1) Construction of geological model using data from literature survey and other geoscientific researches

As for the granite, the primary tectonic elements generated during the formation include lithofacies, while the secondary ones generated after the formation include weathered parts, fractures and faults. Though different lithofacies are recognized in the granite through the existing investigations and analyses, enough information is not obtained for a deterministic modeling of their distribution and continuity. As for fault, it is only the Tsukiyoshi Fault that the distribution is ascertained. Thus, the following three elements for the modeling are set in the granite: fractured zone including the weathered part, the rest of the granite and the Tsukiyoshi Fault.

Geological model of the Shobasama site is shown in Fig.4.19. Here, 3-D visualization software is not used for this model for the reasons that sufficient tectonic elements can not be extracted in the granite and the software is not introduced then.

Uncertainties in the geological model are as follows.

Data on the heterogeneity of the granite deep underground are scarce. As a result, the granite could be divided only into two elements : the fractured zone including the weathered part and the rest of the granite.
Information on the Tsukiyoshi Fault is not available in the granite. Thus, it is postulated that the fault in the granite has the same properties as that in the sedimentary rocks.

2) Construction of geological model using data including the result of the Phase I-a

(1) Extraction of geological unit

For sedimentary rocks, lithofacies are extracted as primary elements whereas fractures and faults are extracted as secondary elements generated after their formation. Based on the correlation between stratigraphy and permeability, the sedimentary rocks are divided into Seto Group, Oidawara Formation, Akeyo Formation, Toki Lignite-bearing Formation and Tsukiyoshi Fault.

Based on the borehole investigations of the MIU-13, following improvements are carried out.

As secondary tectonic elements produced after the formation of the granite, the weathered part, the "Upper fracture zone", the Tsukiyoshi Fault, and the "Fracture zone along the fault" are set. Since the "Upper fracture zone" is thought to be characterized by a high fracture density and permeability, it is distinguished from the Biotite granite and Felsic granite. As the Tsukiyoshi Fault is accompanied with an ca.100m-wide fracture zone, the "Fractured zone along the fault" is set on the both sides of the fault.
Resultantly, geological units set for the granite are the weathered part, the "Upper fracture zone", the Tsukiyoshi Fault, "Fracture zone along the fault", the Biotite granite and the Felsic granite.

Fracture distribution based on the above-mentioned properties of fractures is schematically shown in Fig.4.20.

(2) Model construction

On the basis of a data shown in Tab.4.11, boundaries of the individual geological units and the shape of the fault plane are estimated using the minimum tension theory. This model construction is carried out in an area of ca.0.8kmca.1.3km (henceforth "modeling area") encompassing the Tsukiyoshi Fault (Fig.4.21). This modeling area is presumed to greatly affect the hydrogeology of the Shobasama site and to be used for the groundwater flow simulation in the future (See Chapter 4.2.4). Data used for the modeling are shown in Tab.4.11. However, data set obtained from the MIU-3 is prepared too late for the modeling to be used. Methods to set the above-mentioned boundaries are as follows.

Topographical surface
Digital elevation data shown in Tab.4.11 (interval of 20m) are used.

Boundary between the Seto Group and the Oidawara Formation
The Oidawara formation is restricted to the footwall (north side) of the Tsukiyoshi Fault, and as a result, it is not encountered in the boreholes drilled in the Shobasama site. For the modeling, the digital information of the boundary drawn in a geological map of the Toki-Mizunami district is used.

Boundary between the Seto Group and the Akeyo Formation
This boundary is so shallow at the drilling sites in the Shobasama site that no core is recovered. For the modeling, the digital information of the boundary drawn in a geological map of the Toki-Mizunami district is used.

Boundary between the Akeyo Formation and the Toki Lignite-bearing Formation
The depth of this boundary is determined by the results of the MIU-1 and MIU-2 borehole investigations. On the other hand, the Toki Lignite-bearing Formation is distributed neither in the AN-1, AN-3 nor on the ground surface. Thus, on the assumption that the boundary doesn't extend to the AN-1 and the AN-2, the depth information obtained in the MIU-1 and the MIU-2 are used for the modeling.

