Hi,
I just finished working on a new house next door. They did a complete teardown as the old foundation had NO steel in it. This is why many do a scraper and all new construction. Todays code requires bolts in the foundation to be attached to 4x4 studs, wall supports, thus holding the actual wall frame to the foundation. It is part of what is called a sheer wall. Makes the house sound and prevents some of the vibrations such as the house shaking when the door slams. The other requirement is to cover these sections in plywood nailed every 6 inches. Makes a strong wall. If you were to stay because you liked the house, you could remove the wall covering on the outside and sheet the walls in plywood. Some interior walls would also need to be done with plywood. Would make a stronger house and it would shake less. Could be very expensive and would require a structural engineer to design it.

This is why remodling older homes becomes a problem. The old system of bolting a house to the foundation is really a joke. With no steel in the older foundations they just break apart or the bolts pull through the wood sill (wooden board the floor supports are nailed to). To retrofit an old home, the best way is to uncover the outside walls and strap them well past the sill and bolt the lower end to the concrete foundation, again a very expensive job. If you buy a home, it pays to have a good inspector look at it and don't be afraid to ask hard questions. Knowing your geology and that of the area does not hurt either.

Oh yes, get earthquake insurance also!
Bob in Woodland Hills
PS My house shakes some and made it through the Northridge quake very nicely. In part becaue it did move to some degree. Not sure about the next one though???