In the pre-disturbance phase (𝑇 ∈ [0, 𝑇 0 ]), system performance fluctuates within the safety zone until the primary hazard occurs at 𝑇 0 . The primary hazard could be the onset of random failures or Na-tech events caused by one or more natural hazards. In the disturbance progress phase (𝑇 ∈ (𝑇 0 , 𝑇 2 ]), the system enters the dangerous zone.