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震源定位是微地震监测技术要解决的主要问题.目前,井下微地震监测多采用走时拟合法计算震源位置.常规方法受到环境噪声、初至拾取误差、速度模型误差等因素的影响,定位结果存在一定误差.为了提高定位精度,本文提出了一种改进的基于网格搜索的微地震震源定位方法.本文方法根据P波的偏振特征参数计算概率密度函数求取震源方位角,并采用改进的目标函数和搜索算法计算震源的径向距离和深度.模型数据和实际资料的处理结果表明,本文方法具有较强的抗噪性,计算得到的震源方位角更加接近真实值;与常规目标函数相比,本文方法采用的目标函数具有更好的收敛性,其定位结果受初至拾取误差和速度模型误差的影响更小;本文提出的搜索算法能够消除由于错误拾取造成的观测到时中的异常值对定位结果的影响. 相似文献
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地震定位是地震监测与减灾研究重要基础.基于均匀或横向均匀介质模型,利用震源轨迹确定震源位置的交切法具有稳健和效率高的优点,但定位精度较低,特别是震源深度.为提高震源定位精度,我们提出适用于三维复杂速度模型的地震定位交切法.将地壳速度模型由均匀或横向均匀介质模型扩展为三维复杂速度模型;均匀或横向均匀介质模型对应的原假设为球面或双曲面的震源轨迹通过最小走时树射线追踪技术予以确定.确定震源位置的震源轨迹以到时差作为约束条件;将震源定位于震源轨迹交汇最密集的点处,即总的到时差残差(RDT)最小的点处.定位结果的不确定性可通过RDT值较小节点的空间分布予以定性表示.考察了准确速度模型、扰动速度模型、扰动观测到时及地震在台网外等4种情况下改进方法的地震定位效果,结果表明改进的交切法可用于三维复杂速度模型的地震定位;综合利用P波与S波的到时差信息,可明显改善震源位置约束;使用多条震源轨迹进行定位,有助于减少由随机因素导致的定位误差. 相似文献
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近震震源深度测定精度的理论误差分析 总被引：3，自引：1，他引：2
震源深度是地震学中最难准确测定的参数之一,各种方法对于震源深度的估计都具相当程度的不确定性,影响着人们对震源过程的认识。各种因素对震源深度的影响是非线性的,本文从近震走时公式入手,分析了震中距、到时残差和速度模型(地壳模型)对震源深度的影响。当地震波传播速度一定时,震源深度的误差随着震中距或台站距离的增大和走时残差的增大而增大。走时残差一定时,震源深度误差随着震中距的增大和地震波速度的增大而增大。研究也表明,当速度已知,走时残差一定时,越浅的地震,定位误差可能越大。定位精度产生的水平误差随着震中距、走时误差和地震波速度的增大而增大,震源深度误差也将增大。另外,震源深度的误差会导致发震时刻的变化,随之而来的结果都会因此而改变。 相似文献
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基于偏移成像的微地震定位方法由于可避免走时拾取误差以及可实现自动化定位等优点被广泛应用.绕射叠加方法将能量沿走时曲线聚焦到空间网格点上,进行成像时需要搜索发震时刻.干涉成像方法利用互相关提取的走时差信息可避免搜索发震时刻,但定位结果受数据信噪比的影响较大.为了进一步提高干涉成像法的定位精度,本文提出一种同时使用互相关和自相关道集的全干涉成像方法,增加的自相关道集提取的S-P走时差可降低震源-检波器方向的定位误差,提高定位精度.单井监测的理论测试和实际数据的研究结果表明,全干涉成像的定位精度高于仅使用互相关道集的干涉成像方法,同时计算效率高于绕射叠加方法. 相似文献
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内蒙古中西部一维均匀地壳速度模型研究 总被引：1，自引：1，他引：0
《地震地磁观测与研究》2015,(4)
使用内蒙古地震台网记录的内蒙古中西部59个地震,使用单纯型方法和Pn/Pg联合测定深度方法,对震中和震源深度重新测定,提取定位结果的纵波走时数据。使用理论走时公式,将已知变量和未知变量分离建立方程组,使用共轭梯度法,反演得到包含5个参数的两层均匀速度模型。使用Hyposat方法,对比新模型和现有模型的定位残差,新模型残差有所降低,震源深度控制较好。 相似文献
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近场震源的高精度定位在工程建设与军事应用等方面意义重大且应用广泛,如炮弹落点定位或车辆追踪等.定位过程面临速度结构未知、高分辨率要求等问题,传统的震源定位方法有一定的局限性.本文将超声波检测中的时差分布图(Delta T Mapping,简称DTM)方法首次成功引入近场震源定位问题中.DTM定位法首先建立一个测区的到时差模型,然后基于此模型对新的震源进行定位.有两种建立模型的方法,(1)网格搜索法:对原有模型进行线性插值,得到更高分辨率的到时差分布模型;(2)统计定位法:利用高斯过程回归建立到时差数据与位置坐标之间的映射关系.本文在北京某郊区进行了炸点定位实验,在140 m×90 m的测试区域内,定位误差为0.5~5.1 m.结果表明,DTM方法是一种可靠、高精度、具有近实时性的近场震源定位方法.进一步利用接收点、源点互换,在获得高精度DTM同时,可大幅降低标定与数据分析成本.结合震源扫描法具有解决多目标定位问题的潜力. 相似文献
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《地球物理学报》2021,64(7)
区域和全球地震定位越来越多地基于更接近实际的横向非均匀速度模型.速度模型主要来自于地震体波层析成像结果,分辨率不是很高.这样,模型宜于以稀疏网格剖分以减少计算时间和计算机内存需求.当剖分的模型单元较大时,基于射线追踪技术计算复杂介质地震定位中震源轨迹的方法——选取震源轨迹所经过单元节点(位于单元中心,称为震源轨迹节点)为轨迹参考点,利用最小走时树射线追踪方法计算绝对残差场中连接轨迹参考点的射线路径作为震源轨迹——计算结果误差较大,难以满足精定位需要.针对该问题,本文对其进行了改进:不将震源轨迹节点作为轨迹参考点,而是基于插值技术计算每个轨迹节点其法线点对(即该节点与其周围残差正负极性不同的相邻节点组成的点对中梯度绝对值最大的那对)间残差为零的点作为震源轨迹参考点.算例表明:和原方法相比,改进方法计算的震源轨迹更为精细,计算精度提高数十(线性插值)至数百倍(非线性插值),而计算效率基本保持在同一数量级,使利用震源轨迹进行直观、快速和高精度的区域或全球地震事件定位成为可能;壳幔界面反射纵波(PmP)对震源的约束和直达纵波(Pg)相似;同一台站PmP-Pg波到时差约束的震源轨迹对震源深度有很好的约束. 相似文献
