Why is ground acceleration gives the best measurement for earthquake intensity?

Ground acceleration gives the best measurement for earthquake intensity because the acceleration contains both the magnitude of an earthquake and its frequency contents.

An earthquake is a disturbance in the earth’s crust. It creates energy waves that ripple out in all directions. These waves are sudden, rapid like a jolt when they reach the earth’s surface. Though the overall displacement at the earth’s surface due to an earthquake is small, the sudden change in displacement will have high acceleration. The force induced on the buildings due to ground motion is proportional to the ground acceleration.

In summary, measuring the earthquake acceleration provides the following valuable information.

1. Measurement: Sophisticated seismometers measure acceleration directly. Velocity and displacement need integration of acceleration that may have mathematical errors.
2. Rich in content: Acceleration contains amplitude (i.e., how much is ground motion) and how quickly it changes direction (frequency). The velocity peak in a wave does not represent the direction of movement but the acceleration peak represents the direction of movement. Hence the acceleration reveals the frequency content.
3. Engineering Analysis: The ground acceleration due to earthquakes is proportional to the induced force in the buildings. The stresses and strain induced in the building structure can be found from these forces.