I live in the red clay area of Tennessee on a ridge.We have FELT several earth quakes that have caused hairline cracks in are basement walls, and in the brick pillars of our porch. I don't believe this is due to trust lift,settling, or clay freeze /thaw under the foundation. I built our home with a lot of structural rebar in the foundation and 12 inch block walls, the standard is 8 inch walls. I have seen multi cracks appear in my house and my garage/apartment (in separate location) over the pass 7 years. My insurance says they don't carry earth quake policies,I feel more research needs to be done on this fault zone.