S and P Waves

You will need to know about body waves, as they tell us so much about what we cannot see inside the planet.

P-waves

Primary waves are longitudinal waves that push and pull the earth. They are the fastest body wave, averaging speeds of about 6 km/s, so arrive first.

Secondary waves are transverse waves, which make the earth shake from side to side. Slower than P waves, they average about 4 km/s so arrive second.