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.