*4.1. Sliding Source Area (Area I)*

The sliding body was mainly Quaternary loess. There were many cracks in the upper part of the trailing edge, the crack width ranged from 23 to 54 cm, and there was an unstable body in the upper part of the trailing edge. Its volume reached 1.2 <sup>×</sup> 104 m3. The average width of the sliding source area was 73 m. The area was about 1.2 <sup>×</sup> <sup>10</sup><sup>4</sup> <sup>m</sup>2, the average thickness of the sliding body was 4–7 m, and the volume was about 5.0 <sup>×</sup> 104 <sup>m</sup>3.
