Seismology
Seismology is literally the study of earthquakes (seisms) and is one of our very few methods of seeing into the deep interior of the earth. By studying the waves generated during a seismic event we can infer a great deal about the interior of the earth. In particular,
pressure (P) waves and shear (S) waves travel with different speeds through the earth (P: 5-6 km/s, S: 3-4 km/s) and will refract as they pass through regions of different density. Also, S-waves will not penetrate the earth's deep interior but will "bounce" or be refracted to either side of the core. P waves can penetrate the central core. By studying the P and S waves generated by earthquakes we think we have a very good picture of the earth's deep interior. The main features are:
- mantle
- temperature from 300 K to 3000 K
- density about 5 g/cc
- pressure from 0 to 2 megabars
- liquid core
- temperature from 3000 K to 6500 K
- density about 12 g/cc
- pressure about 3 megabars
- convective motion coupled with rotation leads to the "dynamo" induced magnetic field of the earth
- solid core
- temperature 7000 K
- density about 12 g/cc
- pressure about 4 megabars