共查询到19条相似文献,搜索用时 187 毫秒
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中国大陆地壳厚度的特点是东部地区薄西部地区厚,因此在计算Pnl波的Green函数时进一步考虑了莫霍界面倾斜的影响.本文将广义射线理论推广到倾斜层结构模型,该方法的计算结果与有限差分的计算结果有很好的一致性.理论计算表明,在同一个倾斜结构模型中沿相反方向传播的Pnl波有明显的差异.因此当地壳厚度的变化不能忽略时,根据水平层模型的理论计算结果拟合Pnl波记录时效果不够理想.对菏泽、门源地震资料的处理结果表明,用一个更接近实际地壳的倾斜层模型来拟合Pnl波比用等效厚度平行层模型来拟合要更为合理. 相似文献
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本文用波形拟合方法,对中国西北地区四个中强地震的Pnl波进行了研究,获得了这些地震的断层面解、震源时间函数、地震矩等参数。我国地震台网所记录到的国内地震大部分落在3—13°的范围内,因此在此范围内的Pnl波对研究区域应力场,板块动力学及地壳结构具有非常重要的意义。 相似文献
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利用气枪地震资料研究燕山隆起带南部地区地壳S波速度及泊松比结构 总被引:4,自引:0,他引:4
泊松比是了解地球内部介质的一个重要参数,在地震学上可以通过P波和S波速度的比值来确定.但是传统人工地震测深采用的炸药等爆破源产生的S波较弱,难以用来研究泊松比结构.对2006年河北省遵化市上关湖水库大容量气枪试验产生的地震数据进行研究,发现气枪震源能够有效地产生S波.根据偏振分析,认为S波主要是气枪产生的P波在水库底部固液界面转换产生的.波形拟合能够充分利用波形和走时信息,是研究地下结构的一种有效的方法.对气枪产生的S波进行波形拟合,获得了燕山隆起带南部地区地壳的S波速度模型,并对比修正后的P波速度模型,进一步得到了该地区的泊松比结构.研究表明:1)该地区的地壳厚度约为33km.2)该地区地壳整体泊松比值偏低,上(0~14km)中(14~28km)下(28~33km)地壳以及上地幔顶部(33km附近)的泊松比平均值分别为0.25,0.25,0.27,0.27.上地壳和中地壳可能以长英质的酸性岩石为主,下地壳和上地幔顶部可能以铁镁质的基性岩石和中性岩石为主.3)该地区上下地壳各存在一个低速层,它们可能主要是流体作用的结果. 相似文献
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本文根据1982和1985年在福州—泉州—汕头地区的人工爆炸地震测深资料,分析了震相特征,共识别到九个波组:P1、Pg、Pg′、P3°、P4(P4°)、P5°、Pn(Pn°)、P7*及S波组。通过对波的走时反演、正演拟合、理论地震图和射线追踪方法反复计算,得到了该区地壳与上地幔结构模型。结果表明,该区具有大陆地壳向海洋地壳过渡的边缘地区结构特征。地壳P波速度6.30km/s,莫霍面速度7.90km/s,地壳厚度30km,由三层构成,厚度分别为3km、15km和12km。在中地壳存在一层速度为5.50—5.90km/s、厚度为3.0—4.0km的低速层,低速层分布与温泉出露有密切的关系。在下地壳下部有一数公里厚的高速致密的壳-幔混合物层,其形成原因是由于上地幔物质上涌并迁移到下地壳的结果。此外,还讨论了莫霍面结构,界面起伏和断裂展布概况。 相似文献
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利用纯S波波形拟合方法,输入纯S波波形,使用传递矩阵计算了层状介质自底面传到地表约100 km厚度、32 s的理论地震波形;引进快速模拟退火法进行反演搜索理想模型,用理论波形与观测波形的相关系数作为约束函数,选择同一台站几个震例的理论波形与实际波形吻合最好的模型作为该台站下方的可接受速度结构模型.收集深源远震的清晰S波记录波形,我们共得到了陕西省境内秦岭造山带中段及其邻近区域13个地震台站下方的S波速度结构.结果显示,秦岭造山地带、渭河盆地及鄂尔多斯块体的地壳结构之间存在很大的差异,各个块体有其各自的构造特点;不过三个块体的地壳厚度都显示了由东向西逐渐增加的变化趋势. 相似文献
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地壳厚度、波速比或泊松比是研究地壳结构和性质的基本地震学参数,对于研究地壳组分特征及构造演化具有重要意义.经典H-κ叠加方法是利用远震接收函数资料求取台站下方地壳厚度和波速比最为简便高效的方法.但该方法隐含着Moho面是水平界面的假设条件,意味着Ps转换波及后续多次波相对P波的走时主要取决于地壳厚度和纵横波速度,而忽略了界面产状的影响.理论模拟表明,如果不考虑Moho面的产状,特别是在Moho面倾角较大的情况下,利用经典H-κ叠加方法得到的地壳厚度和波速比会偏离实际模型,尤其会造成波速比的过高估计,从而影响到对地壳结构和性质的认知.为了解决Moho面倾斜条件下的地壳厚度和波速比求取问题,本文推导了界面倾斜条件下Ps转换波与后续多次波相对于直达P波的理论到时公式;基于经典H-κ叠加方法的思想,提出了一种可以同步求取地壳厚度-波速比-Moho面倾角的H-κ-θ叠加方法.通过理论模型测试,验证了该方法具备较高的稳定性和可靠性,并将此方法应用于青藏高原南部Hi-CLIMB台阵资料,显示出较好的应用潜力. 相似文献
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根据安徽台网25个台站记录到的远震波形资料,运用频率域反褶积的方法提取接收函数,并采用H-Kappa扫描法反演得到安徽地区各个台站下方的地壳厚度与纵横波速度比。结果显示,安徽地区台站下方地壳厚度大致可分为3个区域:皖西南大别山地区、皖南山区和淮河以北的皖北平原地区,其中大别山地区台站下方的地壳厚度位于35—39 km范围内,相对较厚;皖南地区位于33—36 km范围内;皖北以平原为主,地壳厚度位于30—33 km范围内。这一研究结果与安徽地区的地质构造背景具有较好的相关性。同时,H-K扫描结果显示,安徽地区台站下方波速比基本处于1.70—1.80范围内,变化不大。在界面倾斜角度不大的前提下,利用横向均匀分层模型的波形反演实现接收函数的波形拟合,得到台站下方地壳上地幔S波速度结构,计算结果显示,安徽地震监测台站下莫霍面上表面S波速度一般为3.6—3.9 km/s,而界面底部大约为4.3—4.6 km/s,莫霍面处的速度起伏变化并不十分明显。 相似文献
