Could earthquakes on San Andreas Fault be stopped by driving huge steel piles deep into bedrock on either side of fault and welding huge cross beams, thereby anchoring ever north moving Pacific Plate to more stable North American Plate?

No.

Imagine you are floating a large thin cookie on a lake of milk.

When you went to move the cookie it fractured.

For some reason, you decided to mend the fracture using staples. Now remember, you’re really good at mending cookies with staples, so it is a good fix.

The problem is that when you go to move the cookie again it will likely fracture just outside the mending. And that assumes the mending was strong enough in the first place.

Compared to the forces exerted on the cookie the mend will never be strong enough because the cookie isn’t strong enough to resist the forces.

Hopefully, my analogy makes sense. I’m going for a snack!