.*; Lacave, C.*; Ohara, Hidefumi; Niizato, Tadafumi
JNC-TY5410 2005-001, 26 Pages, 2005/04
The goal of this study was to determine the frequency dependent amplification function by calculation of the ratio between the surface response spectrum and the response spectrum at depth. A 1D model (CyberQuake) was used for the computations, because it could be concluded from the local geology that there are no significant 2D effects to be expected. Acceleration time histories from a weak motion local earthquake at a depth of 13 and 16 km recorded on July 20th (M 0.7) and August 18th (M 0.8) 2003 and from the Tokachi off-shore earthquake to the south of Hokkaido located some 430 to 450 km away from the borehole, recorded on September 26th (M 8.0) plus an aftershock recorded on September 27th 2003 were available as input data. All events are characterised by rather small acceleration values. The amplifications seem to be magnitude dependent. With the data at hand, the observed amplification functions are however rather unstable, showing different shapes for the different earthquakes and for two components of a single event. The observed ground motion amplification was much higher than the one calculated. Possible explanations for the observed discrepancy are (1) an incorrectness in the derivation of the input S-wave velocity profile used for the calculations of this study, or (2) problems with the recording instruments It is therefore recommended to check the basis of the derivation of the S-wave velocity input data and, if possible, perform direct S-wave downhole logging or S-wave crosshole measurements. It is further recommended to plan for an installation of high quality accelerometers in the future JNC Horonobe URL shaft. Additional measurements of field data would allow to record a more reliable dataset for proving and characterising significant attenuation of earthquake accelerations with depth, which also will be an important argument for feasibility studies related to the site investigations for geological disposal elsewhere in Japan or worldwide.
Ohara, Hidefumi; Tsukui, Rota; Kunitomo, Takahiro; Nakajima, Takahiro; Niizato, Tadafumi; Aoki, Kazuhiro; Shigeta, Naotaka; Kumazawa, Mineo
no journal, ,
Japan Atomic Energy Agency (JAEA) is developing a remote monitoring system using seismic and electromagnetic ACROSS(Accurately Controlled Routinely Operated Signal System), to monitor changes in the geological environment. ACROSS has been researched and developed in Tono Geoscience Center for 9 years, and we introduce it to the Horonobe Underground Research Laboratory (URL) project. The Horonobe URL project is devoted to the technological development over 20-years from March 2001 for a safe geological disposal of high level radioactive wastes in Horonobe-cho in northern Hokkaido, Japan. We install the monitoring system before the shaft excavation, and collect data before, during and after the excavation, in order to permit assessment of the system's reliability. The source and receivers of electromagnetic ACROSS were installed in the winter before last, and we are carrying out the test of the system. In last December, the source and receivers of a seismic ACROSS were installed in Horonobe. Then we are going to examine the practicability of ACROSS.
Moriya, Hirokazu*; Niizato, Tadafumi; Kitamura, Itaru*; Hotta, Hikaru*; Ohara, Hidefumi
no journal, ,
The source locations of earthquakes at the Horonobe area, north of Hokkaido, Japan have been relocated by using the multiplet-clustering analysis (MCA) to identify the subsurface structures and to reveal the mechanism of earthquakes. The absolute source locations of 221 earthquakes were determined by the "hypomh" algorithm to find the overall structures in this area. After that, those earthquakes were classified into 10 groups of multiplets which are the groups of events with very similar waveforms and their source locations have been relocated based on the MCA in order to reveal the fine scale structures. The multiplet-clustering analysis has revealed that the earthquake locations show the structures trending from NS to NNE-SSW with reverse or strike-slip focal mechanism.
Kunimaru, Takanori; Ota, Kunio; Abe, Hironobu; Yamaguchi, Takehiro; Ishii, Eiichi; Kurikami, Hiroshi; Tomura, Goji; Shibano, Kazunori; Hama, Katsuhiro; Matsui, Hiroya; et al.
no journal, ,
The Horonobe Underground Research Laboratory (URL) Project is being pursued by the Japan Atomic Energy Agency (JAEA) to enhance the reliability of relevant disposal technologies through investigations of the deep geological environment within the host sedimentary formations at Horonobe, northern Hokkaido. The project consists of two major research areas, "Geoscientific Research" and "R&D on Geological Disposal", and proceeds in three overlapping phases, "Phase I: Surface-based investigation", "Phase II: Construction" and "Phase III: Operation", over a period of 20 years. The present report summarises the results of the Phase I geoscientific research carried out from March 2001 to March 2005. Integration of work from different disciplines into a "geosynthesis" ensures that the Phase I goals have been successfully achieved and identifies key issues that need to be addressed in the Phase II/III investigations.
Sanada, Hiroyuki; Hanakawa, Toshiyuki; Ota, Kunio; Abe, Hironobu; Yamaguchi, Takehiro; Kunimaru, Takanori; Ishii, Eiichi; Kurikami, Hiroshi; Tomura, Goji; Shibano, Kazunori; et al.
no journal, ,
no abstracts in English
Asamori, Koichi; Kunitomo, Takahiro; Nakajima, Takahiro; Ohara, Hidefumi*; Shigeta, Naotaka; Watanabe, Toshiki; Kumazawa, Mineo
no journal, ,
The electromagnetic (EM) and seismic ACROSS have been installed around the Horonobe Underground Research Laboratory and experimental monitoring prior to the construction of the underground facilities was started. The EM and seismic ACROSS are consisted a transmitter and 3 receiver stations. These receivers are about 1-2 km away from the transmitter. The observed spectrum by operating ACROSS show that the amplitude of frequency bands correspond to the transmitted signal are higher than that of other frequency bands. It is indicates that the transmitted signal was certainly received.
Moriya, Hirokazu*; Asamori, Koichi; Kitamura, Itaru*; Hotta, Hikaru*; Ohara, Hidefumi*; Niizato, Tadafumi
no journal, ,
Hypocenter locations of shallow earthquakes in Horonobe area were determined to reveal the mechanisms of earthquake occurrence. The absolute source locations of 211 earthquakes were determined; then, those earthquakes with similar waveforms were identified, and the source locations of 26 multiplet groups were relocated by using cross-spectrum and clustering analyses. The relocated hypocenters allowed two seismically active areas to be identified, at 10-20 km and around 25-30 km depth. The earthquake locations indicate structures trending nearly N-S, and the structures causing repeated stick-slips at asperities, thus generating similar earthquakes.