汶川地震区断层围陷波探测

对汶川地震区开展震后科考和断层围陷波探测,本文主要介绍平通镇断层围陷波探测及初步结果。平通镇处在汶川8．0级地震断层带正上方,地表破坏十分严重。该断层围陷波测线横跨断层,以地震探槽为大致中点,沿NW—SE方向两端延伸,测线长约400m。这次观测结果表明,在汶川8．0级地震的新破裂带中可以观测到断层围陷波,反映了断层带内外的介质在物理性质上有较大的差异。该测线记录的断层围陷波优势频率大约为3—4Hz。探槽附近的台站断层围陷波较强,初步推测,该地段地壳内断层的宽度大约有200m。     

断层围陷波观测和应用

断层围陷波的观测特点是利用密集的地震台阵,横跨断层布设测线。可以利用爆炸震源也可以利用余震进行观测,本文分别介绍了实际观测的例子。对大地震破裂带内部的观测,测线位置通常布设在地表破裂带明显、已开挖了地震探槽、断层陡坎出露等地震地质的典型地段。利用爆炸震源激发观测断层围陷波,震源位置应尽量选择在断层带上,震源炸药量大约500kg,测线位置与震源的距离大约5—15km。断层围陷波在新破裂带和老的断层中都能形成和传播,因此该方法可以用于大震破裂带研究,也可以用于城市活断层探测。     

昆仑山断层围陷波的分析和研究

对2001年昆仑山口西Ms81级地震产生的断层带,布设了沿断层和横跨断层的两条人工地震测线.通过对观测资料的定量分析和处理,求得了昆仑山断层带内部的细结构.分析工作包括从S波震相开始的振幅谱计算、速度频散计算、群速度测量,并用面波频散方法反演S波速度结构,用振幅谱比的方法估计断层带的Q值.野外试验结果表明,S波震相与围陷波组的时间差随炮点与台站之间距离增大而增加,在断层带外的测点上观测到与断层带相关的场地效应.最后得出昆仑山断层带宽度为250m、速度结构为断层内低速的分层结构和Q值为15（断层内）和30（围岩）.虽然昆仑山口西地震的震级比美国加州Landers地震的震级（Ms76）大,且地震产生的破裂带长度长得多,但是这两个地震断层带的宽度却相差不大.     

汤西断裂的断层围陷波初步研究

作为断层围陷波方法在城市活断层探测中的首次尝试,我们针对太行山山前断裂带南段的汤西断裂开展了爆炸震源的观测试验。运用数字滤波和频谱分析等技术,由地震记录图分离出了断层围陷波。根据2横测线的观测结果,可确定断层的位置,并可推测断层在该处宽度为200～300m。破裂面较宽,可能与其张性特征有关。分频道地震图显示,断层围陷波具有正频散现象,其低频分量传播较快。这表明断层围陷波是一种面波,可利用其频散规律研究断裂带内介质的物理性质。这次的观测结果也表明,断层围陷波并不局限于新破裂带,在老断层中也能形成和传播。事实上,只要断层带内外的介质在物理性质上有较大的差异,均能产生沿断层传播的围陷波。在城市活断层探测中,断层围陷波的方法具有非常独特的优越性     

利用断层围陷波资料研究汶川M_S8.0地震构造特征

利用汶川地震区不同地段的断层围陷波记录,分析了该地震断层的分段性特征。对断层北东段的关庄测线分析研究结果表明：地壳内破碎带的宽度大约160~180m,地下破碎带的中间与地表破裂的位置对应,并且地下破碎带在断层的两盘边缘较均匀地分布,反映了北东段的断层倾角较陡,近似直立断层。对断层南西段的虹口测线研究结果表明：地壳内破碎带的宽度大约180~200m,地下破碎带主要分布在地表断层陡坎上盘所对应的地壳内,反映了南西段断层倾角比北东段断层倾角小。本文的研究结果可以为汶川8.0级地震的构造背景研究提供依据。     

