Imagine a major winter windstorm. The primary disruption is to the electrical system. Falling trees break powerlines and that often causes failures at smaller distribution substations, resulting in widespread outages. Often hundreds of thousands of residents and businesses are without power for a day or more. The effects of windstorms on lifeline systems are fairly easy to visualize.
Earthquakes present a more complex challenge.
First, lifelines are dependent on many components operating together to make the system functional. Failure of one critical component can bring down the entire system. Second, earthquakes tend to effect many lifeline systems at once. Failures in the highway system may make restoration of a critical electrical power substation or sewer treatment plant more difficult. Third, earthquakes can cause significant failure of structures such as bridges that are not quickly or easily replaced.