## 2 Development of Seismic Resilience of Modern Urban Communities
### Research on Seismic Resilience of Modern CISs
#### 2.2.2 Seismic Resilience of Interdependent CISs  
In the early 2000s, a series of unprecedented cascading failures of CISs on a global scale prompted renewed research into their hidden vulnerabilities ([PERSON] et al., 2019; [PERSON] et al., 2020; [PERSON] et al., 2020; [PERSON] et al., 2020). These systems, which play critical roles in various domains, exhibited a significant lack of resilience even when faced with seemingly minor initial disruptions. Researchers turned to complexity theory to revisit the behaviour of these CISs. The findings consistently pointed to the inherent vulnerability of modern CISs, stemming from their intricate intra and interdependencies. These dependencies create a delicate balance, making the systems susceptible to failures ([PERSON] et al., 2019; [PERSON] et al., 2020; [PERSON] et al., 2020).  
The CIS vulnerability induced by interdependencies also extends into real-world hazard events, such as destructive earthquakes. To safeguard the resilience of modern urban communities, it is imperative to deepen understanding of these vulnerabilities and actively work toward effective mitigation strategies.  
[PERSON] et al. [67] conducted a comprehensive study on EPSS resilience under two significant real-world earthquake events: the 2011 M\({}_{\text{W}}\) 9.0 Tohoku earthquake in Japan and the 2010 M\({}_{\text{W}}\) 8.8 Maule offshore earthquake in Chile. Their research specifically investigated the interdependencies between EPSSs and telecommunication systems. To that end, this study analysed time series data related to damage, outages, and service restoration of both the two CISs throughout the respective earthquakes. The findings revealed a strong coupling between the restoration of the EPSS and telecommunication systems in both Japan and Chile. In particular, the restoration of mobile communication networks was more closely tied to EPSS restoration than that of landline telephony systems. This consistent pattern underscores the significant and asymmetric dependence of telecommunication systems on EPSSs. Consequently, the study highlights the urgent need for innovative technological solutions, such as microgrids, to enhance the resilience of telecommunication systems and safeguard the entire community under catastrophic earthquakes.  
It is noteworthy that modern CISs exhibit interdependencies that extend beyond the conventional, \"unidirectional\" relationships. Both the operation and post-shock recovery of CISs are often mutually reliant, as observed under real-world scenarios [6]. Researchers have begun investigating the impact of this looped interdependence on CIS resilience. In a recent study, [PERSON] and [PERSON] [26] explored the resilience behaviour of an interwoven system comprising an EPSS and a TS, as well as the urban community that they serve, under seismic hazards. Following damaging earthquakes, the restoration of EPSSs becomes contingent upon the functionality of TSs. Specifically, EPSS components can only be repairable if accessible via the TS; conversely, the restoration of TS is also reshaped by the time-varying functionality of EPSSs, as many TS repair equipment rely on the energy supply. To model these complex and dynamic interactions between the two CISs, an agent-based model (ABM) was developed. This ABM incorporates two key agents: the operators responsible for the recovery campaigns of the TS and the EPSS. Sensitivity analysis was run to explore how post-shock recovery is influenced by the looped interdependence between these two systems, considering various earthquake scenarios. The simulation outcome reveals a nonlinear relationship between the degree of interdependence and system-level resilience, particularly under strong shocks. When the interdependence degree surpasses a critical threshold, the resilience of the EPSS-TS-community system undergoes a sharp deterioration, especially when viewed from a societal perspective.