One of the most common causes of damage to houses in an earthquake is when they slide off their foundation. Before 1940, houses were built to just rest on their foundation and the shaking produced by an earthquake can cause them to slip off. A simple procedure whereby bolts are used to secure the house to its foundation can prevent this major cause of damage. Houses built since the 1940s are all bolted to their foundations. Older houses can be bolted now, a move that may save your house from destruction in the next earthquake. In some cases, it is worthwhile to add bolts to a newer house where the bolts are short or sparsely placed.