Abstract: 294 earthquake sequences with magnitude greater than or equal to 5.0 occurred in China's mainland from 1970 to 2003 have been collected. Among of them, 68 are isolated earthquakes, 174 are mainshock-aftershock sequences and 52 belong to the multiple mainshock type. 9 parameters, such as h value, b value, energy entropy and so on, of these sequences have been calculated in different periods after the mainshock. With the given confidence level, a=0.05, average value of each parameter and its confidence limitation have been calculated for each sequence types, which are taken as the criterion index for classification of aftershock sequences. Based on the data, the changing characteristics of parameters and their capability for classification of aftershock sequences have been discussed. Generally, most selected parameters express the capability for classification of aftershock sequences to a certain extent. Among them, the numerical range of some parameters (such as energy entropy, time entropy, difference of the magnitude and so on) is concerned with the magnitude of mainshock and the classification rule is different when the mainshock are distributed in different magnitude range. Some parameters (such as normalized frequency, h value and so on) change with the time and there is different classification rule in different period after the mainshock. The time range, in which the parameter is available for classification of aftershock sequences, is different for different parameters, and some parameters seldom have the ability to classify the aftershock sequences, such as b value, normalized energy, average magnitude, and so on. For parameters which have a certain capability for classification of aftershock sequences, the suitable condition for daily use and the real judgment index which concerning with the lapse time from the mainshock and magnitude of mainshock have been given. Roughly and averagely, several parameters, such as energy entropy, magnitude difference between mainshock and the largest aftershock and so on, have a high identification rate for classification of aftershock sequences.

Key words: Classification of aftershock sequences, Isolated earthquake type, Mainshock-aftershock type, Multiple mainshock type, Sequence parameters