## 3 Data and Methods
### Landslide-Influencing Parameters  
It is very important to choose the suitable influencing factors for submarine landslide assessment. There is no absolute standard parameter when classifying the hazards of submarine landslides. This issue remains one of the difficult problems in the field of research on submarine landslides. The reason is that there are too many influencing factors and it is difficult to obtain the corresponding parameters. From the point of view of geological analysis, geological factors, hydrodynamic factors, topographic factors, and human activities should be taken into account. As much information as possible should be collected to satisfy these four requirements. In this study, we have selected carefully out of all the various choices available based on the nature of submarine landslide occurrences concerning the characteristics of geology, hydrology, geomorphology, and the impact of human engineering activities. Therefore, 9 factors were selected, namely, sediment type, slope, soil strength, water depth, wave height, maximum current velocity of the bottom, liquefaction, erosion, and human engineering activities (Figure 3). The research data of the 9 factors were obtained by the First Institute of Oceanography, MNR, China through geophysical sounding, drilling, and monitoring surveys in the Chengdao sea area of the Yellow River Estuary [18], and contain detailed information on various geological features of the study area. Each factor was divided into 3 or 4 classes based on the range of data, geological background, and experts' experience in this study area. At last, 1107 points, of which longitudes vary from 118.75\({}^{\circ}\) N to 118.95\({}^{\circ}\) N, latitudes change from 38.15\({}^{\circ}\) N to 38.28\({}^{\circ}\) N, and 0.05 degrees is the interval, were selected as the research sites (Figure 1). All the data used in this study were collected from projects of the First Institute of Oceanography, MNR. Figure 3: Location map of the study area. (**a**) Sediment type; (**b**) slope angle; (**c**) soil strength; (**d**) water depth; (**e**) wave height; (**f**) current velocity; (**g**) liquefaction; (**h**) erosion; (**i**) human engineering activities; (**j**) overlay map. Sediment type plays an important role in the study of submarine landslide susceptibility, as different types of sediments have different physical and mechanical properties, which can affect the difficulty of geological disasters. Studies have shown that sediment type has a large influence on landslide stability [21]. In this study area, sediments are divided into 4 classes: silty sand, silt, silty clay, and clay. Slope angle is a significant factor in the development of submarine landslide susceptibility and the angles were calculated by the change in water depth. Slope angles are subdivided into 4 categories: <1/2000 radian, 1/2000-1/1000 radian, 1/1000-1/500 radian, and >1/500 radian. The places with large sea-bottom slopes are mainly located at 6 m and 10 m water-depth contours. Soil strength affects the stability and sliding difficulty of the submarine landslide. The greater the soil strength, the harder the slide occurs. Soil strength is divided into 0-50 kPa, 50-80 kPa, 80-110 kPa, and >110 kPa. The classification of soil strength is mainly based on data from boreholes in this study area. Water depth, which was obtained by single-beam and multibeam bathymetric instruments, can influence the strength of waves acting on the seabed. It can be classified into 4 classes: 0-5 m, 5-10 m, 10-15 m, and >15 m.  
Wave height is a very important factor because it represents the energy that a wave contains. It was collected by pressure wave and tide gauges. The wave height increases first with the depth of water, but there is no obvious increase after reaching a 9 m depth. The study area can be divided into 3 classes, which are 0.5-2.5 m, 2.5-4 m, and >4 m.  
The maximum current velocity of the bottom determines the shear stress of the current on the seabed, which may cause erosion.