To determine if the home has been bolted to its foundation, go into the crawl space and check for the anchor bolts coming up through the sill. If you don't see them at regular intervals, the home has not been bolted to its foundation.
Having the home bolted to its foundation, in addition to potentially saving thousands in repairs should an earthquake occur, also increases the home's value. This is not a job to do yourself. It must be done by a licensed contractor. The cost for foundation bolting ranges from $250 to $5,000.
Costs vary greatly by region (and even by zip code). To get free estimates from local contractors, please indicate yours.