Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Satake, Hiroshi*; Kita, Yuichiro*; Hayashi, Haruna*; Murata, Masanobu*
Geodynamics of Atotsugawa Fault System, p.123 - 148, 2007/00
no abstracts in English
Hirahara, Kazuro*; Ozono, Mako*; Sagiya, Takeshi*; Hoso, Yoshinobu*; Wada, Yasuo*; Ando, Masataka*
Geodynamics of Atotsugawa Fault System, p.25 - 44, 2007/00
no abstracts in English
Tanaka, Hidemi*; Ito, Tanio*; Nohara, Tsuyoshi; Ando, Masataka*
Geodynamics of Atotsugawa Fault System, p.103 - 121, 2007/00
The Mozumi-Sukenobe fault, running ENE-WSW and dipping almost vertically, is one of the Atotsugawa right-lateral active faults in central Japan. A 500 m long horizontal tunnel was excavated across the Mozumi-Sukenobe fault, utilizing the pre-existing tunnel of the Kamioka Mine for geological and geophysical integrated research of the fault zones. In order to clarify the fault zone architecture and rock distribution, we have investigated the distribution across the tunnel and obtained samples directly from the tunnel. The following results were obtained by meso-and microscopic observations and mineralogical examination of fault rocks; (1) Two fracture zones (referred to as zones A and B) are distinguished. They are 15 and 50 m in thickness, respectively, composed of foliated fault breccia in a damaged zone and foliated fault gouge in the fault cores. The core-zones contain an 8 cm slip layer for zone A and several thin (10 cm) slip layers for zone B. (2) Most of the fault rocks obtained from the fault cores of the two fracture zones show a distinct foliated texture, which is clearly a product of cataclastic flow deformation. Very thin, ultra-fine grained slip layers, generated by seismic rapid slip, are also detected from fault core of zones A and B. The cross-cutting relationship between foliated and rapid slip textures indicate a repeated process of slow and rapid slips in zones A and B. (3) The results of mineral assemblage analysis show that these fault rocks are dominated by smectite clay minerals as well as by mica minerals and chlorite, all of which could be potential candidates for the main reason of the stable slip. Combining all these data, we conclude that the Mozumi-Sukenobe fault is activated by extremely slow frictional-viscous creep which releases crustal strain energy. However, stress would also be released by earthquakes based on the existence of earthquake slip surfaces in the fault cores of the Mozumi-Sukenobe fault.
Takeuchi, Akira*; Takebe, Akimitsu*; Ongirad, H.*; Doke, Ryosuke*
Geodynamics of Atotsugawa Fault System, p.1 - 10, 2007/00
no abstracts in English
Doke, Ryosuke*; Takeuchi, Akira*
Geodynamics of Atotsugawa Fault System, p.11 - 16, 2007/00
no abstracts in English
Azuma, Shunichi*; Ishii, Hiroshi*; Asai, Yasuhiro*; Kitagawa, Yuichi*; Wakita, Hiroshi*; Yamauchi, Tsuneo*; Asamori, Koichi
Geodynamics of Atotsugawa Fault System, p.173 - 179, 2007/00
no abstracts in English
Ito, Kiyoshi*; Wada, Hiroo*; Omi, Shiro*; Hirano, Norio*; Ueno, Tomotake*
Geodynamics of Atotsugawa Fault System, p.45 - 63, 2007/00
The seismicity in the Atotsugawa fault area is studied in detail from the data of dense network stations, together with temporary station data. Since the observation network has been improved by adding new stations, the accuracy of the hypocenters has been accordingly raised by using the dense network data of temporary observations conducted by the Frontier Project. As a result, the distribution of hypocenters has greatly improved to reveal regional changes in focal depths along the fault. Besides, the characteristic features of seismicity along the Atotsugawa fault system are well derived from the high frequency and high-gain observations for about the last 30 years. Each distribution of focal depths along the Atotsugawa and Mozumi-Sukenobe faults is found to be vertical in the seismogenic zone of 15 km in depth from the detailed analyses of hypocenters. The distance between the two faults is 8 km at most. hypocenters are relatively deeper in the northwestern side of the fault zone compared to those in the southeast of the fault. These observation results, together with those of the GPS observations, lead to a model of the strain concentration along the fault zone. The model contains a detachment dipping towards the northwest in the middle or in the lower crust, where no earthquakes occur. In the Hida Mountains, shallow seismicity is well correlated with volcanoes. The seismicity in the mountains is different from those of the tectonic event for their focal depth and a maximum event size of M5.5. Detailed surveys in the Tateyama volcano area show that focal depths of earthquakes become shallower stepwise from the Atotsugawa fault system to the Hida Mountains. This suggests that the Atotsugawa fault ends at the foot of the Tateyama volcano.