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在地震定位中常常需要求解震源轨迹,但由于复杂介质中的震源轨迹较为复杂,难以给出其解析解,因此震源轨迹的计算通常仅限于简单介质模型.本文基于最小走时树射线追踪技术,提出了一种计算复杂介质中震源轨迹的方法.为回避发震时间问题,以观测到时差作为震源轨迹的约束条件.首先从模型节点中选出少量理论到时差与观测到时差之绝对差,即双重时差较小的点作为震源轨迹的代表点,然后以其中双重时差最小的点为初始点,在双重时差场中利用最小走时树射线追踪方法计算出初始点到其他震源轨迹代表点的射线路径作为震源轨迹.当选的震源轨迹代表点较多时,得到的震源轨迹较为粗略,此时可去掉射线经过次数较少的代表点的射线路径使震源轨迹更为精细.为减少计算量,对最小走时树射线追踪方法的终止条件做了修正.以一个复杂介质模型中的地震为例,计算了包括速度扰动、到时扰动等不同情况下的震源轨迹,结果表明所提出的震源轨迹计算方法切实可行. 相似文献
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Cross double‐difference inversion for simultaneous velocity model update and microseismic event location 
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下载免费PDF全文 Microseismic monitoring is an approach for mapping hydraulic fracturing. Detecting the accurate locations of microseismic events relies on an accurate velocity model. The one‐dimensional layered velocity model is generally obtained by model calibration from inverting perforation data. However, perforation shots may only illuminate the layers between the perforation shots and the recording receivers with limited raypath coverage in a downhole monitoring problem. Some of the microseismic events may occur outside of the depth range of these layers. To derive an accurate velocity model covering all of the microseismic events and locating events at the same time, we apply the cross double‐difference method for the simultaneous inversion of a velocity model and event locations using both perforation shots and microseismic data. The cross double‐difference method could provide accurate locations in both the relative and absolute sense, utilizing cross traveltime differences between P and S phases over different events. At the downhole monitoring scale, the number of cross traveltime differences is sufficiently large to constrain events locations and velocity model as well. In this study, we assume that the layer thickness is known, and velocities of P‐ and S‐wave are inverted. Different simultaneous inversion methods based on the Geiger's, double‐difference, and cross double‐difference algorithms have been compared with the same input data. Synthetic and field data experiments suggest that combining both perforation shots and microseismic data for the simultaneous cross double‐difference inversion of the velocity model and event locations is available for overcoming the trade‐offs in solutions and producing reliable results. 相似文献
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V.B. Piip 《Geophysical Prospecting》2001,49(4):461-482
A method using simple inversion of refraction traveltimes for the determination of 2D velocity and interface structure is presented. The method is applicable to data obtained from engineering seismics and from deep seismic investigations. The advantage of simple inversion, as opposed to ray‐tracing methods, is that it enables direct calculation of a 2D velocity distribution, including information about interfaces, thus eliminating the calculation of seismic rays at every step of the iteration process. The inversion method is based on a