Geometric models and property assignment

Sixty deformation zones, the majority of which have been assigned a high confidence of existence, are included in the local model, stage 2.2 /Stephens et al. 2007/. Inspection of the orientation plot (Figure 5-28a) indicates that these zones are predominantly vertical or steeply dipping, with WNW, NW, ENE (NE) and NNE sub-sets, or gently dipping with dips to the south and SE. A few deformation zones that are vertical or steeply dipping and oriented NNW or E-W are also present (Figure 5-28a). The frequency of the vertical and steeply dipping zones increases as their surface length decreases and the size of these zones follows a power-law distribution with a slope of 1.08 (Figure 5-28b).

Both the orientation and size distribution of the vertical and steeply dipping zones, in the regional model, strongly resemble the equivalent parameters in the local model (Figure 5-28a, b and c).

However, relative to the local model, the regional model is characterised by a higher proportion of vertical and steeply dipping zones in the WNW and NW sub-sets and an increased proportion of gently dipping zones /Stephens et al. 2007/. The modelling work inside the local model volume also identified several minor fracture zones with trace lengths at the ground surface shorter than 1,000 m /Stephens et al. 2007/. These zones are vertical or steeply dipping and belong predominantly to the ENE to NNE set (Figure 5-28d). A few minor zones that are oriented NNW, WNW and E-W are also present.

1 10 100

1,000 10,000 100,000

Deformation zone length [m]

Complementary-cumulative number of deformation zones

DZ length in the regional model, kt = 1.14 DZ length in the local model, kt = 1.08

c d

a b

The vertical or steeply dipping deformation zones in the sub-sets referred to as WNW and NW, occur in the south-western and north-eastern peripheral parts of the local model volume, i.e. along or outside the margins of the Forsmark tectonic lens (Figure 5-29). Several of these zones have trace

Figure 5‑29. Vertical or steeply dipping deformation zones included in the three dimensional local model, stage 2.2. In the upper model figure (viewed to the north), zones marked in red have a trace length at the ground surface longer than 3,000 m and zones marked in green are between 1,000 and 3,000 m in trace length. The orientation of fractures inside the different sets or sub-sets of vertical or steeply dipping deforma-tion zones, which are included in the local model (stage 2.2), are plotted as poles to planes in stereographic projections (equal-area, lower hemisphere) and contoured. A Terzaghi correction has been applied in these plots. The fracture mineralogy along each set or sub-set is also shown and the order of mineral presentation reflects the order of abundance (based on Figure 5-18 and Appendix 17 in /Stephens et al. 2007/). The zones in each orientation set or sub-set are distinguished in the lower model figure (viewed to the north). In this figure, red = WNW to NW set, yellow = ENE (NE) sub-set, green = NNE sub-set and blue = NNW set.

500 m

500 m

NNW set

Fracture mineralogy chlorite-calcite-adularia-hematite-laumontite-quartz

NNE sub-set

Fracture mineralogy chlorite-calcite-adularia-hematite-laumontite-quartz

Fracture mineralogy

calcite-chlorite-adularia-hematite (clay minerals-laumontite-quartz-prehnite-pyrite-epidote)

Fracture mineralogy

calcite-chlorite-laumontite-adularia-hematite (pyrite-quartz-clay minerals-prehnite-epidote)

ENE (NE) sub-set WNW-NW set

Forsmark nuclear power plant

Steeply dipping deformation zones

Forsmark nuclear power plant

Singö deformation zo ne (WNW0001)

WNW0123 ENE0060A

ENE0062A Singö deformation zo

ne (WNW0001)

WNW0123 ENE0060A

ENE0062A

lengths at the ground surface longer than 3,000 m. These zones follow the general structural trend defined by rock contacts and the ductile planar grain-shape fabric. The subordinate set of vertical and steeply dipping fracture zones referred to as NNW also follows the ductile fabric in the bedrock.

By contrast, inside the local model volume and tectonic lens, where the ductile fabric is folded and more variable in orientation (see section 5.2.4), the bedrock is intersected, more or less exclusively, by vertical or steeply dipping zones that are included in the ENE (NE) and NNE sub-sets

(Figure 5-29). The zones in these two sub-sets are distributed in clusters inside the local model volume. Most conspicuously, there is a concentration of ENE (NE) zones in the south-eastern part and NNE zones in the central part of the local model volume (see also /Stephens et al. 2007, p. 165/).