昆仑山口西8.1级地震地表破裂参数相互关系的新认识

地震地表破裂带调查表明,昆仑山口西 8. 1级地震的破裂长度为 426km,最大水平位移6m左右,地震破裂位移的分布明显地受断层活动段控制。该次地震的破裂长度远大于统计值,文中应用地壳极限线应变的概念,通过比较中国大陆内部几次走滑型强震的地震破裂最大位移与破裂长度的关系,论述了昆仑山口西 8. 1级地震中各次级段破裂的相对独立特征,认为该次强震不是一次整体性破裂事件,而是由连续触发的几次地震组成     

基于动摩擦应力下调滑移弱化机制，利用地表破裂同震位移约束2001年昆仑山口西MS8.1地震破裂传播速度

利用2001年昆仑山口西MS8.1地震现场观测所提供的地表破裂同震位移数据,使用简单滑移弱化破裂模型,估算了发震主断层上的破裂传播速度. 该模型中考虑了断层破裂时动摩擦过程中应力上调和下调机制对地震波辐射能量分配的影响. 对比Bouchon和Valleacute;e有关昆仑山口西地震主断层破裂传播速度超过剪切波速度,甚至达到P波速度的结果, 采用动摩擦应力下调时的滑移弱化模型 (分数应力降模型),结果表明,伴随较高的地震波辐射效率,主断层的平均破裂传播速度等于或小于瑞利波速度,这与许力生和陈运泰的体波反演结果,以及陈学忠震源应力场估算的结果是一致的. 最后,联系到由地表破裂现象所反映出的断层力学特征,如与视应力相关的分数应力降 (动摩擦应力下调), 基于滑移弱化模型, 讨论了可能的震源破裂机制.      

昆仑山口西MS 81级地震地表破裂带高分辨率卫星影像特征研究

2001年11月14日昆仑山口西发生81级地震.应用高分辨率卫星影像进行地震地表破裂带解译，10m分辨率SPOT卫星影像能够清楚地反映出地震地表破裂主破裂带的形迹, 1m分辨率IKONOS影像能反映出地震地表破裂的精细结构及运动特征.结果表明，昆仑山口西81级地震地表破裂带主要位于东昆仑断裂南麓冲洪积台地或冲洪积台地后缘的地貌陡变带和断层谷地里，是一条叠置在先存破裂带上的地震破裂带.在布喀达坂峰以东的地表破裂带长近350km，由3条次级破裂组成，走向100°.流经破裂带的一系列沟谷发生左旋同步扭曲，平均滑动速率为134～168mm/a，属AA级活动水平.最大左旋位错78m，地震破裂带最宽达1250m，宏观震中位于93°17′E，35°47′N，即玉西峰附近的地震地表破裂带上.     

断层带围陷波研究及其应用进展

断层带结构研究对于认识地震的孕育发生、地震破裂过程及其地震灾害具有重要的意义,因而多种方法被用来观测和研究断层带结构,其中断层带围陷波就是有效方法之一.断层带围陷波是由地震波入射到断层带内低速介质与高速围岩之间的界面时在界面内侧经多次反射相干叠加形成,具有大振幅、低频率和频散的特点.由于断层带围陷波在断层带的内部传播,它携带有断层带的介质物性和结构的重要信息,因此可以利用围陷波的波形特征研究断层带的精细结构.本文详细介绍了断层带围陷波的形成机制、传播和特性,全面阐述了断层带围陷波在观测研究、传播和特性理论研究和利用围陷波反演断层带结构的方法及应用三个方面的进展,并探讨了断层带围陷波研究方面存在的不足和问题.     

