Fig. 9 Log–log plots of damage zone width against displacement of large
faults (>100 m displacement, Torabi et al., 2019) from the previous
studies and our study on YLZP fault.
We observe an inverse relationship
between mean slope angle and topographic relief in our study area (Fig.
7), consistent with the results of Schmidt and Montgomery (1995),
Frattini & Crosta (2013), Crosta et al. (2014), and DiBiase et al.
(2018). Hence, we infer that rock mass strength is an important factor
controlling relief in the area. However, Gabet et al. (2004) came to a
different conclusion, suggesting that annual rainfall, not rock mass
strength, is the controlling factor on relief in the Himalayas of
central Nepal, leading to the result that mean hillslope angles decrease
with increasing mean annual rainfall. In our whole study area, local
annual precipitation is uniform. This difference possibly is due to
different geological settings, climate conditions, and scales of the
studies. In our study area, intense tectonic activity within major fault
zones has affected the geometrical and mechanical characteristics of
rock mass. Research on differences in rock mass strength related to
different scales and different geological settings (e.g. tectonically
active sites) is a worthwhile future endeavor.
Previous studies (Khazai & Sitar,2004; Huang & Li, 2009; Qi et
al,.2010; Wang et al., 2020) have noted that faults have an important
influence on triggering landslides and rockfalls; some of these
researchers also discussed the relationships between number of
landslides and distance from a fault. However, the process of faults
controlling regional landslides and rockfall still suffers from a lack
of quantitative description. We quantitatively show that spatial
variation of the rock mass strength shows different trend within and
beyond the threshold distance due to the shift of geometrical
characteristics of rock mass structures controlled by the YLZP Fault
(Fig. 8). Correspondingly, the density of rockfalls shows a significant
shift at the threshold distance.