Geoscience Reference
In-Depth Information
depth, which in practice means in low-velocity regions. Within the Earth, therefore, the
method fails for those parts of the upper mantle where there are low-velocity zones and at the
core-mantle boundary. Other difficulties occur because of the lack of exact spherical
symmetry within the Earth and the fact that the time-distance curves are not completely
error-free (this means that the S-wave structure is less well determined than the P-wave
structure since S-wave arrival times are more difficult to pick).
