## 3 Microseismic Evolution Characteristics of Rockburst Formation Process
### Special Types of Rockbursts
#### 3.3.2 Delayed Rockburst  
A delayed rockburst refers to rockbursts that occur outside the range of stress adjustment and has discontinuous microseismicity after excavation and unloading [41]. Because of the uncertainty in its occurrence time and location, it is difficult to provide an accurate early warning for delayed rockbursts, posing significant safety risks to construction personnel and equipment. So far, research on the time effect of delayed rockbursts and rock failure is lacking. In terms of engineering research, [PERSON] [48], [PERSON] and [PERSON] [49] observed that the microseismicity of hard rocks and the fracture process of the rock mass in high-stress areas are related to the time behavior of the stress migration process, which affects the long-term stability of the tunnel. [PERSON] and [PERSON] [50] proposed that the decrease in the rock strength under a constant stress is the condition for the formation of delayed strainbursts. [PERSON] et al. [40] compared the microseismicity in the evolution process of delayed and immediate rockbursts. They observed that during the formation process of a delayed rockburst, the microseismicity gradually dominated by tensile ruptures, and before the occurrence of the delayed rockburst, the microseismicity exhibited an evident quiet period. By analyzing the intensity of the blasting disturbance and the delay time of a time-delayed rockburst, [PERSON] et al. [51] discussed the correlation between time-delayed rockbursts and blasting disturbance. [PERSON] et al. [52] observed that during the excavation of the time-delayed rockburst area, microtemors were frequent and concentrated in space, the EI remained high and had a downward trend, and the changes in the apparent volume and EI were not evident during rockburst occurrence. [PERSON] et al. [41] observed that during the formation process of a delayed rockburst, the microseismic events and the sliding displacement of the microcracks decreased gradually; however, the microseismic events with a high energy density continued to occur. The phenomenon of delayed rockbursts shows that the early warning and prevention of rockbursts should not only be limited to the rockburst near the working face, but attention should also be paid to the microseismicity behind the working face. The potential risk of a delayed rockburst can be predicted by comparing with the microseismic evolution law of existing delayed rockbursts. In the laboratory test, [PERSON] et al. [53] conducted a triaxial unloading test on sandstone, keeping the axial stress level unchanged and unloading with different confining pressure until failure. The results showed that, the higher the degree of unloading, the shorter the time delay of failure. Based on the results of a triaxial creep test on diabase in the dam foundation of Dagangshan Hydropower Station, [PERSON] et al. [54] established an evolution equation for the nonlinear creep damage of the rock mass therein. It reflects the entire process whereby the damage increases with time and leads to the failure of the rock mass. [PERSON] et al. [55] studied the time-dependent behavior of creep failure through triaxial