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1.
《中国科学:地球科学》2016,(1)
地下岩石普遍存在着非均匀性,当井孔周围岩石的非均匀体的尺度(如压裂产生的裂缝系统)与声波波长相当时,会产生很强的散射波,因此可以通过声波测井的散射效应评价地层的非均匀性.文章基于弹性介质散射体在统计意义上的分布规律,建立了三维井孔非均匀介质模型,数值模拟了非均匀地层偶极声波测井的散射效应,并分析了散射波的衰减特性.模拟结果表明:与均匀介质相比,井孔周围非均匀体产生了明显的散射,一个显著的特征是在直达波之后出现了较强的尾波,且尾波的频率随着时间逐渐降低.在此基础之上,根据尾波的衰减特性提出了一种利用散射效应评价地层非均匀性的方法,并将该方法应用于致密储层的压裂效果评价.应用结果表明压裂后偶极声波测井散射效应产生的尾波预示着井孔周围岩石的体积改造,可以用来评价致密储层压裂效果,这为今后利用声波测井资料评价非常规储层(如页岩储层)的压裂效果提供了一条新的思路. 相似文献
2.
地震波散射:理论与应用 总被引：4，自引：0，他引：4
传统的球面对称(或层状构造)地球模型正经历着一场革命。地球被揭示从地壳、地幔到地核到处都呈现多尺度的横向非均匀性。这些具有不同尺度的非均匀体对地震波具有不同的效应。速度和密度的非均匀体能改变波形,引起走时和振幅的起伏以及产生直达波的视衰减。地球岩石层的非均匀体还能产生P尾波、S尾波和Lg尾波等。核-幔边界附近的非均匀体能产生对PKP波的散射而成为PKIKP的前驱波,PKKP波的散射波可成为主震相自己的前驱波。近源和近台站的复杂构造可通过共振、散射来改变地震波形。粗糙地形或粗糙界面能造成体波和面波的耦合。地壳内规则排列的裂隙可产生有效各向异性而使S波分裂。由三维非均匀体所引起的地震波的变化,在广义上被称为地震波散射。近十多年来,由于高质量的高频数字地震资料的逐渐增多,对地震波散射的研究在急速发展并引起了越来越多的地震学家、工程学家和勘探地球物理学家的兴趣。本文综述了地震波散射的基本理论和在这一领域各方面的最新进展。其内容大致为:一、地球横向非均匀性的谱及各种散射态式二、地震波散射的研究方法1.理论研究(1)不连续非均匀介质的边界匹配方法(2)弱散射的微扰法(3)高频近似法(4)随机方法和非均匀体的统计特性2.数值模拟和物理模型试验3.野外观测三、弹性波散射的基本特征和标量波近似1.弹性波瑞雷散射2.弹性波瑞雷-甘斯散射3.随机介质的弹性波散射四.地震波散射的表现和应用1.透射起伏2.尾波产生及包络消减3.散射衰减4.核-幔边界附近的散射5.地表地形、近地表结构和深部构造引起的散射6.裂缝散射和有效各向异性7.散射和非线性。 相似文献
3.
雨海盆地是月球正面最大的撞击盆地之一,确定其月壳与上月幔精细三维结构,对研究月球“质量瘤”形成机制等科学问题具有重要意义.常用于反演月壳与上月幔结构的月震波方法受限于月震台站稀少,给出三维结果的空间分辨率不足.随着重力测量技术的发展,月球重力数据横向分辨率逐步提高,但存在垂向分辨率不足问题.鉴于此,本文采用重力多尺度分析方法来进行改善,以获取研究区域月壳与上月幔精细三维密度结构与壳幔界面深度.研究结果表明：雨海盆地内部存在一个顶部小、底部大的高密度物质体,其底部中心位置约为经度16°W,纬度42°N;雨海盆地壳幔界面存在明显上隆,且盆地内部上隆趋势不平滑,发现有类环状异变现象;雨海“质量瘤”可能是由内部高密度物质和壳幔上隆共同推动形成的;重力多尺度分析方法可以有效提升重力数据的垂向识别能力,获取更为精细的三维月壳与上月幔结构. 相似文献
4.
岩石的非线弹性响应在实验室中已被广泛地观测到，但在文献中却鲜有地震学研究方面的报道，尽管这是观测到这种特征的最自然的环境。由于难以获得非线性波传播问题的解析解，因此需要使用近似方法。显然，地震波在均匀的非线弹性介质中传播时将受到非线性的扰动。这种扰动可看作是时空中初至波能量散射和传播、产生地震尾波之源。这在某种意义上类似于非均匀性效应。由非线性引起的地震尾波性质与非线性大小以及地震矩有关。我们使用一种扰动方法计算散射波的振幅，并说明该方法能相当好地描述实际地震尾波的主要特征。 相似文献
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7.
