Abstract: On January 15, 2000, an earthquake sequence including the main shock with M_S6.5 occurred in the Yao'an region of Yunnan Province. On July 21 and October 16, 2003, an earthquake sequence including the main shock with M_S6.2 and M_S6.1 occurred in the Dayao region of Yunnan Province. The epicenters of Yao'an earthquake and Dayao earthquake are both situated in Dian Zhong block and 42.5 km apart. The tectonics and the stress background of the earthquakes are similar, but the types of two sequences are different and the time interval is short. Based on horizontal-component digital seismograms recorded by Kunming Regional Digital Network, we obtain source parameters of the Yao'an earthquake sequence in 2000 and the Dayao earthquake sequence in 2003 using genetic algorithms. The results show that there is a good linear relation between seismic moment and local magnitude, the seismic moment is between 10¹² and 10¹⁴ N·m; the relation between seismic moment and the rupture radius remains a linear correlation. The stress drop seems independent of the local magnitude. The corner frequency increases with the seismic moment decreasing. Based on the expression between corner frequency and seismic moment by using least squares fitting, we can obtain the estimated value of corner frequency. Two earthquake sequences show different characteristics. The temporal variation in stress drops and in the difference between the calculated corner frequency and estimated corner frequency of the Yao'an earthquake sequence is the change from high to low before the strong aftershocks with M_S4.3~4.6, which indicates that there is a process of increasing and decreasing in the stress field of the aftershocks. Whereas the change of stress drops and difference between the calculated corner frequency and estimated corner frequency of the Dayao earthquake sequence has feature of high value before the aftershocks with M_S≥4.7, but the continuing time of high value anomalies before the aftershocks with M_S4.6 and M_S4.7 is shorter than that before the M_S6.1 earthquakes. The seismogenic fault and the type of these sequences were analyzed and discussed.

Key words: Source parameters, Yao'an earthquake sequence, Dayao earthquake sequence, Genetic algorithm