Fig. 4 Coltop images (a) in colours representing the local orientation of five joint sets (b) at five sites (Fig. 1 and Fig. 3) and stereographic projections (c). At each site, a window of 100 ⅹ 100 ⅹ 100 m was selected for measuring the dip/dip direction (c) and spacing of all visible rock mass joints.
The J1 to J5 joint set spacing and their mean values at each site was measured as shown in Fig. 5 and Table 1. Influenced by tectonics, the relationship between mean spacing of joint sets with distance from the fault core show a strong positive power relationship (Fig. 6). The rock mass exposed at site 3 in contrast to the other four sites is predominantly gneiss (Fig. 1). The rock strength of the gneiss measured on site by Schmidt hammer testing (Aydin & Basu 2005) is lower than that of diorite and granite. As observed at site 3, the spacing of the joint sets within gneiss is smaller relative to the same joint sets in the diorite under the similar condition of tectonism (Fig. 5). For consistency here we only considered the spacing of the joint sets within the same diorite lithology in building the relationship. The joint volumetric count, Jv, at varying distance (d) from the fault core is calculated using the joint set spacing (Table 1) and shows a strong negative power relationship (Fig. 6) albeit with relatively large variability at site 1. There is also a marked exponential relation between the mean size of fallen blocks and distance from the fault core (Fig. 5 and Fig. 6). This indicated that the sizes of the rockfall blocks and the joint set spacing agree well even when they are obtained by different methods.