A strip foundation is a shallow linear foundation that supports load-bearing structures such as walls. This type of foundation shifts deformation constantly and is therefore very stable during an earthquake.
A foundation transfers the load from a structure to the ground beneath it. As a precautionary measure, a stable foundation needs to have more than enough strength to support its projected maximum load. It also needs to withstand changes in the ground beneath it even if these changes result in asymmetrical deformation. A shallow foundation, such as the strip foundation, needs durable and stable soil to support it.
In a normal state, the soil stress on a strip foundation is distributed symmetrically and is greater near the load-bearing columns. During an earthquake, the majority of stress shifts to one edge of a strip foundation, while the other edge loses stress. Since the stress caused by an earthquake is large and pointing upward, the bottom part of the strip foundation must have extra reinforcement to compensate. However, since the deformation on a strip foundation is generally changing direction and magnitude, it is also necessary to reinforce the top part of it as well. Additionally, since the load shifts to the edges of the foundation, it is efficient to have the foundation extend beyond the columns on the edges.