Sound waves are longitudinal waves that must pass through a medium.
Ultrasound waves have a frequency above the normal range of human hearing. They can be used to scan for birth defects in unborn babies and for defects in manufactured equipment. They can also be used to clean delicate equipment without the need to take it apart.
Seismic waves travel through the Earth. There are two types - P waves and S waves. They have different properties and they can give scientists information about the Earth's structure.
[ This page has been adapted from www.bbc.co.uk/schools/gcsebitesize/science