While Eichler homes were obviously not built to the same earthquake safety standards as current code requires, they did use foundation bolts in the exterior walls. An easy improvement is to remove the original small washers and replace them with larger, and thicker, square or rectangular washers that will reduce the likelihood of the sill plate rising up off the bolt during a major quake. In the photo at the right, the original (and laughably inadequate) washer is shown on the slab, and the new washer is installed. In some cases I found that the bolt was too close to a stud to accept a new washer, but I was able to do this switch for most of the bolts.
However, the original bolts were not placed with consistent spacing, so I had the contractor add new bolts, secured with expoxy, in a dozen locations around the house (shown below). This is not expensive, and in my opinion well worth doing if you have your walls open.
The other earthquake safety-related changes that were done were replacing all the original single-pane untempered glass with dual-pane safety glass and adding "shear wall" bracing: 3/4" plywood panels, cross-nailed, covering the interior surface of three walls of the house.
Foundation Bolt Washers 13 