Landslide distribution and size versus relative relief (Shaanxi Province, China)

The present study aims to investigate the distribution and size of landslides in relation to relative relief. For this, a landslide inventory map of the area was developed from the interpretation of satellite images and detailed field survey. From this we could map 331 landslides in Ningqing County (Shaanxi Province). By using GIS and statistical approaches, we studied the coupling between landslide size distribution and relative relief. From this the control of relative relief on the rollover effect of the size distribution of landslides is obtained. The result shows that the landslide frequency-relative relief distribution is unimodal, with majority of landslides occurring in areas with relative reliefs in between 300 and 400. The relative number density of landslides decreased with the increase in the relative relief; on the contrary, the average area, average length and average width of landslide increased with the increase in relative relief. The percentage of large-scale landslide increased with the increase of relative relief or vice versa. In addition, the cumulative frequency-area distributions of these landslides empirically agree well with a power-law relation with an exponent of 1.776 above a certain size threshold. Below this value, it exhibited an obvious rollover effect. Further analysis has shown that landslide cumulative frequency-area curve is strongly influenced by relative relief. The rollover effect is more obvious with the increase of relative relief. The exponent of power law correlation gradually increased from 0.993 to 1.872 with increasing relative relief.