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Niwa, Masakazu; Shimada, Koji; Terusawa, Shuji*; Goto, Akira*; Nishiyama, Nariaki; Nakajima, Toru; Ishihara, Takanori; Hakoiwa, Hiroaki
Island Arc, 33(1), p.e12516_1 - e12516_16, 2024/02
Times Cited Count：0To investigate the geological evidence of near-surface crustal deformations in a high-strain shear zone that has been geodetically identified but not associated with clear tectonic landforms, a fieldwork was conducted in E-W trending southern Kyushu high-strain shear zone, Japan. According to our study, an investigation based on the slip data from minor faults and the occurrences of fracture zones could help to identify a concealed fault that is small in terms of size to record tectonic landforms but can trigger large earthquakes.
Sueoka, Shigeru; Shimada, Koji; Terusawa, Shuji*; Iwano, Hideki*; Danhara, Toru*; Ogita, Yasuhiro; Hirata, Takafumi*
Chishitsugaku Zasshi, 127(1), p.25 - 39, 2021/01
no abstracts in English
Goto, Akira; Sasaki, Akimichi*; Komatsu, Tetsuya; Miwa, Atsushi*; Terusawa, Shuji*; Kagohara, Kyoko*; Shimada, Koji
JAEA-Research 2020-013, 88 Pages, 2020/11
JAEA-Research-2020-013.pdf:22.86MB
JAEA-Research-2020-013-appendix(CD-ROM).zip:0.18MB
Improvement of the investigation techniques to identify active faults is important for the implementation of geological disposal projects from the viewpoint of avoiding locations where permeability increases due to fault displacement. Generally, the existence of active faults is confirmed by aerial photography interpretation of fault displacement topography, which is a topographical trace of fault movement, and on-site geological surveys. However, the investigation method for cases where the topographical traces are unclear is not sufficiently developed. Therefore, to improve existing topographical methods, this study deciphered lineaments up to the rank of poorly defined features, which are almost neglected in general active fault research. The investigation area is one of the geodetic strain concentration zone, called the southern Kyushu shear zone, where the seismogenic faults of the 1997 Kagoshima northwest earthquakes are concealed. We conducted aerial photography interpretation of 62 sheets of 1/25,000 topographic maps, and obtained 1,327 lineaments. Distribution density, direction and length of lineaments were also investigated with topographic and geologic information. As a result, it was clarified that the east-west lineaments in the south Kyushu shear zone predominate in the western part, and the lineaments are densely distributed in the aftershock distribution area of the Kagoshima northwest earthquake. Along with these results, we have compiled a catalog of typical 13 lineaments based on combinations of clarity, direction, length and geomorphic characters of lineaments.
Goto, Akira; Murakami, Masaki*; Sakai, Ryutaro*; Terusawa, Shuji*; Sueoka, Shigeru
JAEA-Review 2020-003, 60 Pages, 2020/03
JAEA-Review-2020-003.pdf:4.43MB
One of the natural phenomena that may affect the geological disposal system are earthquake and fault activity. Fault displacement due to the earthquake and fault activity will be considered the direct effects. In addition to it, it is necessary to consider the secondary effects include secondary faults formed by the seismic fault activity as well as spring water and mud volcanoes that are generated by fluid movement attributed to the fault activity. This paper introduces previous studies performed focused on the hydraulic effects (spring water and mud volcanoes) and mechanical effects (secondary faults) in order to understand the effects of these secondary phenomena on the geological disposal system. We were able to collect 142 literatures from Japan and overseas by searching for related keywords in Japanese and English. As a result, we compiled case studies of each secondary impact. From the viewpoint of geological disposal, we extracted the following issues for future research and development. As for the sump water induced by earthquakes and faulting, accumulation of information related to its mechanism, affected area, and activity history is required. As for the mud volcanoes, reviewing of the mechanism of anomalous pore water pressure that causing the formation, also development of estimation technique are required. And for the secondary faults, accumulation of the detailed spatial distribution and reviewing of formation mechanism are required.
