Earthquake can easily cause cascading failures across energy systems in integrated energy systems (IES)

which seriously threatens the reliable energy supply to end-users. After a mainshock

the subsequent aftershocks may still damage the IES infrastructures

and then reduce the IES resilience

while the existing IES resilience assessment methods rarely regards the influence of the aftershocks. To cope with this issue

this paper proposes an operational resilience assessment approach for IES in the scenario of mainshock-aftershock by using arbitrary polynomial chaos expansion (aPCE). First

a framework for evaluating the operational resilience of IES damaged in mainshock-aftershock is designed. Then

an aPCE-based load shedding model is developed to optimize the load shedding capacity by formulating the relationship between the uncertain system topology

uncertain load and optimal load shedding via the polynomial functions. Further

a combination of the proposed aPCE-based load shedding model and impact-increments-based state enumeration (IISE) method is proposed to accelerate the computational efficiency of IES resilience by reducing the computational time of optimal load shedding and the number of the high order fault scenarios. The performance of the proposed operational resilience assessment with great accuracy in the approach is evaluated by IES E24-G14 and IES E118-G48 test systems. The results demonstrate that the proposed method can significantly improve the computational efficiency of IES mainshock-aftershock hazard.