During the period before and after the earthquake of magnitude 6.0 occurred on July 9, 1979 in Liyang, Jiangsu province, the observational station of electromagnetic waves in Nanjing(epicenter distance about 80 km)indicated the following three types of waves:
1. The electromagnetic, waves arising at the early stage before the earthquake are called waves type A;
2. The electromagnetic waves arising in the form of wave train before the approaching of the earthquake are called waves type B;
3. The electromagnetic waves arising after the earthquake characterizing both A and B are called waves type AB.
All sorts of the phenomena indicated that the characteristics of the electromagnetic waves arising during the approaching of the earthquake are:the nearer the occurrence of the earthquake approached, the higher the frequency of the electromagnetic waves. Moreover, the frequency spectrum of the electromagnetic wave sappeared to be wider than it is known today. In the continued duration in which the electromagnetic waves were arising, the group number of the wave train reached the peak value.