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.     

P波入射下断层参数对地表地震动的影响

基于应用透射人工边界条件的显式有限元法计算断层破碎带宽度及力学参数变化、地震动入射角变化时二维断层场地模型P波入射下地表地震动场的分布。结果表明:(1)低速度破碎带的存在导致整个场地都有P波转换为SV波的分量,且在断层破碎带的区域出现断层陷波;(2)低速度破碎带的存在使输入场地恒定的能量向破碎带集聚放大,随着破碎带宽度增大或其介质波速降低集聚放大效应增大;(3)场地放大效应是频率相关的,宽度较宽或介质波速较低的断层破碎带对输入地震动中较低的频率成份放大显著;(4)竖向断层破碎带能阻隔斜入射地震P波,随着入射角增加隔震效应更显著。     

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     

二维非均匀介质地震波传播的伪谱和有限差分混合方法的应用研究

<正>由于围陷波产生于低速带内物质与高速围岩的界面上,在带内传播时间较长,因此它的振幅和频率特征对断层带形态和带内物质性质敏感,对断层带围陷波的观测与分析能够提供断层带精细结构的重要信息。基于伪谱法和有限差分混合数值模拟方法,开展了沉积层对隐伏断裂带围陷波影响的研究,探讨了沉     

利用断层围陷波研究昆仑山口西8.1级地震破裂面

利用横跨地表破裂带的小点距的地震测线, 对2001年11月14日昆仑山口西8.1级地震进行了断层围陷波的观测实验. 经过数字滤波和频谱分析等技术, 由地震记录图中分离出了断层围陷波. 资料处理结果表明: ① 无论是人工地震震源还是天然地震震源, 只要位于断层带内或紧靠断层带, 均能激发断层围陷波; ② 断层围陷波的能量主要集中于断层带内, 其振幅随测点与断层带距离的增加而急剧衰减; ③ 断层围陷波的优势频率与断层的宽度及断层带内介质的速度有关, 断层带越宽, 或断层带内部介质速度越低, 则观测到的断层围陷波的优势频率越低; ④ 断层围陷波存在着频散现象; ⑤ 根据昆仑山口西地震测线断层围陷波的观测结果, 可推断该处破裂面宽度为300 m左右, 远远大于地表破裂带的宽度.      

利用断层围陷波资料研究龙门山断裂带分段特征

正断层围陷波(Fault zone trapped waves)又称为断层通道波、断层导波、槽波,是波在断层的两个边界内侧多次反射并相干迭加而形成的。围陷波既然是由断层带内低速介质和高速围岩之间的相干多次反射波构成的,那么其振幅和频率就强烈地依赖于断层带内介质的物理性质和断层的几何形态。所以观测、分析和模拟断层围陷波能够确定断层的深部细节。2008年5月12日在四川汶川发生了8级大地震,随后强余震不断,并且2013年4月20日     

松软覆盖层对隐伏断层带围陷波的影响研究

利用二维非均匀介质地震波传播的伪谱和有限差分混合方法,通过数值计算,讨论了松软覆盖层对隐伏断层带围陷波特征的影响.在没有覆盖层的情况下,围陷波振幅和围岩上相比明显增加,持续时间变长.覆盖层造成围岩上地面运动振幅增大,围陷波的部分能量传播到覆盖层中,使得围陷波的能量变小.随着覆盖层厚度增加,围陷波的振幅越来越小,和围岩上...     

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。     

低速带的波场数值模拟及影响因素初步分析

低速带具有“自由表面、低速度、高吸收”的特征,能引起反射波能量减弱,产生很强的频散,造成近地表波场畸变,严重影响地震勘探的精度。而地震采集过程又不可避免遇到以下低速带问题:①低速带存在与否会对地震波传播造成什么影响;②近地表变化大,怎么才能得到精确的低速带参数;③存在低速带时,激发井深、最佳的药量(与子波频率有关)、最佳的耦合(与低速带速度相关)等采集参数会对采集资料的品质产生什么影响。本文通过数值模拟,集中对低速带与地震波激发的井深、速度、子波主频等核心采集参数的关系进行分析研究,同时在低速带背景下对数值模拟的网格、边界等问题也进行了讨论。模拟得到的波场特征及低速带参数影响的机理分析,对做好野外地震波激发,获取高品质的地震资料,具有理论意义和指导作用。      

断层场地地震反应特征研究

如何合理评价断层场地对地震动影响进而为重大工程抗震设计提供依据是当前急需解决但尚未解决好的工程场地问题。针对根据工程经验抽象出的8种设想断层场地模型，应用显式有限元模拟计算了脉冲P波、SV波倾斜入射下的地震反应。根据数值模拟结果，总结和给出了断层倾向、破碎带宽度、破碎带形态对地震动影响的初步定量规律。     

Guided Waves from Sources Outside Faults: An Indication for Shallow Fault Zone Structure?

— Using 3-D numerical modeling of seismic wave propagation we investigate the possibility of generating fault zone (FZ) trapped wave energy from sources well outside a fault. The FZ is represented by a O(200 m) wide vertical low velocity layer in a half space. We find that FZ trapped waves can be excited from sources well outside the fault if (1) the low-velocity structure extemds only to shallow depth and the source is located at greater depth or (2) the structure of the low-velocity zone is such that only the shallow part of the FZ traps energy. FZ trapped waves are not excited from sources well outside a FZ continuous with depth. The results support, in conjunction with recent observational evidence, a model for natural faults with shallow trapping structures rather than ones that span the entire seismogenic zone. This may have implications for fault mechanics as well as for aspects of shaking hazard near faults.     

