关键词: 汶川8.0级地震, 分段特征, 序列类型, 最大强余震震级, 强余震活动持续时间, 破裂尺度

Abstract: Aftershock activity ofMay 12 M8.0 W enchuan Earthquake sequence shows an obvious segmen-ted feature,most of the large aftershocks are d istributed in the south and north parts of aftershock zone.Thrusting is dom inant in the south partwith a small strike slip component.The aftershock activ-ity decays gradually and presents the sequence feature ofmainshock-aftershock pattern.The north part is the end ing area of the mainshock fracture,where the strike slipping is dom inant and shows an obvi-ous swarm feature,it therefore became the major area for large aftershocks.Modulation of earth tide on aftershock activity is remarkable,most of large aftershocks occur during the period of flood and neap tide.The time period around 16:00 is the dom inant occurring time for large aftershocks.Thep-val-ue,a parameter ofmod ified Omori formula,increases gradually with time,and reaches about 1 in the final.Based on the previous study,the sequence patterns,magnitude ofmaximum aftershock,as well as the duration of aftershock activity have been d iscussed.The primary results also show that the mag-nitude d ifference between mainshock and the maximum aftershock is proportional to the rupture size of the mainshock for huge earthquakes of about M8.0.This means that,when the magnitudes of earth-quakes are nearly the same,large rupture size corresponds to the sufficient energy release.

Key words: the May 12^th M8.0 Wenchuan earthquake, segmentation features, sequence pattern, magnitude ofmaximum aftershock, duration of aftershock activity, rupture size