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由深源远震体波记录反演华北北部地壳上地幔速度结构 总被引:5,自引:2,他引:5
重点研究的地区为河北省北部包括京津地区,以及山西、内蒙的部分地区,在此区选取了29个台站;在向东延伸的背景区,选取了6个台站。利用这些台站的深源远震体波记录资料,通过选取介质结构模型,计算理论地震图,与观测图进行拟合,以确定地震台下介质结构的可接受模型。在拟合时,对每个地震台站都选择若干次深源远震的体波记录作为观测图。对每个地震台站一般都算出60个不同模型的理论图。实际上做出的结果比地壳深,为大约80km(即大致相当于岩石层或称岩石圈)厚度内的地壳上地幔介质结构,它们大都由10层左右的介质组成。通过波形拟合共给出了上述35个台站下的壳幔介质分层结构。并由此给出了Moho面的轮廓。 相似文献
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Hengchang Dai 《Geophysical Prospecting》2003,51(4):347-364
Shear waves recorded at or near the sea-bed, i.e. a water–sediment interface, may suffer from unwanted phase change, which is detrimental to velocity analysis and processing and degrades the quality of the final stacked or migrated image. In this study, this phenomenon is analysed for P-SV converted waves recorded at the sea-bed. Theoretical analysis shows that phase change does not occur if the converted shear waves always maintain raypaths that lie within the critical angle, provided the subsurface layering is horizontal. A phase change that is asymmetric with offset can readily be explained as being due to dipping layers at targets or the dipping sea-bed. This analysis is extended to multiple layers and anisotropic media and shows that the same conclusions hold. The analysis performed on two sets of ocean-bottom-cable seismic data shows that the majority of observations show little evidence of phase change, and occasionally display the asymmetric phase change with offset. This finding underlines the robustness of converted shear waves for imaging the horizontal subsurfaces and sea-bed as all of the offset information may be used. 相似文献
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本文利用秦岭周边和南美地区的部分台站2012-2014年记录的地震事件垂直分量数据,获取了166个台站对之间的互相关函数,从中观测到了近对跖点台站之间的体波格林函数.在此基础上,我们计算了理论地震图的互相关,其结果与实际数据获得的结果很相似,推测格林函数的能量来源应主要是大地震引起的地球自由振荡.更进一步的研究表明,不同的震源机制对于互相关结果中不同震相的振幅有较大影响,走滑断层引起的地震并不能产生较好的互相关结果.通过对比不同位置台站对的互相关结果,本文认为互相关得到的体波格林函数包含了传播路径信息. 相似文献
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使用接收函数研究壳幔速度间断面和速度结构已是常用的技术,但介质各向异性或倾斜的莫霍(Moho)界面,都会造成接收函数波形的复杂性。本文利用远震P波接收函数计算台站下方的地壳各向异性,通过信噪比测试和谐波分析两种方法来验证各向异性结果的可靠性。通过甘肃地震台网的两个台站记录,讨论各向异性和倾斜界面对接收函数的影响,结果显示,台站BYT(白银)下方具有各向异性,而台站WYT(渭源)下方由于可能存在倾斜界面,得到的各向异性结果则有待进一步分析。为了更好地认识倾斜界面对各向异性计算结果的影响,采用合成理论地震图,计算接收函数,然后利用合成接收函数进行各向异性分析。结果表明,计算得到的快波方向不会受到倾斜界面的影响,但是时间延迟会受到影响。 相似文献
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This study used SKS waveforms from the International Deep Profiling of Tibet and the Himalayas (INDEPTH) III dataset and a new 2D method for modeling seismic waves in anisotropic media to construct an image of anisotropic structures beneath central Tibet. A preferred model revealed three-segment anisotropic structures in the upper mantle beneath the study region. Waveform modeling demonstrated that the anisotropy was mainly generated by the