Do earthquakes occur only along faultlines?
As far as seismologists understand, all but the very deepest earthquakes (deeper than 600km) occur on faults. Seismic waves are generated when the two sides of the fault rapidly slip past each other. For most earthquakes, the faults do not break the surface, so the faults can be “seen” only through analysing the seismic waves. Faults can be anywhere from metres to a thousand kilometres long. Seismologists still have much to learn about the mechanism that causes the deepest earthquakes. At 600km, the earth is probably too warm for faults to be brittle like glass, so some sort of chemical change might occur very rapidly.
