Earthquake Retrofit Services reprinted courtesy of ServiceMagic

1. Cripple wall failure.

This occurs in older wood-frame houses on taller crawl space walls. Taller crawl-space walls are also known as cripple walls; they are built with vertical 2X studs. They can be found between the foundation and the floor joists. Even in some of the recent minor quakes, such homes have been destroyed when these walls collapsed.

Un-reinforced cripple walls are a weak link for getting the earthquake loads from the lower floor to the foundation. Plywood reinforcement on the inside face of the cripple-wall studs can save a house from destruction in a future quake. It's a cheap fix, and neglecting it is foolhardy.

Shear failure happens when the bottom of a building moves under the force of a quake but the top doesn't.

2. Sliding failure.

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