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

Here's why:

* P-waves are compressional waves, meaning they travel by squeezing and stretching the material they pass through. This back-and-forth motion is similar to how an accordion works, hence the analogy.

* P-waves are the fastest type of seismic wave, which is why they arrive first at a seismograph. They can travel through both solids and liquids.

Let me know if you have more questions about seismic waves!