GLG 301 Lecture Notes - Lecture 22: Seismic Moment, Rise Time, Teleseism
Document Summary
What is it about shaking that causes damage: specific response of structures to shaking is very complicated, ground motion. How fast does the ground motion change (m/sec2) Analogy if you are on a rug and it is pulled, you can stand on it if pulled gently; if it is jerked quickly, you fall: shaking direction and distance. Structures are generally weaker to horizontal shaking than vertical motion. Buildings vibrate at characteristic frequencies which are related to their height (and other things). A first approximation resonance frequency is 0. 1 x number of stories in the building. If the vibrations of the ground is close to the natural frequency of the building, they are said to be in resonance with each other. Resonance amplifies the response of the building, creating more damage. On the other hand, taller buildings that are more flexible might bend a bit during an earthquake, while short buildings might be stiffer and break: ground conditions.