lithosphere but not the asthenosphere, and that an anisotropic model with a flatter axis of symmetry provides a more consistent interpretation of the observations than models having steeply dipping symmetry axes. A relatively low velocity zone may underlie or intermingle with the anisotropic structures in the northern portion of the region. Synthetic tests also indicate that variations in the elastic constants and depth extent of the anisotropy assumed by the calculations do not affect the general conclusions, although trade-offs exist among certain model parameters. The modeling results suggest that the complex seismic structures in central Tibet were associated with underthrusting of the Indian lithosphere beneath the Asian lithosphere; the inferred flat symmetry axis of the anisotropy was likely generated during this collision process. If this were not the case, the inherited anisotropy would exhibit a steeply dipping axis of symmetry, parallel to the direction of underthrusting. 相似文献
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For converted waves, stacking as well as AVO analysis requires a true common reflection point gather which, in this case, is also a common conversion point (CCP) gather. The coordinates of the conversion points for PS or SP waves, in a single homogeneous layer can be calculated exactly as a function of the offset, the reflector depth and the ratio vp/vs. An approximation of the conversion point on a dipping interface as well as for a stack of parallel dipping layers is given. Numerical tests show that the approximation can be used for offsets smaller than the depth of the reflector under consideration. The traveltime of converted waves in horizontal layers can be expanded into a power series. For small offsets a two-term truncation of the series yields a good approximation. This approximation can also be used in the case of dipping reflectors if a correction is applied to the traveltimes. This correction can be calculated from the approximated conversion point coordinates. 相似文献
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通过在青藏高原东北缘设计专门的三维地震观测系统而获得的莫霍界面反射波,利用三维反演方法反演重建了该区莫霍(M)界面的构造形态,得到了研究区M界面的三维构造图像和地壳深断裂的展布,研究区M界面总体上由东北向西南方向呈逐渐下倾趋势,而在不同的块体内部又具有不同的倾斜态势,反映了不同块体之间的差异和复杂程度的不同.鄂尔多斯块体M界面变化平缓,内部结构完整且坚硬;弧形构造区M界面的倾斜趋势发生了逆转,此现象可视为该区域在挤压、变形构造作用下M界面发生了明显的扭曲变形;秦祁块体M界面呈现出较陡的倾斜趋势,在本块东南端与弧形区结合部,M界面所显示出的局部隆起可视为地壳发生了强烈扭曲变形的迹象.综合二维、三维结果认为,特殊而复杂的构造变形环境,为海原8.6级大地震的孕育和发生提供了地质条件和深部背景. 相似文献
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J. D. LASKI 《Geophysical Prospecting》1978,26(1):48-81
A method to compute the parameters of a multilayered medium with dipping interfaces is described. The input data are time-distance curves of diving waves. The output data are the thickness of the layers, dips, and parameters characterizing the increase of velocity with depth. Three examples are presented. 相似文献
