The seismic waves that arrive at the surface first and move by compressing and expanding the ground like an accordion are called P-waves or primary waves.

Here's why:

* P-waves stand for primary waves because they are the fastest type of seismic waves.

* They travel through both solids and liquids, and their motion is similar to sound waves, where particles oscillate back and forth in the same direction as the wave travels. This compression and expansion motion is what gives them the "accordion" analogy.

Let me know if you have any other questions about seismic waves!