Acceleration, Velocity, Displacement (Image courtesy of Charles Ammon, Penn State)

Kinemetrics FBA-23 accelerograph.

Acceleration
When you step on the accelerator in the car or put on the brakes, the car goes faster or slower. When it is changing from one speed to another, it is accelerating (faster) or decelerating (slower). This change from one speed, or velocity, to another is called acceleration. During an earthquake when the ground is shaking, it also experiences acceleration. The peak acceleration is the largest acceleration recorded by a particular station during an earthquake.

Accelerogram
A recording of the acceleration of the ground during an earthquake.

Accelerograph
An instrument that records the acceleration of the ground during an earthquake, also commonly called an accelerometer.

See also: FAQ discussion