Numerical Simulation of Fault Zone Guided Waves: Accuracy and 3-D Effects

-- Fault zones are thought to consist of regions with reduced seismic velocity. When sources are located in or close to these low-velocity zones, guided seismic head and trapped waves are generated which may be indicative of the structure of fault zones at depth. Observations above several fault zones suggest that they are common features of near fault radiation, yet their interpretation may be highly ambiguous. Analytical methods have been developed to calculate synthetic seismograms for sources in fault zones as well as at the material discontinuities. These solutions can be used for accurate modeling of wave propagation in plane-parallel layered fault zone structures. However, at present it is not clear how modest deviations from such simplified geometries affect the generation efficiency and observations of trapped wave motion. As more complicated models cannot be solved by analytical means, numerical methods must be employed. In this paper we discuss 3-D finite-difference calculations of waves in modestly irregular fault zone structures. We investigate the accuracy of the numerical solutions for sources at material interfaces and discuss some dominant effects of 3-D structures. We also show that simple mathematical operations on 2-D solutions generated with line sources allow accurate modeling of 3-D wave propagation produced by point sources. The discussed simulations indicate that structural discontinuities of the fault zone (e.g., fault offsets) larger than the fault zone width affect significantly the trapping efficiency, while vertical properly gradients, fault zone narrowing with depth, small-scale structures, and moderate geometrical variations do not. The results also show that sources located with appropriate orientations outside and below a shallow fault zone layer can produce considerable guided wave energy in the overlying fault zone layer.     

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.     

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.     

SEISMIC MODELLING WITH CHANNEL WAVES IN SEAM STRUCTURES INFLUENCED BY MYLONITE ZONES1

Channel waves generated in coal-seams and their reflections from discontinuities are widely used to indicate the tectonic and stratigraphic features of coal deposits, resulting in greater efficiency and safety in coal-mining. In the mining area of Ibbenbüren (F.R.G.) seam structures sometimes contain so-called mylonite zones, which are crushed coal deposits capable of binding gas. If mining hits a mylonite zone this would probably not only reduce output of the mine, but could even cause gas explosions. To investigate the influence of a mylonite zone on the propagation of channel waves, Rayleigh channel wave measurements for 2D analogue models were performed and synthetic seismograms of Love channel waves were calculated. Analogue modelling of the mylonite zone using Rayleigh seam waves within the seam was carried out using a perforation technique. Calculations were made to obtain an estimate of velocity reduction due to perforation. The results agree well with velocity values measured up to a perforation of 25% in a 2D epoxy resin model. Reflected channel wave energy was found by applying dispersion analysis in the case where the impedance reduction between the mylonite seam structure and the undisturbed seam was approximately 5%. The horizontal width of the mylonite structure was detectable from the time lag between reflected channel wave signals from both in-seam borders of the mylonite zone. Resolution of two discrete borders was possible for a width of 1.5 λ's. The influence of a vertical fault, positioned within the mylonite zone, could only poorly be resolved. Numerical model investigations of Love seam waves were concerned mainly with the variation of the horizontal width of the mylonite zone. Mylonite zones with dimensions of the order of 0.4 λ's allow definite statements about their widths from dispersion and spectral analyses. For zones with smaller widths down to 0.2 λ's, it was found that reflectivity and transmissivity analyses give a qualitative criterion for distinguishing a mylonite structure surrounding a fault from a pure fault.     

Numerical study of seismic scattering and waveguide excitation in faulted coal seams

Finite‐difference P‐SV simulations of seismic scattering characteristics of faulted coal‐seam models have been undertaken for near‐surface P‐ and S‐wave sources in an attempt to understand the efficiency of body‐wave to channel‐wave mode conversion and how it depends on the elastic parameters of the structure. The synthetic seismograms clearly show the groups of channel waves generated at the fault: one by the downgoing P‐wave and the other by the downgoing S‐wave. These modes travel horizontally in the seam at velocities less than the S‐wavespeed of the rock. A strong Airy phase is generated for the fundamental mode. The velocity contrast between the coal and the host rock is a more important parameter than the density contrast in controlling the amplitude of the channel waves. The optimal coupling from body‐wave energy to channel‐wave energy occurs at a velocity contrast of 1.5. Strong guided waves are produced by the incident S‐sources for source angles of 75° to 90° (close to the near‐side face of the fault). As the fault throw increases, the amplitude of the channel wave also increases. The presence of a lower‐velocity clay layer within the coal‐seam sequence affects the waveguiding characteristics. The displacement amplitude distribution is shifted more towards the lower‐wavespeed layer. The presence of a ‘washout’ zone or a brecciated zone surrounding the fault also results in greater forward scattering and channel‐wave capture by the coal seam.     

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.     

断层带震相及其应用研究现状与展望

Deep structure and material properties of faults can be understood by observing and simulating the particular phase in a fault fracture zone. This paper reviews the development of fault-zone seismic waves in the seismological domain. The present research status of fault-zone head wave and trapped wave are summarized systematically. Based on recent progress in this field, the paper discusses the prospect on the utilization of seismic wave in fault structure research.     

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…