Hi Michael. Try to view the fault in 3 dimensions and not as a line on a map. The top of the fault can be in one location while the bottom of the fault can be in another location.

This is the case with the Rodgers Creek fault. I can stand on top of the fault, but the bottom is a few miles to the east as the fault goes down at about a 70 degree angle to the east. I don’t know in fact if the whole fault does that, but I do know in the areas where they have had some quakes the angle is about 70 degrees.

Not knowing where the bottom of the Great Valley Thrust fault is I think it most likely occurred on the fault. Take Care…Don in creepy town.