Complexity of the Precambrian
The wonderful Precambrian runs under the whole eastern half of North America, yet the usgus knows nothing about it. That's because it only outcrops in Canada. There's a bit on the East Coast, but that's weird stuff, sliced up and over-thrusted in the Appalachian mountain building.
The pc (nothing to do with Harper) contains the only quartz in the region, and thus is the source of earthquakes. This is the same in California, where the deep quartz is involved in earthquakes, and not the mapped surface slop. They only figured this out recently with deep San Andreas drilling.
I've written tons on this complex structure. Just visualize huge mountain ranges like the Rockies, and rock underneath. Unfortunately, the hidden model for the usgus and nuclear waste disposal is that the whole thing is a slab of featureless tombstone granite. For earthquakes, the important features are a series of parallel megathrusts running down in a NE-SW direction, and associated NW (perpendicular) adjustment faults.
According to all the deep seismic tomography, NA has spread and settled into a cold basin (cold roots). This scrunches everything up like putting your thumb on a beachball. We should have uniform high horizontal stress, but proof that the megathrusts have reactivated is the fact that our deep horizontal stress is highly polarized in the NE direction. I remember that our deep hole at Darlington was so polarized that the fracking stress measurements were suspect. Suffice to say that deep mining has encountered these stresses and they are magnificent.
The usgus thinks the stresses dominating OK are E-W. That's fine.
-to be continued with the final section on stress corrosion.