Characteristics and formation process of fractures in crystalline rocks in northern Kyushu

Murakami, Hiroaki; Ashizawa, Masaomi*; Tanaka, Kazuhiro*

Oyo Chishitsu, 59(1), p.2 - 12, 2018/04

This study describes the features of fractures and their fillings along with the long-term behavior of their hydrogeological structures in an underground environment based on the results of a geological investigation conducted at an underground facility in northern Kyushu. Fractures were classified into five groups on the basis of fracture orientation: A, B, C, D, and low-angle groups. The genesis of all fractures is the cooling process of granodiorite pluton. Almost all of the water-conducting fractures are included in the B group. Because a number of fracture fillings in the B group are filled by prehnite and crushed fragments of epidote and quartz, the fractures in this group alternated sealing and re-opening. The fracture characteristics in the B group are follow as: accompanying many alteration halos, long trace length, and cutting off other fractures. These results indicate that fractures in the B group have possibly functioned as pathways for groundwater flow in the long term.

None

Shimo, Michito*; *

JNC TJ7400 2000-008, 157 Pages, 2000/03

JNC-TJ7400-2000-008.pdf:4.02MB

no abstracts in English

Characteristics and formation processes of water-conducting fractures in the Hyuga Group of the Shimanto Belt

Ono, Takuya; Yoshida, Hidekazu*

no journal, , 

Very few studies have been performed to reveal characteristics and evolutions of water-conducting fractures in sedimentary rocks of accretionary complexes. Accretionary complexes can be a proposed site for geological disposal in Japan. Because of such backgrounds, we investigated fractures in borehole cores excavated from the Hyuga Group of the Shimanto Belt in the south of the Kyushu Island. Microscopic observation, SEM observation, XRD analysis and XRF analysis of minerals in/around fractures revealed characteristics of water-conducting fractures in accretionary complex and a process of fracture sealing according to carbonate mineral precipitation.

Fracture domain of granite based on orientation analysis and its relation to water conducting fractures; An Example from the "-500m access/research gallery-North" of the Mizunami Underground Research Laboratory

Shimada, Koji; Niwa, Masakazu; Takeuchi, Ryuji; Amano, Kenji

no journal, , 

Domain analysis of granite on the basis of fracture orientation in the 100 m scale by means of structural geologic techniques such as stereographic projection, Strike Versus Traverse Distance diagram and Sequential Linked Median (SLIME) plot revealed relationship between distribution of water conducting fractures and fracture orientations. This attempt used fracture data taken from the "-500m access/research gallery-North" of the Mizunami Underground Research Laboratory. Improvement of the SLIME plot based on running median of span 3 shows water conducting fractures are concentrated at domain boundaries. A location of one of the large kinks corresponds to a region of fractures with geochemical high connectivity from deeper parts.