The basic rectangular, single-story, wood-frame house is one of the safest types of structures in an earthquake. The amount of damage incurred should be minimal if the house is properly engineered and built. The key to a well-designed building is its ability to withstand an earthquake as a single unit.

Houses built on steep hillsides, or with split levels, second stories over garages, pole foundation systems, cripple walls higher than 4 ft., too many windows, or irregular features, can represent greater risks. In such situations, a structural engineer should be consulted.

The shaking and lateral forces of an earthquake will separate building components at their weakest points. Therefore, all structural elements must be securely tied together: The structure must be tied to the foundation with anchor bolts to keep it from sliding; the wall studs must be sheathed (tied) with plywood or some other material to reduce deflection and provide strength; and the floors and roof must be fastened securely to the walls to tie the structure together. Almost all existing structures can be strengthened to be more earthquake-resistant (but not earthquake-proof).

Masonry chimneys should be reinforced with steel and tied to the roof and upper floor framing with steel straps to make them more earthquake-resistant. Unreinforced masonry chimneys should either be removed and replaced with a properly braced metal flue and enclosure system (that is, wood-frame), or measures should be taken to mitigate the effects of potential damage.

Clay and concrete tile roofs can weigh five to 10 times as much as lighter roof systems, such as composition shingles. The increased weight results in significantly larger earthquake loads for the roof and walls. Heavy new roofing should not be added to existing structures without consulting a structural engineer.

There is a 70 percent chance that you and your family will be at home during the next earthquake. You have a choice as to how well your home will perform.