Abstract: In this paper, we studied the foreshocks of the global great shallow-focus earthquakes with MW≥8.0 from 1976 to 2017. Results show: ①27.6% of great earthquakes are preceded by foreshocks with maximum magnitude M＞5.0, which are all thrusting events and account for 38.1% of the total ones (the slip angle is in the range of 60?~110?). ②The epicenters of foreshock sequences are densely concentrated in space, and near the main shock. The epicenter distance between the largest foreshock and the main shock is 10~53km, the magnitude difference ΔM range from 1.1 to 2.8, and most of occurrence difference Δt (the occurring time interval of the largest foreshock and the main shock) is from two hours to 15 days. ③Compared with the background seismicity, the foreshock sequences has the characteristics of high frequency activity, and the accelerating process mainly appeared within 20 days before the main shock. ④The focal mechanism solutions of foreshocks are consistent with that of main shock, while that of aftershocks are more complex. ⑤Parameters of foreshocks and aftershocks for four great earthquakes were calculated by ETAS (Epidemic Type Aftershock Sequence) model. Results show that there is no regular difference between foreshocks and aftershocks for the α-value, meaning the ability to generate higher order aftershocks, and for the p-value, indicating the feature of sequence attenuation. While the b-value of foreshocks significantly lower than that of aftershocks. Compared with the regional b-value for background seismicity, the b-value of foreshocks is obviously lower, while that of aftershocks is higher or equivalent to.

摘要： 摘 要 本文系统研究了1976年至2017年全球29次MW≥8.0浅源地震的前震特征，发现：①27.6%（8次）的大震有前震，且最大前震震级M＞5.0。这8次大震均为逆冲型错动，断层滑动角为69?~110?，占逆冲型大震总数的36.4%；②前震序列空间分布集中，且集中在主震震中周围。最大前震与主震震中距为10~53km，震级差为1.1~2.8级，发震时间差主要为2小时至15天；③与背景地震活动相比，前震具有高频次活动的特点，加速活动主要发生在主震前20天内；④前震震源机制解与主震震源机制解一致，而余震震源机制解比较复杂；⑤使用ETAS模型计算了4个大震的前震和余震序列参数，结果显示，对于反映激发次级余震能力的α值和序列衰减快慢的P值，前震和余震没有规律性差异；而反映应力水平的b值则共性特征明显，前震b值明显低于余震；与区域背景b值相比，前震b值显著偏低，而余震b值高于或与区域背景b值相当。