Fig. 6 Logarithmic and exponential relationships between mean spacing,
computed Jv fracture density and the size of fallen
blocks as a function of distance from the fault core.
Using the Culmann method, we back-calculate bedrock mass strength based
on measurements of slope and relief of total 284 rockfall scars in the
WL region (Fig. 7). Values of cohesion (c) show a significant increase
with distance (d); they fit the power curve relation, c=208.64×d^0.12
(Fig. 8). In contrast, values of internal friction angle have a limited
range (23-28°) and do not change significantly with distance from the
fault core. Rock mass strength calculated by the Culmann method at
distances up to 5.3 km from the fault core is less than 300 kPa (Fig. 8)
and within the range of values estimated for hillslope-scale strength
(Schmidt and Montgomery, 1995). We attribute the low values of rock mass
strength to fault damage and use them to define a fault damage zone. At
distances > 6.5 km from the fault core, rock mass strength
significantly increases. Mean rockfall density calculated using the
spatial distribution of 407 rockfalls including 284 rockfall scars and
123 rockfall deposits (Fig. 1) by the bivariate kernel density
estimation tool in ArcGIS up to 6.5 km from the fault core is about
three times that beyond this distance (Fig. 8). Hence, we combined the
results of geometrical and mechanical analysis of rock mass
characteristics to estimate that the width of the damage zone of the
YLZP Fault is 5.9 ± 0.6 km (Fig. 8).