利用首都圈地震数字台网2009年1月至2016年3月记录的地震波形资料,采用Sato尾波单次散射模型,固定尾波窗长,计算唐山地区尾波Q值,时间和空间上分析Q值分布特征,结果显示,Q值在空间分布上呈现明显的横向不均匀性,在较长孕震时间上呈现降低—升高—降低—发震的过程,且中强震易发生在Q值高低值交界区偏高值一侧,震群易发生在Q值相对较低区域。 相似文献
8.
北京地区尾波衰减的研究 总被引：4，自引：1，他引：4
Aki(1969)提出了单次反向散射模式,该模式认为,尾波是由许多随机分布的不均匀体产生的单次反向散射波叠加而成的,是随机过程的结果。因此,尾波的某些性质反映了不均匀介质的平均效应,而与震源到台站的具体路径无关。这个模式成功地解释了这样的观测事实,即不同的微震记录中尾波振幅随时间衰减的形式基本是一致的,与震中距的大小和波传播的具体路径无关。Aki和Chouet(1975)认为,由于散射波所经过的路径比震源距大得多,所以可把台站和震源近似地看作同一个点。在这种情况下,近震图上延迟时间为t的尾波是由半径为β·t/2的球体表面的不均匀体产生的单次反向散射波叠加而成(延迟时间t是从发震时刻算起的,β是S波波速)。如果散射体随空间分布是 相似文献
9.
基于Aki等（1975）的地方震尾波单次散射模型,利用文山地震台记录到2005年8月13日在云南文山县发生的5.3级地震余震序列的数字化波形观测资料,测量了震源区尾波Q（f）值。测量结果表明,当中心频率为1．5Hz时,文山地区的尾波Q值在52～155之间,平均值为91,尾波的振幅衰减率β（f）在0.013～0．039之间,平均值为0．024;测量得到该区尾波Qc值与频率f的关系为Qc（f）=62f^“0.87;尾波波源因子A0与震级ML成正比关系,满足关系lgA0=1．02ML-0．73。此次地震的发震构造为文山断裂带,地震波受到破碎带强烈的非弹性吸收,尾波Qc值明显降低。 相似文献
10.
在月球探测中,星载高频雷达探测仪(HF Radar Sounder)通过月球表面天底点和次表面天底点的回波时延差与强度探测月球分层结构.电磁波在月球分层结构内散射与传播的建模与模拟,对于从雷达探测仪回波中提取微弱的次表面天底点回波,获取次表层结构信息等有重要的意义.本文基于粗糙面散射的Kirchhoff近似与几何光学射线追踪,提出月球分层结构雷达探测回波的模拟方法.根据月球表面地形特征,由规则三角形网格对月表面地形进行数值剖分,数值计算月球表面与次表层面的雷达回波,模拟绕月飞行的星载雷达探测仪对月球表面与次表层结构的探测图像,分析月球表面特征性物理参数对回波的影响.本文所述方法也可以应用到火星等其他外星球次表层结构的探测中. 相似文献
11.
Explorations for the interior structure of the Moon mainly involve three technologies: the early gravitational observations via circumlunar satellites, the moonquake observations during the Apollo period, and the recent high-resolution remote sensing observations. Based on these technologies, we divided the development of the moon’s interior structure into three stages. The first stage is the discovery of high-density anomalous masses (mascons) on the lunar surface with the low-order gravitational field models, which were obtained by observing perturbations of the early lunar orbital satellites. The second stage is the preliminary understanding of the layer structure with the help of moonquake observations during the Apollo period. The third stage is the deep understanding of the structure of the lunar crust, mantle, and core, with the use of high-resolution remote sensing data and the reassessment of moonquake data from the Apollo’s mission. This paper gave detailed introduction and comments on different observation technologies, gathered data, and data processing techniques used at the three stages. In addition, this paper analyzed the current issues in the researches on the Moon’s internal structure and discussed the prospects for future explorations. 相似文献
12.