Terusawa, Shuji; Shimada, Koji
JAEA-Data/Code 2017-017, 18 Pages, 2018/03
JAEA-Data-Code-2017-017.pdf:5.14MBJAEA-Data-Code-2017-017-appendix(CD-ROM).zip:0.44MB
Cracks (joints, fracture zones, etc.) are formed in granite by various mechanisms. Faulting uses these pre-existing cracks as weak plane. In addition, there may be directionality in the direction of the crack, producing a linear valley. Attempts are also being made to estimate a regional stress field from the direction of excellence. In this paper, we developed a database of cracks in granite by compiling 5050 points of strike-dip data, as part of the geologic surveys of the Monju fast-breeder reactor located in the northwestern part of the Tsuruga Peninsula. The strike-dip is predominantly northern northeast to northeast strike and high angle east dip, but shows different characteristics for each place. Therefore, further analysis using this database is desired.
Shimada, Koji; Ishimaru, Tsuneari; Sueoka, Shigeru; Terusawa, Shuji; Yasue, Kenichi; Niwa, Masakazu; Umeda, Koji
no journal, ,
Diverse situation of outcropping crush zones around important building constructions need upgrading of activity evaluation method without the use of overlying sediments. The method using the cross-cutting relations among geologic features in basement rocks is promising. However, minor crush zones without cross-cutting relation are frequently observed. An activity evaluation of such minor crush zone was carried out in one outcrop. The confirmation of an extension of the crush zone, age estimation of young overlying sediments, comparison of sense of shear of clay vein, comparison of outcrop morphology with another crush zone, and clay grain-size measurement of the near active fault and the crush zone are carried out. The results suggest that the crush zone is not an active fault or a weak zone which slips accompanied with the active zone.
Shimada, Koji; Sueoka, Shigeru; Terusawa, Shuji
no journal, ,
Examples of meso- and microstructures of non-active minor crush zones are useful to an activity evaluation of minor crush zone. We show meso- and microstructures from minor crush zones in granite located near the prototype of fast breeder reactor Monju. A 1-cm-thick cataclasite zone exhibiting weakly localized strain was observed. Dynamic recrystallization of quartz is not observed. Biotite in the zone is typically stretched and defining foliation of the cataclasite. The coexistence of the intracrystalline plastic deformation of biotite and the crushing of other granular minerals in the foliated cataclasite indicates that the most recent slip is the semi-brittle flow. The deformation microstructure of biotite indicates that the deformation condition of the latest slip is high-temperature and the minor crush zone is non-active fault.
Terusawa, Shuji; Shimada, Koji
no journal, ,
The direction of the crack in the granite may have directionality, and it appears as a topography such as a linear valley. Attempts have been made to estimate stress field from the predominant direction. We compiled the results of geological survey which was conducted near the Monju cite in 2007 to 2015, and extract the predominant direction of cracks. As a result, in the northeastern area of the survey area, the north northeast and the west northwest direction were predominant, in the southwest, the northeast and the northwest direction were predominant. The included angle was about 60 to 80 degrees in the northeastern area and about 90 degrees in the southwestern area, and the dip angle was 60 to 80 degrees in both areas. The differences in the predominant direction in the northeastern part and the southwest part may proved by surveys which focusing on the presence or absence of minute displacement of individual joints, more extensive survey.
Shimada, Koji; Terusawa, Shuji
no journal, ,
Representativeness of the crush zone for activity evaluation at the Monju site was investigated by means of statistics of length distributions. The length distribution was exponential indicating a coalessence stage of the crush zone development. Thus the choice of the crush zone to be evaluated during our preceded research (2012-2016) was reasonable. We also payed attention for the future systematic and practical survey from the view point of superposed deformation. That is, in our experience, a superposed deformation observed at the weakest portion in the crush zone system, suggesting that the research on the longest crush zone with an attention at the weakest zone preferable for superposed deformation seems to be a practical research procedure.
Shimada, Koji; Goto, Akira; Sasaki, Akimichi*; Terusawa, Shuji*; Komatsu, Tetsuya
no journal, ,
We tried an objective expression of directional distribution of lineaments utilizing the directional statistics for the high interpretability. Directional statistics of lineaments at the shear zone in southern Kyushu indicate that the length weighted directional distribution of lineaments are decomposed into five von Mises distributions. An objective extraction of the East-West lineament concentration ereas was concordant with qualitative understanding by means of rule of thumb, judgement at a glance or rose-diagram.
