Part of the problem in PR is their being an island makes the logistics of getting stuff to them harder. Part is they had not maintained their infrastructure. Part is a bloated dysfunctional govt that cannot do anything quickly or efficiently.
GS is right that something like a New Madrid earthquake would change things quickly on the mainland, not just from the immediate damage, but also from the disruption of bridges and utility/communications/energy infrastructure over the Mississippi coming down cutting East-West transport and links.
This past weekend I was on Long Island for an annual event, this time further out on the island than I normally go. The sprawl is endless and there are not even remotely enough resources to sustain the population if the daily fleet of supply trucks didn’t come. I doubt many there realize just how trapped they are. Other than private boats and a few ferries, there is no way to get off the island except going through NYC. Long Island has about 8 million people. There’s almost 9 million more in NYC itself with another million each in Westchester County, NY and Fairfield County, CT plus 6 million in NYC’s sprawl in Northern NJ. Yet few on Long Island realize just how precarious their position is in a major SHTF event. I am always glad when I get north of Westchester County again on my way home.