昆仑山口断裂的通道波观测

青藏高原位于欧亚板块与印度板块碰撞的结合部位,地震活动十分强烈,近年来多次发生大地震。2001年11月14日青藏高原内部的昆仑山口断裂带西端发生8．1级强烈地震,这是我国大陆近50年来最强烈的一次地震。该地震造成的地表破裂长达300余千米,最大水平错距达5～6m,因此,昆仑山口断裂是观测断层通道波的极好场所。为了进行地震断裂通道波的观测及研究昆仑山口断裂带的几何参数和力学性质,中国地震局地球物理勘探中心于2002年3月下旬～4月中旬在震区布设了一条地震测线,记录到余震800多次。通过昆仑山口断裂带的断层通道波的观测获得了断层通道波的清晰震相,并掌握了断层通道波的运动学特征、频率特征,为城市盲断层的探测提供了可靠的科学方法。     

Study on rupture zone of the <Emphasis Type="Italic">M</Emphasis>=8.1 Kunlun Mountain earthquake using fault-zone trapped waves

The observation of the fault-zone trapped waves was conducted using a seismic line with dense receivers across surface rupture zone of the M=8.1 Kunlun Mountain earthquake. The fault zone trapped waves were separated from seismograms by numerical filtering and spectral analyzing. The results show that: a) Both explosion and earthquake sources can excite fault-zone trapped waves, as long as they locate in or near the fault zone; b) Most energy of the fault-zone trapped waves concentrates in the fault zone and the amplitudes strongly decay with the distance from observation point to the fault zone; c) Dominant frequencies of the fault-zone trapped waves are related to the width of the fault zone and the velocity of the media in it. The wider the fault zone or the lower the velocity is, the lower the dominant frequencies are; d) For fault zone trapped waves, there exist dispersions; e) Based on the fault zone trapped waves observed in Kunlun Mountain Pass region, the width of the rupture plane is deduced to be about 300 m and is greater than that on the surface.     

Study on rupture zone of the M=8.1 Kunlun Mountain earthquake using fault-zone trapped waves

Introduction The study on deep crustal faults has been one of the most vigorous subjects in seismology. In the past, 3-D deep seismic sounding and 3-D seismic tomography were usually used for this pur-pose. But it is difficult to obtain the fine structures of the faults in deep crust by these methods. Recently, seismologists in the world pay more attention to the fault zone trapped waves. Since the fault-zone trapped waves arise from coherent multiple reflections at two boundaries of the fau…     

Study on rupture zone of the M =8.1 Kunlun Mountain earthquake using fault-zone trapped waves

The observation of the fault-zone trapped waves was conducted using a seismic line with dense receivers across surface rupture zone of the M=8.1 Kunlun Mountain earthquake. The fault zone trapped waves were separated from seismograms by numerical filtering and spectral analyzing. The results show that: a) Both explosion and earthquake sources can excite fault-zone trapped waves, as long as they locate in or near the fault zone; b) Most energy of the fault-zone trapped waves concentrates in the fault zone and the amplitudes strongly decay with the distance from observation point to the fault zone; c) Dominant frequencies of the fault-zone trapped waves are related to the width of the fault zone and the velocity of the media in it. The wider the fault zone or the lower the velocity is, the lower the dominant frequencies are; d) For fault zone trapped waves, there exist dispersions; e) Based on the fault zone trapped waves observed in Kunlun Mountain Pass region, the width of the rupture plane is deduced to be about 300 m and is greater than that on the surface. Foundation item: Joint Earthquake Science Foundation of China (201001). Contribution No. RCEG200305, Research Center of Exploration Geophysics, China Earthquake Administration.     

昆仑山断裂带围陷波的有限差分数值模拟解释

利用交错网格有限差分方法对昆仑山断裂带人工爆破产生的围陷波进行了三维数值模拟解释.为提高断裂带最终模型的可信度，在围陷波模拟的同时考虑了人工爆破记录的三个分量.对昆仑山断裂带围陷波的模拟结果表明，影响围陷波特性的断裂带深度主要在10 km以内.S波速度和断裂带宽度对围陷波的到时、频率、振幅和相位影响较大.数值模拟解释获得的昆仑山断裂带的细结构参数是：浅部断裂带宽度为300 m，深部为250 m；深度在400 m以上断裂带内S波速度为098 km/s，外部围岩S波速度为170 km/s，Q值为138；S波速度和Q值随着深度的增加而增加；1000 m以下断裂带内S波速度为280 km/s，围岩S波速度为33 km/s.     

