P and S waves

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





P waves – primary, push – longitudinal waves. These 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 – secondary, shake – 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.

Low- density crust – 2800 kgm^-3, high-density mantle – 3300 kgm^-3.
Average density of the Earth = 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.