## 4 Results  
We mainly discussed the operation results of three groups of different extensional rate models, their evolution process, and the time of rupture. The original simulation results of the three models (Figures 5-7) were interpreted, and the major faults were marked. In addition, the bulk strain (Figure 8) and viscosity field (Figure 9) changes in models 1 and 2 were compared. Figure 5: Original simulation results (left) and interpretation (right) of Model 1. Figure 6: Original simulation results (left) and interpretation (right) of Model 2. Figure 7: Original simulation results (left) and interpretation (right) of Model 3. Model 1:  
In Model 1, the extension rate was fast enough (half-extension rate = 30 mm/a) that, during the initial rift, the lithosphere was thinned rapidly and the mantle upwelled rapidly, heating the lower crust above the Moho temperature and significantly reducing the layer viscosity. Low viscosity in the lower crust led to the decoupling of the mantle and crust, deflecting the mantle upwelling, with the highest heat flux deflected to one margin. The lithospheric mantle continued to thin in the stress concentration area, and the crust was pulled apart before the lithospheric mantle to form the ocean basin (Figure 5). The model presented asymmetric expansion, and the expansion center was closer to the left side of the model, in the area between 200 and 300 km to the left side. Meanwhile, the faults on the left side of the model were relatively dense and large detachment faults, while only a few large normal faults occurred on the right side. It only took 4 Ma from rift development to crustal rupture, which was a short time involving rapid structural development. In general, the simulation results of Model 1 had a high degree of fitting with profile AA' in Figure 2. The AA' profile exhibits asymmetric spreading, with the size and number of fractures on the northern margin being greater than on the southern. The crustal thickness of the northern margin is slightly greater than that of the southern margin, while the thickness of the lithospheric mantle is smaller in the north than in the south. The results obtained from the simulation of Model 1 are similar to the actual profile, both in terms of the distribution of fractures and the morphology of the crust and lithospheric mantle. Model 1 can initially correspond to the spreading patterns of the NWSB and the ESB. Figure 8: Bulk strain of the simulation results. Model 2:  
Model 2 (Figure 6) presented approximately symmetrical spreading, with the spreading center in the center of the model, and the lithospheric mantle and crust fracture occurring almost simultaneously. The resulting faults were mostly concentrated near the spreading center of the model and are symmetrical normal faults. Compared with Model 1, Model 2 had a slower thinning rate, a longer time to reach the final rupture, and a more uniform lithospheric thinning. The faults in Model 2 were smaller in size and did not develop detachment faults, and the geological structure is relatively simpler. Model 3:  
Model 3 (Figure 7) was set up to test the opinion that the SWSB possessed a very slow spreading rate. According to the simulation results, it was found that the lithosphere thinned slowly, and a large number of high-angle normal faults appeared in the model under the condition of a half-extension rate of 12.5 mm/a and formed a nearly symmetrical rift basin. After the model was run for 7.44 Ma, the crust and lithospheric mantle still did not break up, and the thickness of the crust remained large (>10 km), so it was difficult to rupture and form an ocean basin in a short time. The BB' profile (Figure 2b), the spreading of the southwestern sub-basin, shows nearly symmetrical spreading, with large disruptive faults cutting through the crust and more intense ruptures, and the upper crust of the northern margin has suffered more damage and has thicker sediments than the upper crust of the southern margin.