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.