local approximation of the real velocity cross‐section by homogeneous functions of two coordinates. Homogeneous functions are very useful for the approximation of real geological media. Homogeneous velocity functions can include straight‐line seismic boundaries. The contour lines of homogeneous functions are arbitrary curves that are similar to one another. The traveltime curves recorded at the surface of media with homogeneous velocity functions are also similar to one another. This is true for both refraction and reflection traveltime curves. For two reverse traveltime curves, non‐linear transformations exist which continuously convert the direct traveltime curve to the reverse one and vice versa. This fact has enabled us to develop an automatic procedure for the identification of waves refracted at different seismic boundaries using reverse traveltime curves. Homogeneous functions of two coordinates can describe media where the velocity depends significantly on two coordinates. However, the rays and the traveltime fields corresponding to these velocity functions can be transformed to those for media where the velocity depends on one coordinate. The 2D inverse kinematic problem, i.e. the computation of an approximate homogeneous velocity function using the data from two reverse traveltime curves of the refracted first arrival, is thus resolved. Since the solution algorithm is stable, in the case of complex shooting geometry, the common‐velocity cross‐section can be constructed by applying a local approximation. This method enables the reconstruction of practically any arbitrary velocity function of two coordinates. The computer program, known as godograf , which is based on this theory, is a universal program for the interpretation of any system of refraction traveltime curves for any refraction method for both shallow and deep seismic studies of crust and mantle. Examples using synthetic data demonstrate the accuracy of the algorithm and its sensitivity to realistic noise levels. Inversions of the refraction traveltimes from the Salair ore deposit, the Moscow region and the Kamchatka volcano seismic profiles illustrate the methodology, practical considerations and capability of seismic imaging with the inversion method. 相似文献
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本文介绍了根据反射地震数据进行波速成象的一种方法,其基础为多种反演技术的综合。由于要求的波速图象C（x,z）具有间断性,除利用走时数据T（x,t）外,在地层比较水平的情况下,还利用了均方根速度V（x,t）和统计子波W（t）的数据来成象。计算机层析成象过程分为三步:首先重做速度分析,取得与初次反射走时一致的均方根速度数据;然后用反射走时与均方根速度联合反演对应分析道的层速度和界面深度;最后由联合反演结果和反射面走时求波速图象函数的数字化版。文中还给出了波速成象方法在我国西北某沉积盆地上的应用及验证结果。 相似文献
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地震波的运动学信息(走时、斜率等)通常用于宏观速度建模.针对走时反演方法,一个基本问题是走时拾取或反射时差的估计.对于成像域反演方法,可以通过成像道集的剩余深度差近似计算反射波时差.在数据域中,反射地震观测数据是有限频带信号,如果不能准确地确定子波的起跳时间,难以精确地确定反射波的到达时间.另一方面,如果缺乏关于模型的先验信息,则很难精确测量自地下同一个反射界面的观测数据同相轴和模拟数据同相轴之间的时差.针对走时定义及时差测量问题,首先从叠前地震数据的稀疏表达出发,利用特征波场分解方法,提取反射子波并估计局部平面波的入射和出射射线参数.进一步,为了实现自动和稳定的走时拾取,用震相的包络极值对应的时间定义反射波的到达时,实现了立体数据中间的自动生成.理论上讲,利用包络极值定义的走时大于真实的反射波走时,除非观测信号具有无限带宽(即delta脉冲).然而,走时反演的目的是估计中-大尺度的背景速度结构,因此走时误差导致的速度误差仍然在可以接受的误差范围内.利用局部化传播算子及特征波聚焦成像条件将特征波数据直接投影到地下虚拟反射点,提出了一种新的反射时差估计方法.既避免了周期跳跃现象以及串层等可能性,又消除了振幅因素对时差测量的影响.最后,在上述工作基础之上,提出了一种基于特征波场分解的新型全自动反射走时反演方法(CWRTI).通过对泛函梯度的线性化近似,并用全变差正则化方法提取梯度的低波数部分,实现了背景速度迭代反演.在理论上,无需长偏移距观测数据或低频信息、对初始模型依赖性低且计算效率高,可以为后续的全波形反演提供可靠的初始速度模型.理论和实际资料的测试结果证明了本文方法的有效性. 相似文献
