This was posted to another list I'm on and I find it rather interesting...

"A vast chunk of Earth sliding under Mexico has surprisingly reversed direction, puzzling geologists and leaving them wondering whether the ground might be poised to pummel Mexico City with a devastating earthquake."
(rest of article at: http://www.livescience.com/environment/070802_fault_backward.html )

The article also mentions this has been seen in the Cascadia area - both areas are what's left of the Farallon plate - it surely makes one wonder what might be happening (if anything)under the california and basin/range area since this was all once the Farallon plate ...

Canie

• In Surprise, Major Earthquake Fault Slips Backward