Higa, Saki*; Terusawa, Shuji*; Niwa, Masakazu; Shimada, Koji; Komatsu, Tetsuya
no journal, ,
In the southern Kyushu shear zone, geological investigation along north-south ca.27 km area near aftershock distributions of the 1997 Kagoshima-ken hokubu earthquake depict striation and sense of shear of small faults. As a result of stress inversion analysis, it was found that the NE-SW compression and NW-SE tension stress fields, consistent with the left-lateral shear of the southern Kyushu shear zone, is localized within central 2 km north-south width zone.
Sasaki, Akimichi*; Komatsu, Tetsuya; Miwa, Atsushi*; Terusawa, Shuji*; Kagohara, Kyoko*; Higa, Saki*
no journal, ,
no abstracts in English
Goto, Akira; Shimada, Koji; Niwa, Masakazu; Terusawa, Shuji*
no journal, ,
Owing to a nationwide GNSS network installed since mid-1990s, high-strain shear zone with a sinistral strike-slip was identified in southern Kyushu. There have had large earthquakes in this area such as the 1997 Northwestern Kagoshima Earthquake, however, any seismogenic faults associated with these earthquakes or active faults with strike-slip tectonic landforms had not been previously recognized at the surface. Mesoscale fault zones with clayey gouge and cataclasite are rare in the study area (northwestern Kagoshima (22
16 km)). Instead, minor faults cutting bedding planes and deformation structures subparallel to the bedding, suggesting the formation clearly after the accretion of the Shimanto accretionary complex, are commonly observed. Slip directions can be examined from striations along the minor faults. Based on orientation data of these striations, we applied stress tensor inversion techniques to elucidate stress states. Our field survey revealed an occurrence of the E-W trending zone of 
2 km wide showing a stress state consistent with the sinistral high-strain shear zone (NE-SW compression and NW-SE extension). This study can contribute to one of helpful approaches to examine potential future activities of faults (or shear zones) without clear tectonic landforms.
Terusawa, Shuji*; Shimada, Koji
no journal, ,
The Dip Azimuth Vector plots used in resource exploration was utilized to visualize the dominant fracture direction trends at each depth section of borehole data taken from the Monju site. This procedure is one of the domain analysis method of granite. Domain boundaries are intersections of the two dominant fracture orientations providing pipe-like flow paths of groundwater. So, utilization of geological data accumulated at the Monju in this way, contributes application for geological survey for disposal of HLW as well as ground safety assessment for large earthquakes.
Niwa, Masakazu; Shimada, Koji; Goto, Akira; Terusawa, Shuji*
no journal, ,
Owing to a nationwide GNSS network, several highstrain shear zones defined as concentrated regions of strain rates have been recognized in Japanese Islands. The high-strain shear zone with a sinistral strike-slip was identified also in southern Kyushu. However, any active faults with strike-slip tectonic landforms had not been previously recognized at the surface. In this study, we focused on existing minor faults to clarify a geological evidence of the shear zone suggested by geodetic studies. Based on orientation data of striations on the faults, we applied stress tensor inversion techniques to elucidate stress states. Our field survey revealed an occurrence of the E-W trending zone of approximately 2 km wide showing a stress state consistent with the sinistral high-strain shear zone. This study can contribute to one of helpful approaches to examine potential future activities of faults (or shear zones) without clear tectonic landforms.
Shimada, Koji; Takeuchi, Ryuji; Omatsu, Keita*; Terusawa, Shuji*; Uehara, Yasuhiro*
no journal, ,
We retrieved 2 boring cores of basement rocks of granite from the Monju (prototype FBR at the Tsuruga city, the shore on the Sea of Japan) site. Excavation lengths are 100m and 200m. Objectives of the drilling are presence check of weak zones that could became as slip plane for slope failure, and large crush zones. Because of the presence of these zones can be problems for large-building constructions, we were asked for prompt confirmations. We tried, therefore, to measure the weight of each 1m core of granite during geological classification of the rock grades. The average wet density and data range of each rock classes as follows, classes B: wet density 2.53 (g/cm
, same as below); range 0.10, CH: 2.51; 0.11, CM: 2.48; 0.42, CL: 2.42; 0.11. The decreased density (less than 2.42 g/cm) continuous zone of 5m (44-49m in depth of 100m hole) is corresponds to brecciated deterioration. This low-density zone is, however, shorter than the example of the Nojima active fault which possesses a few decameter scale zone, and discontinuous to the next 200m hole (distance between the two holes is about 30m). Therefore, the data identified do not show any large-scale weaknesses that would pose an immediate problem for the construction of heavy structures.
