Saturday, March 8, 2014
The great OK fault model - thrust
Here we have a few from above. Don't forget that the main lines are trending NE towards Toronto. All the stress is down this trend, so you can't have a good earthquake without a break. Although the last movement of the megathrust was downwards, the plane of the megathrust just acts as a weakness.
The weakness that gives us a New Madrid is a transform, or adjustment fault. The old mountain ranges weren't perfectly straight. Where there was a curve, or a change in strength, you got a crack. Wasn't much movement, but it became a weakness. The intersection of the two faults is an essential thing to get a growing fault mechanism.