Abstract: A systematic analysis of earthquake sequences of magnitudes MS ≥ 5. 0 in East China since 1970 shows that four types of earthquake sequences might be distinguished, i.e., the single type, the apparent single type-this is essentially a mainshock-aftershock type, which is to acestain extent similar to the single type, the mainshock-aftershock type and the swarm type, according to the magnitude difference between the largest and second largest earthquakes. Rather satisfactory results have been obtained in the investigation on the early determination of sequence type using that aftershock samples recorded during the periods of 0.5, 1, 2, 3, 5 and 7 days respectively after the mainshock. An attempt has been made to analyze the duration of aftershocks using a new method. Assuming a back-g round seismicity for a given area, the aftershock activity is considered to come to the end (on the whole), when the aftershock activity attenuates to this background value. The features of duration of aftershock sequences in the East China are discussed and the strength and frequencies of strong aftershocks are analysed using this method. Features of variations of the characteristic parametersb and for different type aftershock sequences are analysed. The features of the aftershock activity in this region discussed above can provide a scientific basis for accurate determination of seismicity trend that follows a major earthquake in the East China.

Key words: East China, Earthquake sequence, Earthquake type