The seismic wave that arrives at the surface first and moves by compressing and expanding the ground like an accordion is the P-wave, or primary wave.

Here's why:

* P-waves are compressional waves: They travel by squeezing and stretching the material they pass through, much like pushing and pulling on an accordion.

* Fastest travel speed: P-waves are the fastest type of seismic wave, which is why they arrive first at a seismograph.

* Can travel through solids, liquids, and gases: This makes them different from S-waves, which can only travel through solids.

Let me know if you'd like more details about seismic waves!