2001年昆仑山口西MS8.1地震破裂时空过程的统一模型

2001年昆仑山口西M_S8.1地震经历了一个复杂的破裂过程,其破裂长、幅度大、破裂速度多变,成为大陆型地震研究的典型地震。本文融合近场高精度大地测量观测（4幅InSAR影像,34个GPS点位同震位移）和高信噪比远震波形记录,基于有限断层反演理论,联合反演得到该地震同震破裂时空过程的统一模型;同时,基于欧洲区域台网波形数据,利用反投影方法获得高频破裂的时空展布。联合反演结果表明,破裂自西向东传播的过程中走向有所变化,破裂尺度达400km,最大滑移量达8m,地震矩大小为6.1×10²⁰Nm,对应的矩震级M_W为7.78。主断层破裂经历了3个阶段,其中,超剪切破裂阶段对应最大位错区域,破裂到达西大滩段与昆仑山口断层交叉处时,破裂速度与尺度迅速下降。反投影结果同样显示破裂的3个阶段空间上对应大地测量反演的3个最大破裂区,最大破裂区的扩展速度达6km/s,但超剪切破裂终止在断层交叉口东部约30km处断层走向发生转变的位置。     

Rupture behavior and deformation localization of the Kunlunshan earthquake (<Emphasis Type="Italic">M</Emphasis><Subscript><Emphasis Type="Italic">w</Emphasis></Subscript>7.8) and their tectonic implications

Earthquake surface rupture is the result of transformation from crustal elastic strain accumulation to permanent tectonic deformation. The surface rupture zone produced by the 2001 Kunlunshan earthquake (M _w 7.8) on the Kusaihu segment of the Kunlun fault extends over 426 km. It consists of three relatively independent surface rupture sections: the western strike-slip section, the middle transtensional section and the eastern strike-slip section. Hence this implies that the Kunlunshan earthquake is composed of three earthquake rupturing events, i.e. the M _w =6.8, M _w =6.2 and M _w ⩽=7.8 events, respectively. The M _w =7.8 earthquake, along the eastern section, is the main shock of the Kunlunshan earthquake, further decomposed into four rupturing subevents. Field measurements indicate that the width of a single surface break on different sections ranges from several meters to 15 m, with a maximum value of less than 30 m. The width of the surface rupture zone that consists of en echelon breaks depends on its geometric structures, especially the stepover width of the secondary surface rupture zones in en echelon, displaying a basic feature of deformation localization. Consistency between the Quaternary geologic slip rate, the GPS-monitored strain rate and the localization of the surface ruptures of the 2001 Kunlunshan earthquake may indicate that the tectonic deformation between the Bayan Har block and Qilian-Qaidam block in the northern Tibetan Plateau is characterized by strike-slip faulting along the limited width of the Kunlun fault, while the blocks themselves on both sides of the Kunlun fault are characterized by block motion. The localization of earthquake surface rupture zone is of great significance to determine the width of the fault-surface-rupture hazard zone, along which direct destruction will be caused by co-seismic surface rupturing along a strike-slip fault, that should be considered before the major engineering project, residental buildings and life line construction. Supported by the National Natural Science Foundation of China (Grant No. 40474037) and the National Basic Research Program of China (Grant No. 2004CB418401)     

利用基于围陷波波形相关的网格搜索法确定昆仑山断裂带结构参数

提出了确定断层带结构的一种方法,它利用基于断层带围陷波波形相关的网格搜索法,以定量地确定断层带参数.该方法通过建立一系列由断层带的相关参数构建的断层带结构模型,利用有限差分方法数值模拟每组参数对应的断层带模型所产生的围陷波,并与实际观测围陷波波形进行相关分析,计算由以断层参数为多维网格坐标的相关系数变化趋势,网格搜索其峰值,最终获得最佳的一组参数,并确定断层带的结构.本文对昆仑山断裂带人工激发的围陷波进行分析,利用该方法确定了断裂带宽度和Q值参数.