全球MW≥8.0浅源地震的前震序列研究  

STUDY ON FORESHOCK SEQUENCES OF THE GLOBA L GREAT SHALLOW-FOCUS EARTHQUAKES WITH MW≥8.0

作　　者：薛艳[1] 解孟雨 刘杰[1] 庄建仓 XUE Yan;XIE Meng-yu;LIU Jie;ZHUANG Jian-cang(China Earthquake Networks Center,Beijing 100045,China;The Institute of Statistical Mathematics,Tokyo 106-8569,Japan)

机构地区：[1]中国地震台网中心,北京100045 [2]日本东京数理统计研究所,东京190—8562

出　　处：《地震地质》2021年第5期1233-1249,共17页Seismology and Geology

基　　金：国家重点研发计划项目(2017YFC1500304);国家自然基金(41774069)共同资助。

摘　　要：前震是短临地震预报最有效的方法之一。文中系统研究了1976—2017年全球29次MW≥8.0浅源地震的前震特征,发现:1)共有8次大地震出现前震,占总数的27.6%,且最大前震的震级M>5.0。这8次大地震均为逆冲型,占逆冲型地震总数(23次)的34.8%;2)前震序列的空间分布集中,且集中在主震震中周围。最大前震与主震的震中距为10~53km,震级差为1.1~2.8级。87.5%的时间差(最大前震与主震的发生时间差)为2h~15d,仅2006年11月15日千岛群岛8.3级地震前45d发生6.6级最大前震;3)与背景地震活动相比,前震具有高频次活动的特点。在8次大地震中,5次在主震前15d内加速活动;3次加速活动的开始时间超过1个月(35~45d),但在主震前1d和6d又再次出现前震频次显著增多的现象;4)前震的震源机制解与主震一致,而余震的震源机制解比较复杂;5)使用ETAS模型计算前震和余震序列的参数α、p和b值。为了确保参数计算的可靠性,文中约定当前震序列满足计算样本量N≥30且最低计算震级Mj≥Mc(Mc为最小完备震级)时,才同时计算前震和余震序列参数。此外,文中约定余震序列的持续时间为主震后1个月。在8次大地震中,有4个可以进行对比计算。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值低于区域背景b值的10%~24%。前震b值与区域背景b值之差是区域背景b值标准差的2.2~7.1倍,具有显著性。而余震b值高于区域背景b值或与其相当。为了讨论前震b值的稳定性,计算了2个资料丰富的前震序列的b值随样本量的变化。结果显示,在前震序列的开始阶段b值较低,之后逐渐增大,当计算样本量N≥70后,b值基本稳定。Of all of the short-term and imminent precursors,foreshocks are recognized as one of the most effective indicators for earthquake prediction.This paper studies the statistical characteristics of foreshock activity of 29 global great shallow-focus earthquakes with MW≥8.0 from 1976 to 2017.Among these earthquakes,there are 23 thrusting ones.Results show that there are 8 great earthquakes with foreshocks,accounting for 27.6%of the total.In addition,the 8 great earthquakes with foreshocks are all thrusting events,accounting for 34.8%of the total thrusting earthquakes.The maximum magnitude of foreshock is greater than 5.0.The 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 differenceΔM between the maximum foreshock and the main shock ranges from 1.1 to 2.8,and the origin time differenceΔt(the interval between the origin time of the largest foreshock and that of the main shock)is from 2 hours to 15 days for 87.5%of the earthquakes except the Kuril Islands MW8.3 earthquake,which occurred on November 15,2006,while its maximum foreshock of MW6.6 occurred 45 days before the MW8.3 main shock.Compared with the background seismicity,the foreshock sequence has the characteristic of high frequency.Of the eight earthquakes,the seismicity of five foreshock sequences accelerated within 15 days before the main shock,for the other three the seismicity began to increase during 35~45 days prior to the main shock,and the frequency increased again one day and six days before the main shock.The focal mechanisms of foreshocks are similar to that of the main shock.While the focal mechanism of aftershock sequences is complicated and diverse.Such consistency of focal mechanisms with main shocks did not exist in aftershock sequences.The parameters,α-value,p-value and b-value of foreshocks and aftershocks were calculated by the ETAS(Epidemic Type Aftershock Sequence)model,and b-value was got by the m

关 键 词：前震序列 余震序列ETAS模型 B值 

分 类 号：P315.2[天文地球—地震学]