We present numerical modeling of SH-wave propagation for the recently proposed whole Moon model and try to improve our understanding of lunar seismic wave propagation. We use a hybrid PSM/FDM method on staggered grids to solve the wave equations and implement the calculation on a parallel PC cluster to improve the computing efficiency. Features of global SH-wave propagation are firstly discussed for a 100-km shallow and 900-km deep moonquakes, respectively. Effects of frequency range and lateral variation of crust thickness are then investigated with various models. Our synthetic waveforms are finally compared with observed Apollo data to show the features of wave propagation that were produced by our model and those not reproduced by our models. Our numerical modeling show that the low-velocity upper crust plays significant role in the development of reverberating wave trains. Increasing frequency enhances the strength and duration of the reverberations. Surface multiples dominate wavefields for shallow event. Core–mantle reflections can be clearly identified for deep event at low frequency. The layered whole Moon model and the low-velocity upper crust produce the reverberating wave trains following each phases consistent with observation. However, more realistic Moon model should be considered in order to explain the strong and slow decay scattering between various phases shown on observation data. 相似文献
13.
Estimation of frequency dependent coda wave attenuation structure at the vicinity of Cairo Metropolitan Area 总被引：1，自引：0，他引：1
Salah El-Hadidy M. E. Mohamed Adel Ahmed Deif Ahmed Sayed Abu El-Ata S. R. Moustafa Sayed 《Acta Geophysica》2006,54(2):177-186
Estimation of seismic wave attenuation in the shallow crust in terms of coda wave Q structure previously investigated in the vicinity of Cairo Metropolitan Area was improved using seismograms of local earthquakes
recorded by the Egyptian National Seismic Network. The seismic wave attenuation was measured from the time decay of coda wave
amplitudes on narrow bandpass filtered seismograms based on the single scattering theory. The frequency bands of interest
are from 1.5 to 18 Hz. In general, the values obtained for various events recorded at El-Fayoum and Wadi Hagul stations are
very similar for all frequency bands. A regional attenuation law Q
c
= 85.66 f
0.79 was obtained. 相似文献
14.
本文试用数字地震记录求取尾波Q值及其与频率的关系.在微机上处理触发数字地震仪记录的资料,原始记录经数字滤波器作窄带通滤波得到一组分频记录,经过时间序列分析的方法,可得到能量密度随时间衰减的曲线,该曲线比从可见记录求得的较为可靠.以散射模型的理论表达式进行曲线拟合,求得Q值及其与频率的关系.值得注意的是,这个结果对某一台站并非常数,尾波Q值是时间窗(即研究所用尾波的整个延续时间)的函数,其原因可能是由于不同到时的尾波采样区域和深度不同,以及多次散射的影响等.因此,当把Q值作为地震预报的一个参数时,延续时间是一个重要的可选择的因子. 相似文献
15.
Lunar seismicity and tectonics 总被引：1，自引：0，他引：1
David R. Lammlein 《Physics of the Earth and Planetary Interiors》1977,14(3):224-273
Seismic signals from 300–700 deep moonquakes and about four shallow moonquakes are detected by the long-period seismometers of two or more of the Apollo seismic stations annually. Deep-moonquake activity detected by the Apollo seismic network displays tidal periodicities of 0.5 and 1 month, 206 d and 6 a. Repetitive moonquakes from 60 hypocenters produce seismograms characteristic of each. At each hypocenter, moonquakes occur only within an active period of a few days during a characteristic phase of the monthly lunar tidal cycle. An episode of activity may contain up to four quakes from one hypocenter. Nearly equal numbers of hypocenters are active at opposite phases of the monthly cycle, accounting for the 0.5-month periodicity. The 0.5- and 1-month activity peaks occur near times of extreme latitudinal and longitudinal librations and earth-moon separation (EMS). The 206-d and 6-a periodicities in moonquake occurrence and energy release characteristics are associated with the phase variations between the librations and EMS. Because of the exact relationship between tidal phases and the occurrence of deep moonquakes from a particular hypocenter, it is possible to predict not only the occurrence times from month to month, often to within several hours, but also the magnitudes of the moonquakes from that hypocenter. The predicted occurrence of large A1 moonquakes in 1975, following a 3-a hiatus, confirms the correlation between A1-moonquake activity and the 6-a lunar tidal cycle and implies a similar resurgence for all of the deep moonquakes. Because no matching shallow moonquake signals have been identified to date, tidal periodicities cannot be identified for the individual sources. However, shallow moonquakes generally occur near the times of extreme librations and EMS and often near the same tidal phase as the closest deep moonquake epicenters. With several possible exceptations, the deep-moonquake foci located to date occur in three narrow belts on the nearside of the moon. The belts are 100–300 km wide, 1,000–2,500 km long and 800–1,000 km deep and define a global fracture system that intersects in central Oceanus Procellarum. A fourth active, although poorly defined, zone is indicated. The locations of 17 shallow-moonquake foci, although not as accurate as the deep foci, show fair agreement with the deep-moonquake belts. Focal depths calculated for the shallow moonquakes range from 0–200 km. Deep-moonquake magnitudes range from 0.5 to 1.3 on the Richter scale with a total energy release estimated to be about 1011 erg annually. The largest shallow moonquakes have magnitudes of 4–5 and release about 1015–1018 erg each. Tidal deformation of a rigid