Final answer:
The P wave arrives first at a seismometer after an earthquake.
Step-by-step explanation:
The type of seismic wave that arrives first at a seismometer after an earthquake is the P wave. P waves, also known as primary waves, are the fastest seismic waves and can travel through solids and liquids. They cause the ground to move back and forth in the direction of the wave's propagation.
Learn more about Seismic waves