Distribution and characteristics of loess landslides triggered by the 1920 Haiyuan Earthquake, Northwest of China

On December 16, 1920, an earthquake with a magnitude of 8.5 occurred in Haiyuan County, Ningxia Hui Autonomous Region, Northwest of China. This earthquake triggered several thousand loess landslides which resulted in thousands of deaths and blockages of rivers. The distribution and characteristics of the landslides triggered by the Haiyuan Earthquake in loess areas were studied using satellite images and field investigation. A total of about 3700 landslides with a cumulative area of about 177 km2 were interpreted over an area of 21,000 km2. It was found that landslides triggered by the earthquake were concentrated in a western of 40-55 km from the Haiyuan fault. Landslides were concentrated near ridge crests, with 65.7% of the landslides originating in the upper quadrant of slopes. The aspects of the landslides triggered by the Haiyuan Earthquake were parallel to the faults and there is no back-direction effect in landslides triggered by Haiyuan earthquake. These landslides have long run-out distances(travel distance (L)/height different (H) > 0.6) and deposited materials in river channels, forming 51 dammed lakes that still exist. The relationship between the area (A) and volume (V) of the landslides is V = 4.170 × A1.086. Based on the relationship between number and volume of landslide and the magnitude of earthquake, >100,000 landslides with a cumulative volume of 0.5 × 1010 m3 were triggered by the Haiyuan Earthquake. As loess is sensitive to liquefaction during an earthquake and tends to produce landslides with long travel distances. Hence, the loess depth, slope and geological stresses are the primary factors responsible for the high density of landslides in this region.