汶川8.0级地震序列的时—空扩展与强余震趋势的阶段性估计
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摘要
根据2008年5月12日汶川8.0级地震丰富的余震序列资料,研究了余震活动的时—空扩展过程及分段破裂特征。汶川8.0级地震余震序列呈现有起伏的衰减,前期高频次,衰减快,后期衰减慢,持续时间长。在时间序列出现较强起伏的地震均集中发生在余震带北段,而南段余震活动持续处于平稳状态。密集余震沿NE向龙门山构造带的中央断裂呈窄条形展布330km,深度分布几到40余km。垂向余震带走向(NE方向)的地震深度剖面(NW向截面)和余震密集区图像呈现不对称的锲形分布。这与龙门山推覆构造带的受力作用方式有关。余震区较强余震明显分为南段和北段。研究了较强余震的震源机制及分段特征。给出强余震趋势的基本分析方法,地震类型判定,强余震趋势的阶段性估计效果,以及目前现场地震预报应注意的问题。
Based on rich observation data of the 2008 M8.0 Wenchuan Earthquake,we study rupture characters of the faults and the temporal-spatial development of aftershock sequences.The intensity change of aftershock sequences of the 2008 M8.0 Wenchuan Earthquake shows a fluctuate attenuation.In the first half period the attenuation rate of seismic frequency is high and in the later half it is low.The continuation time of seismic attenuation is long.The most of area of seismicity with strong fluctuation is the north segment of seismic fault and the weak seismicity area is the south segment.The aftershock area with heavy intensity distribute along the central segment of Longmengshan faults,which is the seismic belt with 330 kilometers long.The hypocenter depth ranges from several kilometers to 40 kilometers.The vertical profile images formed by the seismic belts of strong aftershocks with the northeast direction show an unsymmetrical wedge distribution.It is relate to the force effecting ways of the nappe structure of Longmenshan faults.The aftershock distribution shows two segments,north and south segments.At the same time,the focal mechanism solutions and the segmental characteristics of strong aftershocks are analyzed.In this paper,we introduce how to judge earthquake tendency,earthquake types,earthquake phases and the tips in the earthquake fieldwork of the 2008 M8.0 Wenchuan Earthquake.
Based on rich observation data of the 2008 M8.0 Wenchuan Earthquake,we study rupture characters of the faults and the temporal-spatial development of aftershock sequences.The intensity change of aftershock sequences of the 2008 M8.0 Wenchuan Earthquake shows a fluctuate attenuation.In the first half period the attenuation rate of seismic frequency is high and in the later half it is low.The continuation time of seismic attenuation is long.The most of area of seismicity with strong fluctuation is the north segment of seismic fault and the weak seismicity area is the south segment.The aftershock area with heavy intensity distribute along the central segment of Longmengshan faults,which is the seismic belt with 330 kilometers long.The hypocenter depth ranges from several kilometers to 40 kilometers.The vertical profile images formed by the seismic belts of strong aftershocks with the northeast direction show an unsymmetrical wedge distribution.It is relate to the force effecting ways of the nappe structure of Longmenshan faults.The aftershock distribution shows two segments,north and south segments.At the same time,the focal mechanism solutions and the segmental characteristics of strong aftershocks are analyzed.In this paper,we introduce how to judge earthquake tendency,earthquake types,earthquake phases and the tips in the earthquake fieldwork of the 2008 M8.0 Wenchuan Earthquake.
引文
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[11]钟继茂,程万正.由多个地震震源机制解求川滇地区平均应力场方向[J].地震学报,2006,28(4):337-346.
[12]陈学忠,李艳娥,郭祥云.2008年5月12日四川汶川8.0级地震前后震源区应力水平估计[J].国际地震动态.2008,354(6):1-3.
[2]吴开统,焦远碧,吕培苓等.地震序列概论[M].北京:北京大学出版社.1990.
[3]张四昌,王绍晋,刁桂苓等.1974年永善—大关地震序列的破裂特征[J].地球物理学报.1994,37(Supp):170-176.
[4]程万正.巴塘6.7级震群非单一指数衰减的复杂时序结构[J].地震学报.1992,14(Supp):600-611.
[5]刁桂苓,于利明,宁杰远等.1989年大同震群的破裂特征[J].地球物理学报,1993,36(3):360-368.
[6]程万正,陈天长.1989年巴塘6.7级震群的复杂时—空扩展和震源力学机制[J].地震学报,1994,16(2):153-159.
[7]王洋龙,覃玉玺,顾正光等.1988年澜沧—耿马双主震型地震破裂与震区的现代构造运动[J].地震研究.1994,17(1):46-54.
[8]程万正,罗灼礼.从巴塘、小金、江北地震论地震类型的判定[J].地震,1990,(6):53-64.
[9]朱介寿.汶川地震的岩石圈深部结构与动力学背景[J].成都理工大学学报(自然科学版),2008,35(4)348-356.
[10]陈运泰,许力生,张勇等.2008年5月12日汶川特大地震震源特性分析报告[R].http://www.csi.ac.cn/sichuan/chenyuntai.pdf(in Chinese).
[11]钟继茂,程万正.由多个地震震源机制解求川滇地区平均应力场方向[J].地震学报,2006,28(4):337-346.
[12]陈学忠,李艳娥,郭祥云.2008年5月12日四川汶川8.0级地震前后震源区应力水平估计[J].国际地震动态.2008,354(6):1-3.
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