The arrival and progress of an earthquake can be recognized on a seismogram by looking for the distinct P-wave and S-wave arrivals. The P-wave is the first wave to arrive and is a compressional wave that moves through the Earth's crust. The S-wave is the second wave to arrive and is a shear wave that moves through the Earth's crust. The P-wave and S-wave arrivals can be identified by their distinct shapes on the seismogram.
