A Case Study of Analysis of Faults in Neogene Siliceous Rocks

Abstract

In order to make features of small-scale faults of outcrop scale in Neogene siliceous rocks clear, outcrop observations, boring-core observations and borehole-wall image analyses were carried out, as a preliminary investigation for geological structure model construction which considers structures which exert big influence on flow and mass transfer of underground water. As a result, faults crossing a bedding plane at a high angle and faults parallel to a bedding plane were observed, and their formative process, origin, distribution and permeability were estimated. Faults crossing a bedding plane at a high angle tend to be distributed densely and to form a characteristic structure that is thought to contribute to a major water conducting feature.

Predictions of the highest potential transmissivity of fractures in fault zones from rock rheology: Preliminary results

“…Both sites contain fault zones comprising fault core(s) of incohesive fault rock (gouge/breccia) with a thickness of decimeters or less, together with surrounding damage zones with thicknesses of meters or less (where fractures are densely developed) [ Funaki et al ., ; Ishii , ; Ishii et al ., ; Mazurek et al ., ; Tokiwa et al ., ] (Table ). Very few mineral fillings are observed in the Wakkanai Formation at Horonobe, with just a few calcite veins (no more than one per 100 m length of borehole) and a small amount of calcite‐cemented fault breccia present [ Funaki et al ., , ; Ishii and Fukushima , ; Suko et al ., ]. Although numerous mineral veins are observed in the Palfris Formation at the Wellenberg site [ Nagra , ], only minute amounts of synfaulting to postfaulting calcite and pyrite are found on the fracture walls, and it is implied that water‐rock interactions during and after faulting were limited [ Mazurek , ].…”

“…Schematic diagrams of (a) opening of secondary fractures caused by shear-induced tensile stresses in a damage zone and (b) pore structures formed by mismatch of the shear-fracture walls. (c) Sketch of a sinistral strike-slip fault zone exposed at a horizontal outcrop in the Wakkanai Formation at the Horonobe site, and the directions of the maximum and minimum principal stresses (modified from Ishii and Fukushima [2006]). Barton [1976Barton [ , 2013, Ingram and Urai [1999], and Singh et al [2011].…”

The relationships among brittleness, deformation behavior, and transport properties in mudstones: An example from the Horonobe Underground Research Laboratory, Japan

“…On the basis of previous analyses of striations on the faults [ Ishii and Fukushima , 2006; Tokiwa et al , 2009], using the multiple inverse method [ Yamaji , 2000], σ 1 was nearly E–W and σ 2 was nearly vertical (or N–S), when the bedding planes were horizontal (i.e., at the time of maximum burial). Such a stress state is consistent with the above relationship between the orientations of the faults and the regional E–W compression.…”