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).