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In this work, we develop the indirect boundary element method (IBEM) to simulate the seismic site response in a realistic, large-scale 3-D sedimentary basin. Most previous applications of boundary element method have used full-space Green’s functions for wave propagation between element points. We use half-space Green’s functions, which include the seismic wavefield interactions at the free surface and require only the boundary elements of the basin interface. In this way, the size of the matrix equation for solution in the IBEM can be reduced to approximately a quarter of that using full-space Green’s functions. The site response modeling of the Granada basin in southern Spain using the IBEM shows that the basin-induced scattering waves were identified as propagating back and forth inside the basin. The scattered waves also generate surface waves that are weakly propagated outside of the basin. The wave propagation inside and outside of the basin shows different patterns. We observe that the scattered wave is locally amplified, and its propagation direction deviates from that of the incident waves propagation direction. Therefore, the computed seismic response in the basin could provide us with good estimates of the seismic motion. 相似文献
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Receiver functions of teleseismic waveforms recorded at four Hungarian permanent broadband stations have been analyzed using
semilinearized and stochastic inversion methods to estimate the crustal thickness and S wave velocity structure in the Pannonian
Basin. The results of both inversion methods agree well with the crustal thicknesses obtained by previous seismic refraction
and reflection studies in the regions which are densely covered with seismic lines (28 and 27 km in westernmost and southern
Hungary, respectively) and suggest a thicker crust compared to what was known before beneath the Transdanubian and Northern
Ranges (34 and 33 km, respectively). The comparison of the one-dimensional shear wave velocity models derived by the different
inversion methods shows that, in case of simple, smoothly varying structures, the results do not differ significantly and
can be regarded as absolute velocities. Otherwise, the recovered velocity gradients agree, but there are differences in the
absolute velocity values. The back-azimuthal variations of both radial and tangential receiver functions are interpreted as
dipping structure and as waves sampling different geological areas. The signature of the deep structure on low-frequency receiver
functions suggests a strong velocity contrast at the 670-km discontinuity. The vanishing 410-km boundary may be attributed
to the remnant of a subducted oceanic slab with increased Poisson’s ratio in the transition zone. 相似文献