Most earthquake retrofits have involved improving the connection of the house to the foundation. This has been accomplished through use of metal straps, anchors, bolts, lags screws and/or nails to connect the wood sole plate to the foundation. This is probably the first area that should be retrofitted when considering and earthquake upgrade. In an earthquake, a house that is not connected to the foundation has a tendency to move or ‘walk-off’ the foundation, causing severe and sometimes irreparable damage. Even if the building itself is strong enough to withstand the motion, without a good connection to the foundation the rest is pointless.
Note: Typical building codes used in the State since 1960 have had a requirement that the foundation sole plate be anchored to the foundation by ½ - inch diameter bolts space six-feet apart along the foundation wall. Depending on the type of floor construction, you may not be able to see if these bolts exist (especially in a ‘post and beam’ type floor system where the sub-floor boards or plywood are nailed directly to the sole plate, covering the top of the bolt and nut). See Structural Mitigation for information on anchorage foundations and other earthquake retrofit information.