# Influence of Earthquakes on Landslide Susceptibility in a Seismic Prone Catchment in Central Asia
## 4 Discussion
### Landslide Susceptibility Index and Volume of Landslide  
Referring to the specificity of geologic and natural conditions, the Mailuu-Suu catchment is a region with frequent high-seismic and geodynamic activities [13; 48; 52]. The landslide susceptibility assessment by means of LSI and VOL indicates the probability of landslides in this catchment. The floodplain at the mouth of the Mailuu-Suu catchment was identified as the most stable zone. This area is mainly flatland near the Ferghana Valley. The identification of floodplain as the stable zone was also reported in the Chittagong Hilly Areas of Bangladesh by [PERSON] and [PERSON] [42]. The vulnerable areas to landslide were found to be dominated in the upstream areas (Figure 3). This is slightly different from the findings of [PERSON] et al. who reported that landslides frequently occurred in the mid-stream of the Mailuu-Suu [50]. A possible reason for the different findings lies in the definition of the upstream and mid-stream areas. In the present study, the defined upstream areas included both high and moderate mountain (i.e., mid-stream) areas. In addition, the Scoops3D model considers the influence of groundwater on local landslides as well. This makes the simulation more precise than the method of geological survey [33]. As an advantage of Scoops3D, a series of earthquake scenarios, ranging between moderate (M 5.0) and extreme (M 9.0), can be incorporated into the scenario analysis. It is reasonable that the values of LSI reduced with the increase in earthquake level, and a similar finding was reported by [PERSON] et al. [56]. Under the most frequently occurred earthquake level in the Mailuu-Suu catchment (i.e., the moderate earthquake scenario), the downstream areas were stable or very stable, where most residents and a large number of radioactive tailing ponds exist, indicating the relatively low influence of landslides on society and radioactive problems in this catchment. Nevertheless, this general spatial pattern would be quite different once the hazard level rises; for example, under the extreme earthquake scenario, the entire Mailuu-Suu catchment was classified as unstable area in the aspect of LSI.  
Similar patterns of LSI were not observed for the VOL in this catchment. The VOL did not rise substantially with the increase in the earthquake level under M 8.0 (i.e., from moderate to violent). The VOL was, however, significantly higher under the extreme scenario than under the other four scenarios. By means of differential synthetic aperture radar interferometry analysis, [PERSON] et al. [52] found slow displacements of soil columns and concluded the existence of long-term slow sliding activities in the Mailuu-Suu catchment. Under the effect of low earthquake strength (e.g., moderate to severe), the VOL maintained a low level with a low number of mosaic clusters. With the triggering of violent or extreme earthquakes, these long-term slow displacements of soil columns could change into a catastrophic release of volume with a large number of mosaic clusters, as indicated in this case study. Besides the effect of earthquakes, a large number of landslides were caused by other types of hazards in this catchment. For example, in April 1958, about 50% of tailing materials were released from the radioactive tailing pond 7 into the nearby river network. The cause of this accident were the combined effects of heavy rainfall and a poor design of the tailing dam in the Mailuu-Suu catchment [46; 51].