There are a number of important characteristics common to all buildings which further affect and complicate a building's response in terms of the accelerations it undergoes, and the deformations and damages that it suffers. When these are near or equal to one another, the building's response reaches a peak level. In some circumstances, this dynamic amplification effect can increase the building acceleration to a value two times or more that of the ground acceleration at the base of the building. Generally, buildings with higher natural frequencies, and a short natural period, tend to suffer higher accelerations but smaller displacement. The taller a building, the longer its natural period tends to be.
Taller buildings tend to be more flexible than short buildings.
If it is very short, it is difficulty to bend it in your hand. If the rod is somewhat longer, and of the same diameter, it becomes much easier to bend. We say that a short building is a stiff, while a taller building is flexible. Stiffness greatly affects the building's uptake of earthquake generated force. Reconsider our first example above, of the rigid stone block deeply founded in the soil.