## 3 Results and Discussion
### Overall Interpretations of the Results of Baseline Case

Table 4: The timeline of Baseline Case. Figure 5 presents the recorded data from the wave gauges, accelerometers, piezometers, and the microphone. Figure 5a shows the water level in the flume, and by calculating the water level in the flume, the water level in the flume, and the water level in the flume. Figure 4: Series front side images of the slope model from Stage 1 to Stage 3. (**a–e**) Stage 1; (**f–j**) Stage 2; (**k–o**) Stage 3.  
the amplitude of the water level, the significant wave heights \(\rm H_{s}\) for Stage 1, Stage 2, and Stage 3 were found to be 1.75 cm, 2.29 cm, and 4.7 cm, respectively. Figure 5a shows that the water level changes were stable during Stage 1 and Stage 2. However, there was a significant change in the water level amplitude during Stage 3. This might be due to the changes in the slope profile; that is, the changes in the slope profile affected the location of wave reflection. The interaction between incident and reflected waves could have caused resonance phenomena, leading to an increase in wave amplitude during Stage 3. Figure 5: Original data: (**a**) wave water level, WL1; (**b–d**) acceleration, Acc1\(\sim\)Acc 3; (**e**) sound pressure, Mic; (**f-i**) pore pressure, PP1–PP4 (the amplitude of Acc 1 during Stage 3 is out of range due to Acc 1 being exposed on the slope surface). In general, coastal erosion processes could involve erosion, block falls and mass movements, etc. Usually, wave erosion could first induce undercutting of coastal slope toes near sea level, then trigger block falls if vertical joints are formed due to gravity or even trigger large-scale mass movements when deeper-seated rupture surfaces further developed. These different types of erosion processes could happen in no particular order. Wave erosion occurs mostly within the range of wave swash, while mass movements can occur from the wave swash zone up to the top of the slope. Block falls may occur when the slope within the wave swash zone becomes flatter and the slope above the wave action zone becomes steeper, resulting in a steep cliff profile. Two primary causes may lead to mass movements. (1) The periodic action of waves and backwash creates fluctuations in pore pressure within the slope, gradually weakening its structure and increasing the likelihood of sliding. (2) Swash and backwash can erode the slope's surface, resulting in the formation of a wave-cut notch, which further compromises the support for the slope above the notch, ultimately triggering a large-scale slope failure. Taking the Baseline Case as an example, during the initial stage of erosion, the slope within the wave swash zone is steep, and the primary type of slope failure is sliding. This causes materials to move downslope into the wave swash zone, where they are eroded by the waves (Figure 4a-l). Swash and backwash formed a wave-cut notch on the slope surface (Figure 4c). As the waves continuously act on the slope, their angle within the swash zone gradually becomes less steep and flatter, while the slope above the swash zone begins to develop a steep cliff profile (Figure 4l-o). At this stage, block falls occurred. Figure 5b-d show the seismic signals from accelerometers Acc 1-3. Figure 5b-d indicate that as the wave height increases, the amplitude of the seismic signals also increases, as seen from Stage 1 to Stage 2, and increases significantly in Stage 3. By comparing the acceleration amplitude of Stage 3 in Figure 5b-d, we learn that the closer the accelerometer is installed to the slope face, the higher the amplitude it records. Additionally, the amplitude difference between Stage 2 and Stage 3 of Acc 1 (Figure 5b) is much higher than that between Stage 2 and 3 of Acc 2 (Figure 5c), also due to Acc 1 being installed closer to the slope face than Acc 2. Similarly, the phenomenon still exists when comparing the amplitudes of Acc 2 and Acc 3. It can be seen that the closer the monitoring position is to the slope, the more obvious the difference in the amplitude of seismic signals caused by different wave erosions.