Earthquake waves can be either transverse or longitudinal. if an earthquake wave is moving to the east, and the ground is moving back and forth along the east-west axis, this is a wave.

The answer is Longitudinal waves. 

The particle displacement in a longitudinal wave is parallel to the direction of wave propagation. The ground particles simply oscillate back and forth their equilibrium positions unlike transverse waves that do not move along with the waves but rather oscillate up and down their individual equilibrium positions.

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