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初至波走时层析反演技术作为建立近地表速度模型的重要手段,是解决陆地资料复杂静校正问题的关键技术。而折射波广泛发育的海洋地震资料,对折射波信息的关注与运用并没有得到广泛的重视。本文首次将层析反演方法应用于海洋拖缆地震数据的近海底速度模型的建立。本文方法与陆地资料层析反演的主要区别在于:①在震源信号的最小相位化处理后进行初至时间的拾取,避免了混合相位子波初至拾取不准带来的误差;②以海水深度与海水速度作为反演约束条件,减小了迭代误差。实测二维资料的层析反演结果表明,本文方法可反演出较为精确的海洋地层速度结构。 相似文献
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Compaction induced by pore‐pressure decrease inside a reservoir can be monitored by measuring traveltime shifts of reflection events on time‐lapse seismic data. Recently we introduced a perturbation‐based formalism to describe traveltime shifts caused by the 3D stress‐induced velocity field around a compacting reservoir. Application of this method to homogeneous background models showed that the offset variation of traveltime shifts is controlled primarily by the anisotropic velocity perturbations and can provide valuable information about the shear and deviatoric stresses. Here, we model and analyse traveltime shifts for compacting reservoirs whose elastic properties are different from those of the surrounding medium. For such models, the excess stress is influenced primarily by the contrast in the rigidity modulus μ across the reservoir boundaries. Synthetic examples demonstrate that a significant (25% or more) contrast in μ enhances the isotropic velocity perturbations outside the reservoir. Nevertheless, the influence of background heterogeneity is mostly confined to the reservoir and its immediate vicinity and the anisotropic velocity changes are still largely responsible for the offset dependence of traveltime shifts. If the reservoir is stiffer than the host rock, the background heterogeneity reduces anisotropic velocity perturbations inside the reservoir but increases them in the overburden. As a result, in this case, the magnitude of the offset variation of traveltime shifts is generally higher for reflections from interfaces above the reservoir. We also study compaction‐induced stress/strain and traveltime shifts for a stiff reservoir embedded in a softer layered model based on velocity profiles from the Valhall Field in the North Sea. Despite producing discontinuities in strain across medium interfaces, horizontal layering does not substantially alter the overall behaviour of traveltime shifts. The most pronounced offset variation of traveltime shifts is observed for overburden events recorded at common midpoints close to the reservoir edges. On the whole, prestack analysis of traveltime shifts should help better constrain compaction‐induced velocity perturbations in the presence of realistic background heterogeneity. 相似文献
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