Boundary between the sedimentary rocks and the weathered part of the granite
The depths of this boundary are confirmed by the results of the MIU-13, AN-1 and AN-3 borehole investigations. The upper part of the granite exposed on the ground surface is thought to be weathered. Accordingly, the depth information obtained in the boreholes and the digital information drawn in a geological map of the Toki-Mizunami district are used for the modeling.

Boundary between the weathered part of the granite and the "Upper fracture zone"
Zones with following characteristics are defined as weathered parts of the granite.
a zone with grade CM or below by the Denken rock grading
a zone dominated by RQD (total length of 10cm-long or more cores obtained during drilling per a meter) of less than 50%
a zone characterized by low resistivity, low density and high porosity in geophysical loggings
a zone in the granite near the boundary with the sedimentary rocks. The matrix in this zone contains limonite and kaolinite⁴²⁾, which are thought to be generated by weathering.
Following the above definitions, the thickness distribution of the weathered part of the granite is estimated based on the results of the MIU-1, MIU-2, AN-1 and AN-3 borehole investigations.

Boundary between the "Upper fracture zone" and the "Moderately fracture zone" of the Biotite granite
The "Upper fractured zone" is here defined as a zone characterized by a higher fracture density, a higher porosity in geophysical logging, and/or the more frequent occurrence of horizontal fractures than the "Moderately fracture zone". This boundary is modeled using the information obtained from the MIU-1 and the MIU-2 borehole investigations.

Boundary between the "Upper fracture zone" and the "Moderately fracture zone" of the Felsic granite
This boundary is modeled using the information obtained from the AN-1 and the AN-3 borehole investigations.

Boundary between the "Moderately fracture zone" of the Biotite granite and the "Moderately fracture zone" of the Felsic granite
These are not distinguished on the existing geological map¹³⁾. As a result, this boundary is modeled using the information obtained from the MIU-1, MIU-2, AN-1 and AN-3 borehole investigations.

The Tsukiyoshi Fault
The depth of the Tsukiyoshi Fault is confirmed in the MIU-2, whereas it is not verified in the adjacent MIU-1. Therefore, the depth information in the MIU-2 and the digital information of the fault line on the existing geological map¹³⁾ are input to the modeling. For modeling, 30m of the displacement by the Tsukiyoshi Fault is postulated for the following boundaries on the both sides of the fault
boundary between the Akeyo Formation and the Toki Lignite-bearing Formation
boundary between the sedimentary rocks and the underlying weathered granite
boundary between the weathered granite and the "Upper fracture zone"
boundary between the "Moderately fracture zone"s of the Biotite and Felsic granites.
However, the genetic relationship between the "Upper fracture zone" and the Tsukiyoshi Fault is unknown. Therefore, the fault displacement of the boundaries between the "Upper fracture zone" and "Moderately fracture zone"s of the Biotite granite and the Felsic granite are not considered.

Upper boundary of the "Fracture zone along the fault" (hanging wall side of the Tsukiyoshi Fault)
The information on thickness of the "Fracture zone along the fault" on the hanging wall side is obtained only in the MIU-2. Accordingly, the modeling of this boundary is carried out under the assumption that the thickness of the fractured zone in the MIU-2 would extend throughout the modeling area.

Lower boundary of the "Fracture zone along the fault" (footwall side of the Tsukiyoshi Fault)
The "Fracture zone along the fault" is confirmed on the footwall side of the Tsukiyoshi Fault in the MIU-2. However, its lower boundary is too deep to provide the thickness information. Consequently, it is postulated that the fractured zone on the footwall side of the fault has the same thickness as that on the hanging wall side.

^{* :} 1/25,000 "Toki" and "Mizunami"published by Geophysical Survey Institute

Uncertainties in the geological model are as follows.

The data on the northeastern part of the Shobasama site are insufficient.
Since the MIU-13 are all vertical, the information on fractures with a high inclination is insufficient.
The information on the thickness variation of the "Fracture zone along the fault" is insufficient.
Local inhomogeneity of the individual geological units of the granite are insufficiently expressed.
No information at 1,000m in depth or below is available.