The surface trace length of these zones is predominantly between 1,000 and 3,000 m (Figure 5-29).

Although the position and trace length of several lineaments were modified in connection with an evaluation of the complementary, high-resolution ground magnetic data acquired during stage 2.3, the overall implications for the stage 2.2 geological modelling work are limited in character /Stephens et al. 2008/. In particular, no new deformation zones with a trace length at the ground surface longer than 3,000 m have emerged. The data acquired along borehole KFM08D during stage 2.3, following the establishment of the deformation zone model /Stephens et al. 2007/, confirm the significance of ENE and NNE deformation zones with a trace length shorter than 3,000 m inside the target volume (/Stephens et al. 2008/ and section 5.8). Furthermore, the new data acquired along boreholes KFM11A and KFM12A constrain the properties of the regionally significant Singö and Forsmark zones /Stephens et al. 2008/.

The majority of gently dipping deformation zones are situated outside or in the south-eastern, peripheral part of the local model volume (Figure 5-30a). Only zones A2, A8, B7, F1, 1203 and possibly B4 merit closer attention in the repository design work. From north to south in the south-eastern part of and outside the local model volume, zones A8, A2, F1 and A3 appear to splay off each other in an integrated mesh (Figure 5-30b). In particular, zone A2 in this family defines the roof of the volume that has been identified as potentially suitable for the excavation of a repository /SKB 2005c/. The gently dipping zones A8, B7 and 1203 occupy restricted volumes at predominantly shal-low crustal levels in this volume (Figure 5-30a). The data acquired along borehole KFM02B during stage 2.3 have confirmed the occurrence of the gently dipping zones 866, A3, A2 and F1 beneath drill site 2 /Stephens et al. 2008/.

The properties of deformation zones included in the deterministic models at different scales were presented in Appendix 15 in /Stephens et al. 2007/. Most of the data have been acquired from the local model volume. In addition, the properties of some minor deformation zones with surface trace lengths shorter than 1,000 m, which are located in the local model volume, were presented in Appendix 16 in /Stephens et al. 2007/. Compilations of fracture orientation, fracture mineralogy and the orientation of fractures separated on the basis of fracture mineralogy in each set (or sub-set) of deformation zones were presented in section 5.3.2 and Appendix 17 in /Stephens et al. 2007/.

A generalised summary of the properties for each set (or sub-set), based on these detailed property tables, is presented below.

The geological and hydrogeological properties of the zones that are present at 400 to 600 m depth, inside the potential repository volume, are compiled in Appendix 4. This compilation makes use of an integration of stage 2.2 and stage 2.3 geological and hydrogeological data and stage 2.2 modelling results. The zones in this compilation belong, more or less exclusively, to the vertical or steeply dipping ENE to NNE set.

Vertical or steeply dipping zones in ENE to NNE set

The vertical or steeply dipping deformation zones in the ENE to NNE set have been studied along four excavations at the surface and along several intersections in virtually all the cored boreholes

Figure 5‑30. a) Gently dipping deformation zones on both sides of the Singö zone (WNW0001) extracted from the three dimensional regional model for deformation zones. The orientation of fractures inside the gently dipping deformation zones, which are included in the local model (stage 2.2), are plotted as poles to planes in a stereographic projection (equal-area, lower hemisphere) and contoured. In order to limit the bias that is related to the orientation of boreholes, a Terzaghi correction has been applied in this plot. The fracture mineralogy in the gently dipping zones is also shown and the order of mineral presentation reflects the order of abundance (based on Figure 5-18 and Appendix 17 in /Stephens et al. 2007/). b) Apparent splay-like pattern between zones A2, A8, F1 and A3 in the south-eastern part of and outside the local model volume. Boreholes KFM02A and KFM02B and three of the boundaries to the local model volume are also shown. The boundary of the local model volume to the north lies outside the view of the figure.

Fracture mineralogy

calcite-chlorite-adularia-hematite-(clay minerals-laumontite-pyrite-quartz-prehnite-asphaltite-epidote)

a

KFM02A KFM02B

Local model volume

b