Earthquake is the threat, not the problem. Like snowstorms, tornados, hurricanes, wildfires, and so on, the threat helps you understand the potential problems.
Off the top of my head:
- First responders saturated
- Utilities down
- Definitive medical care saturated
- Damage to your home
- Neighbors needing help
- Local security issues
If you’re ready to solve the problems that are likely to come up, the source of the problem becomes less of a preparedness issue, IMO.
Where I live, I’ve put some effort into being ready to solve all of those problems for myself, my family, and in a limited fashion my neighborhood, for a reasonable period of time. “Bug in” is our default unless our house has been significantly damaged or the outages go beyond our capacity to handle them.