P and S waves

Primary and secondary – push (longitudinal) and shake (transverse)

P waves

These are primary waves. They push and are longitudinal waves. They move rapidly and can pass through both solids and liquids. You can compare this with pushing the end of a line of dominoes – they all fall down.

S waves

These are secondary waves. They arrive at a point after the P waves. they shake the ground and are transverse waves. These move less rapidly and hence the name secondary waves. They can only pass through solids. You can compare this with pushing the domino sideways – the others are not affected.
Double shock felt in some areas – P first then S.

The Earth has a low- density crust – 2800 kgm^-3, and a high-density mantle – 3300 kgm^-3.
The average density of the Earth being 5527 kgm^-3.

Richter scale of earthquakes – 1958

4 Hanging objects swing. Wooden walls and frames creak
5 Felt outdoors
6 Felt by all. Many frightened and run out doors. Trees and bushes are shaken visibly and heard to rustle
7 Difficult to stand. Damage to masonry.
8 Partial collapse.
9 General panic. Masonry heavily damaged. General damage to foundations. Buildings collapse.