Ito, Kiyoshi*; Ueno, Tomotake*; Wada, Hiroo*; Matsumura, Kazuo*
Geodynamics of Atotsugawa Fault System, p.65 - 78, 2007/00
The Atotsugawa fault system is a well-known active fault and the only active fault with a creeping section in Japan. Besides, the fault area is also thought to be a part of the "Niigata-Kobe Tectonic Zone" (NKTZ). Although seismic activities and crustal movements in the fault area have been well-studied in recent years, the mechanism of the strain concentration along the area is not still unknown. Therefore, we analyzed seismic explosion data along and across the fault system to reveal the relationship between crustal structures and seismic activity. P-wave velocity and reflectors in the crust are derived from the seismic surveys of 2000 and 2001. Furthermore, seismic surveys carried out in the Chubu district are re-analyzed to reveal reflectors in the crust. We obtained the followings for the structures and earthquake distribution along and across the fault: Most earthquakes occur only in the layer with a P-wave velocity of 6.0-6.2 km/s and seismicity is very low in the surface layer with a P-wave velocity of less than 5.8 km/s. Two distinct reflectors are located at depths of about 12-15 and 18-21 km in the crust. The shallower reflector seems to be roughly coincident with the base of the seismogenic layer and the other in the mid-crust by about 8-10 km below the cutoff of the seismicity. These two reflectors have also been found in wide areas in the Chubu district from the seismic surveys in 1981 and 1991, although the depth varies from place to place. The velocity between the two reflectors seems to be of intermittent value between the upper and lower crustal layers. The cutoff of seismicity seems to be coincident with the upper reflector.
Nishigami, Kinya*
Geodynamics of Atotsugawa Fault System, p.79 - 83, 2007/00
no abstracts in English
wavesNishigami, Kinya*; Fujisawa, Izumi*; Tadokoro, Keiichi*; Mizuno, Takashi*; Mamada, Yutaka*
Geodynamics of Atotsugawa Fault System, p.85 - 92, 2007/00
no abstracts in English
Nishigami, Kinya*; Ito, Hisao*; Kuwahara, Yasuto*; Mizuno, Takashi*; Mamada, Yutaka*
Geodynamics of Atotsugawa Fault System, p.149 - 156, 2007/00
no abstracts in English
Mamada, Yutaka*; Nishigami, Kinya*; Ito, Hisao*; Kuwahara, Yasuto*
Geodynamics of Atotsugawa Fault System, p.93 - 102, 2007/00
The explosion experiments at the Mozumi-Siukenobe fault enabled us to collect high quality records using the linear seismometer array installed in an underground tunnel at a depth of 300 m. The seismograms contained high frequency components of up to 25 Hz. The phases interpreted as fault zone head waves, direct-
waves propagating within the fault zone, and fault zone trapped waves were clearly found on the seismograms. Using such high quality records, we could perform fault zone wave modeling. We successfully simulated almost the characteristics on the observed seismograms with high frequency components of up to 25 Hz and revealed the complex structure of the Mozumi-Sukenobe fault zone terminating just east of the site SP1. This indicates the possibility of modeling for high frequency seismic waves that excited at the fault zone. According to this modeling, the precise -waves velocity adjacent to the fault zone and velocity contrast of waves between the wall rock and fault zone were estimated. The modeling also indicates the possibility of detecting fault zone discontinuity, in other words, the segmentation of fault at depth.
Yanagidani, Takashi*; Yamashita, Futoshi*
Geodynamics of Atotsugawa Fault System, p.181 - 186, 2007/00
no abstracts in English
Kano, Yasuyuki*; Yanagidani, Takashi*; Kitagawa, Yuichi*; Yamashita, Futoshi*
Geodynamics of Atotsugawa Fault System, p.163 - 171, 2007/00
no abstracts in English
Ito, Tanio*; Tsumura, Noriko*; Takeuchi, Akira*; Ishimaru, Tsuneari; Takami, Akira*; Ikawa, Hidemasa*; Komada, Nozomi*; Yamamoto, Shuji*; Kikuchi, Shinsuke*; Miyauchi, Takahiro*; et al.
Geodynamics of Atotsugawa Fault System, p.17 - 24, 2007/00
no abstracts in English
Ishii, Hiroshi*; Yamauchi, Tsuneo*; Asai, Yasuhiro*; Matsumoto, Shigeo*; Mukai, Atsushi*
Geodynamics of Atotsugawa Fault System, p.157 - 162, 2007/00
Investigation of the behavior of stress and strain in the vicinity of active faults provides valuable data. We have performed continuous strain observation and stress measurements in the active Mozumi-Sukenobe Fault. Two strain meters were installed on both sides of the crushed zones. Characteristic strain variations on both sides indicate right lateral movements that are almost identical to the movements of the fault. The stress measurements also indicate the same pattern as the fault movements, although the values are smaller than usual. The reason proposed is that the crushed zone of the fault can not accumulate stress. The behavior of strain variation suggests that fault movements are caused by the actions of tectonic stress but that the accumulation of this stress is small in the vicinity of the fault stress.