# Factors Affecting the Stability of Loess Landslides: A Review
## 2 Relevant Measured Parameters
### Parameters of Landslide Structures  
The internal structure of loess landslides has been investigated and validated using a variety of methods. These include porosity analysis [34; 35; 36; 37], fracture structure assessment [8; 15; 38; 39; 40], landslide geometry evaluation [4; 8; 36], and investigation of subsurface geological conditions [8; 15; 17; 22; 23]. The techniques used include electrical testing [8; 20; 23; 30; 34; 36], seismic testing [35; 41; 42; 43; 44; 45; 46; 47; 48; 49; 50; 51; 52; 53], mechanical testing [13; 14; 15; 18; 19; 22; 37; 38], and borehole data analysis [9; 31; 43; 47; 53; 54]. Figure 1 shows the vertical and lateral structure of landslides in the Heifangtai terrace [55]. Geological hazards, such as landslides, avalanches, and collapses, can occur due to the presence of joints in loessess [4; 38]. Volume contraction, or the tendency of the soil to contract under different stress paths due to the destruction of the loess structure, has been suggested as a mechanism for the stress-induced failure of loess landslides [56]. It has been found that clustering occurs as a result of the inherent structure of loesses, summarizing the general characteristics of landslides on the Loess Plateau. In particular, it is susceptible to collapse under high pressure due to its loose composition and high porosity. The volume, length, width, and thickness of the deposit, vertical difference, sliding direction, slope angle, and dip of the strata are of great importance in landslide structures [57].  
Seismic methods have been extensively investigated by academic researchers in various countries, including the use of seismic refraction tomography (SRT) for the determination of stratigraphic thickness variations in landslides [41; 43; 45; 47; 48; 51; 52; 58], seismic scatter imaging (SSI) to characterize the interior of landslides [47; 58], horizontal-to-vertical spectral ratio (HVSR), and multichannel analysis of surface waves (MASW) to analyze the spatial distribution of subsurface structures [43; 49; 50]. In addition, the use of ERT for the determination of water content distribution within the landslide and the geometry of the landslide surface [43; 44; 45; 46; 47; 48; 52; 58] and ground penetrating radar (GPR) for the analysis of the spatial stratigraphy of the landslide [3; 31; 44] are commonly used in electrical methods. To provide a thorough understanding of the complexity of the subsurface, these methods are often calibrated using borehole data. This approach allows the investigation of fracture systems in loess landslides, reconstruction of landslide topography and geometry, study of fracture-water interactions, analysis of complex subsurface geological conditions, mapping of landslide surfaces and failure surfaces, assessment of changes in landslide thickness, and identification of paleochannels, landslides, and failures [8; 9]. It also assists in the confirmation of changes in the internal structure of landslides, the identification of the depths of major landslide surfaces, the analysis of landslide evolution, and the development of hydrogeological models for landslide events [41; 42; 43; 44; 45; 46; 47; 48; 49; 50; 51; 52; 53]. It can also be used to differentiate loess landslides, as shown in Figure 2 regarding the differentiation of rock landslides by