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全球浅源巨大地震序列统计特征
薛艳1, 刘杰1, 刘双庆2
1.中国地震台网中心, 北京市西城区三里河南横街5号 100045;2.天津市地震局, 天津 300201
摘要:
系统研究了1976年以来全球58次MW ≥ 7.8浅源地震序列的统计特征。结果显示:①在58次巨大地震中,板间地震45次,板内地震13次,板内地震强度低于板间地震。②74.1%的板间地震为逆断层错动,61.5%的板内地震为走滑型错动。③58次地震序列中,82.8%为主-余型,17.2%为多震型;与5级以上地震序列不同,巨大地震没有孤立型,其余震比较活跃;板内地震中,多震型占7.7%,而板间地震中多震型占20%。④对于主-余型序列,75%的主震与最大余震的震级差为1.0~2.0级;震级差与主震震源错动类型有关,走滑型的震级差明显大于逆冲型;68%的最大余震发生在主震后3天内,其次为10天左右与1个月左右;49%的Dmax-aft(最大余震震中与主震震中间的距离)不超过余震区长轴的1/3,31%的Dmax-aft为余震区尺度的1/3~1/2;最大余震的发生时间、最大余震震中与主震震中间的距离同主震断层错动类型间的关系不明显。⑤应用ETAS模型计算了46个序列参数后发现,b值、p值和a值均呈Beta分布,b值平均为1.164±0.211,p值平均为1.559±0.412,a值平均为1.673±0.911;p值和a值分布分散;对于不同的序列类型、震源错动类型及板内、板间地震,b值差异不显著;逆冲型序列p值明显大于走滑型和正断层型;板间地震序列a值明显小于板内地震;逆冲型序列a值明显小于走滑型和正断层型;这表明,与板内地震相比,板间地震具有较强的"余震激发余震"的能力;逆冲型破裂虽然会导致序列衰减较快,但触发次级余震的能力相对较强。⑥逆冲型巨大地震余震区长轴L的对数与主震震级MW间的拟合关系式为lgL =(-1.399±0.306)+(0.470±0.037)MW
关键词:  浅源巨大地震  序列类型  主-余型  多震型  孤立型  板内地震  板间地震
DOI:
分类号:P315
基金项目:中国地震局地震科技星火计划项目(XH17048、XH17003Y)共同资助
Statistical Characteristics of the Global Great Shallow-focus Earthquake Sequences
Xue Yan1, Liu Jie1, Liu Shuangqing2
1.Earthquake Networks Center, Beijing 100045, China;2.Tianjin Earthquake Agency, Tianjin 300201, China
Abstract:
In this paper,we studied the statistical characteristics of 58 global great shallow-focus earthquake sequences with MW ≥ 7.8 since 1976. Results showed:① There are 45 interplate events and 13 intraplate shocks among the 58 great earthquakes. The magnitude of intraplate earthquakes is lower than that of interplate ones. ② 74.1% of the interplate earthquakes are thrusting ones,and 61.5% of intraplate earthquakes are strike slips. ③ Among the 58 large earthquake sequences,82.8% are of the mainshock-aftershock type and 17.2% are of the multiple mainshock type. Different from the M ≥ 5.0 earthquake sequences,there is no isolated earthquake type in great earthquake sequences and their aftershock activity levels are high. The proportion of multiple mainshock type in intraplate earthquakes and interplater earthquakes is 7.7% and 20%respectively. ④ For the mainshock-aftershock sequences,events with magnitude difference △M between the main shock and the largest aftershock ranging from 1.0 to 2.0,consist of 75% of the total. The △M value of the strike-slip sequence is obviously larger than that of the thrust type. 68% of the largest aftershocks occurred during 3 days after the main shock,and secondly occurred about 10 days and about 1 month. The 49%epicentral distances Dmax-aft of the mainshock and the largest aftershock are not exceed one-third of the aftershock zone scale,and 31% is from one-third to one-half of the aftershock zone scale. The differences of △t (the occurring time interval of the mainshock and the largest aftershock)and Dmax-aft are not obvious for different modes of mainshock fracture. ⑤ Parameters of 46 earthquake sequences were calculated by ETAS(Epidemic Type Aftershock Sequence)model. The data of b-value,p-value and a-value are of beta distribution. The average b-value is 1.164±0.211,the average p-value is 1.559±0.412 and the average a-value is 1.673±0.911. It is seen that p-value and a-value are dispersed. The differences of b-value are not obvious for different types of earthquake sequences,for different modes of mainshock fracture,for intraplate and interpolate earthquakes. The p-value of the sequence with the main shock as a thrust is greater than that of the strike-slip and normal faults. The a-value of the interplate earthquake sequences is smaller than that of the intraplate ones. This indicates that the interplate earthquake has a high ability to generate higher order aftershocks. The a-value of the sequence with thrusting fracture mainshock is smaller than that of the strike-slip and normal fracture. This means although thrust rupture can cause faster decay of sequences,the ability to generate higher order aftershocks is relatively strong. ⑥ The fitting relation between the scale of aftershock area L and the magnitude of mainshock MW for thrust earthquakes is lgL=(-1.399±0.306)+(0.470±0.037)MW.
Key words:  Shallow-focus large earthquake  Sequence type  Mainshock-aftershock sequence type  Multiple mainshock type  Isolated earthquake type  Intraplate earthquake  Interplate earthquake