1999年四川绵竹5.0级地震序列揭示的孕震结构  

Earthquake-generating Structure Revealed by 1999 Mianzhu Earthquake Sequence with M_S=5.0 in Sichuan

作　　者：赵珠[1] 汪碧澜[1] 龙思胜[1] 

机构地区：[1]四川省地震局,中国成都610041

出　　处：《中国地震》2001年第4期386-391,共6页Earthquake Research in China

摘　　要：通过对 1999年 11月 30日发生在龙门山断裂带中段的绵竹MS5 0地震序列震源位置的精确确定、主要地震震源机制解测定及序列的时间进程特征分析后 ,本文给出了该地震序列的震源断层分布、深度剖面、应力释放状况以及活动特征 ,进而揭示了该序列发生的孕震结构。结果表明 ,该序列的活动表现出下列特征 :①无明显的前震 ,所积累的应变能以突然的、近乎脉冲的方式释放 ,序列进程中无明显的起伏 ,大小地震的统计关系不太符合经典的G R估计。②序列震中均未分布在地表出露的龙门山山前主断裂上 ,而是出现在山前隐伏断裂附近 ,震中分布的取向与断裂走向不大一致 ;微观震中与宏观震中相距较远 ;震源深度分布在 5～ 16km范围。③震源断层面取向NE ,在NNE向的主压应力作用下 ,震源断层面表现出兼有逆断分量的走滑型错动。由此 ,我们认为大规模断裂带附近的地下隐伏断裂存在着更为值得重视的孕育地震活动的危险性。Through the accurate determination of hypocenter location,the measurement of the main focal mechanism solutions and the analyses of time dependent processes for Sichuan Mianzhu earthquake sequence with M S=5.0 occurred in the middle of Longmenshan fault zone on November 30,1999,the distribution of focal faults,the focal depth section,the stress release and seismicity features are given to reveal the earthquake|generating structure of the earthquake sequence.The obtained results show the activity features for thes sequence as follows:①There is non obvious foreshock,the accumulated strain energy releases in nearly pulse way,the seismic activity level is not quite evident fluctuating regulation during the duration of the sequence,and the statistical relation between the large events and the small events is less compatible with the traditional G|R estimation.②The epicenters of the earthquake sequence are not distributed on the main Longmenshan faults emerging out ground,but near the hidden Longmenshan piedmont faults.The direction of epicentral distribution is not very coincident with the fault strikes.The microscopic epicenter is relatively far from its macroscopic epicenter.The focal depths range from 5 to 16km.③The fractures of focal fault plane with the NE strike appear out the strike|slip displacement with some overthrust faulting under the major principal compressive stress of NNE direction.From these,we consider it should be paid more attentions to the underground hidden faults near some large scale fault zone for their generating earthquake risk.

关 键 词：绵竹地震序列 活动特征 震源位置 震源断层 隐伏断裂 1999年 孕震结构 

分 类 号：P315.2[天文地球—地震学]