Interesting that you say that, because there just happens to be a huge fault line that travels along the length of the Mississippi River.

When Matthew Bracken wrote about huge recurring earthquakes along the Mississippi River in his third book in the Enemies series, Foreign Enemies and Traitors, he wasn't just making stuff up. That could indeed happen.

According to most American Indian lore, North America is a giant turtle with dirt covering its back. There also happens to be a Mohawk belief that some day this turtle's back will break, right down the middle. The Indian metaphors are obvious.

However, I still believe this was an act of sabotage. Oil rigs elsewhere in the world are highly secure, however right off the US coast, security (if it exists at all) is nowhere near as tight. A saboteur who knows his way around oil rigs could easily pull this off.