Ground motion, or shaking, is the vibration that occurs from movement of the soils due to displacement along earthquake faults. Geologists generally consider strong ground motion as the shaking that occurs near the causative fault. The ground motion at a particular site is dependent upon several factors:
- The strength, or magnitude of the earthquake,
- The distance from the fault,
- The type of soils located beneath the site, and
- Other effects such as wave channeling or local phenomena
The USGS has recently produced peak ground acceleration maps for the United States, based on probabilities of rupture and magnitude of known faults. See http://earthquake.usgs.gov/research/hazmaps/
