Ground shaking

Ground shaking from earthquakes can collapse buildings and bridges, disrupt gas, electric, and telephone service, and sometimes trigger landslides, avalanches, flash floods, fires, and huge, destructive, seismic sea waves called tsunamis.
An earthquake is a sudden movement of the Earth caused by the abrupt release of energy that has accumulated over a long time.
Objective is to estimate the ground shaking from a specified earthquake, sometimes called a scenario earthquake.In seismic design, characteristics of the maximum ground shaking are desired.
For hundreds of millions of years, the forces of plate tectonics have shaped the earth as the huge plates that form the surface move slowly over, under, past, and away from each other.
The ground shakes or vibrates as the seismic waves cause small temporary displacements of the ground.At the surface, the ground moves vertically up and down and horizontally back and forth.The strength and frequency of seismic waves and the length of time strong shaking lasts all affect the amount of damage caused by ground shaking.
When an earthquake occurs in a populated area, it may cause deaths and injuries and extensive property damage. Buildings with foundations resting on unconsolidated landfill and other unstable soils are at increased risk of damage. The effects of earthquake ground shaking depend on the specific response characteristics of the type of structural system used.
Ground shaking may also trigger soil liquefaction, landslides, and other types of ground failure, which can also cause damage.
Initial effects of an earthquake are violent ground motions which can produce cracks or fractures in the ground and liquefaction, where loose sandy soils with a high moisture content separate and give the surface a consistency much like that of quicksand.