Some seismic contributions to knowledge of the Earth's crust

Some very positive facts about the Earth have come from seismology. These include: The existence of a quite sharply defined core; the possibility of quite accurate location of normal‐depth earthquakes, because the transmission‐time of the same kind of waves through the Earth is approximately the same for the same distance in all parts of the Earth; the occurrence of deep‐focus earthquakes and determination of their depth; and finally the occurrence of high‐speed surface‐waves over the Pacific Basin.