lunar lithosphere overlying a reduced-rigidity asthenosphere leads to stress and strain concentrations near the base of the lithosphere at the level of the deep moonquakes. Although tidal strain energy can account for the deep moonquakes in this model, it cannot account for the shallow moonquakes. The tidal stresses within the lunar lithosphere range from about 0.1 to 1 bar and are insufficient to generate moonquakes in unfractured rock, suggesting that lunar tides act as a triggering mechanism. The largest deep moonquakes of each belt usually occur near the same characteristic tidal phases corresponding to near minimum or maximum tidal stress, increasing tidal stress, and alignments of tidal shear stresses that correspond to thrust faulting along planes parallel to the moonquake belts and dipping 30–40°. With few exceptions, the shallow moonquakes occur at times of near minimum tidal stress conditions and increasing tidal stress that also suggest thrust faulting. The secular accumulation of strain energy required for the shallow moonquakes and implied by the uniform polarities of the deep moonquake signals probably results from weak convection. A convective mechanism would explain the close association between moonquake locations and the distribution of filled mare basins and thin lunar crust, the earth-side topographic bulge, and the ancient lunar magnetic field. The low level of lunar seismic activity and the occurrence of thrust faulting both at shallow and great depths implies that the moon is presently cooling and contracting at a slow rate. 相似文献
16.
Arthur Frankel 《Pure and Applied Geophysics》1989,131(4):639-685
This paper reviews applications of the finite-difference and finite-element methods to the study of seismic wave scattering in both simple and complex velocity models. These numerical simulations have improved our understanding of seismic scattering in portions of the earth where there is significant lateral heterogeneity, such as the crust. The methods propagate complete seismic wavefields through highly complex media and include multiply scattered waves and converted phases (e.g.,P toSV, SV toP, body wave to surface wave). The numerical methods have been especially useful in cases of moderate and strong scattering in complex media where multiple scattering becomes important. Progress has been made with numerical methods in understanding how near-surface, low-velocity basin structures scatter surface waves and vertically-incident body waves. The numerical methods have proven useful in evaluating scattering of surface waves and body waves from topography of both the free surface and interfaces buried at depth. Numerical studies have demonstrated the importance of conversions from body waves to surface waves (andvice versa) when lateral heterogeneities and topographic relief are present in the uppermost crust. Recently, several investigations have applied numerical methods to study seismic wave propagation in velocity models which vary randomly in space. This stochastic approach seeks to understand the effects of small-scale complexity in the earth which cannot be resolved deterministically. These experiments have quantified the relationships between the statistical properties of the random heterogeneity and the measurable properties of high-frequency (1 Hz) seismograms. These simulations have been applied to the study of many features observed in actual high-frequency seismic waves, including: the amplitude and time decay of seismic coda, the apparent attenuation from scattering, the dispersion of waveforms, and the travel time and waveform variations across arrays of receivers. 相似文献
17.
The lunar crust at the Apollo 16 landing site contains substantial amounts of a “primitive component” in which the ferromagnesian group of elements is concentrated. The composition of this component can be retrieved via an analysis of mixing relationships displayed by lunar breccias. It is found to be a komatiite which is compositionally similar to terrestrial komatiites both in major and minor elements. The komatiite component of the lunar crust is believed to have formed by extensive degrees of melting of the lunar interior at depths greater than were involved in the formation of the lunar magma ocean which was parental to the crust. After formation of the anorthositic crust, it was invaded by extensive flows and intrusions of komatiite magma from these deeper source regions. The komatiites became intimately mixed with the anorthosite by intensive meteoroid impacts about 4.5 b.y. ago, thereby accounting for the observed mixing relationships displayed by the crust. The compositional similarity between lunar and terrestrial komatiites strongly implies a corresponding similarity between the compositions of their source regions in the lunar interior and the Earth's upper mantle. The composition of the lunar interior can be modelled more specifically by combining the komatiite composition with its liquidus olivine composition (as determined experimentally) in proportions chosen so as to produce a cosmochemically acceptable range of Mg/Si ratios for the bulk Moon. Except for higher FeO and lower Na2O, the range of compositions thereby obtained for the bulk moon is very similar to the composition of the Earth's upper mantle.The effects of meteoritic contamination on the abundances of cobalt and nickel in lunar highland breccias were subtracted on the assumption that the contaminating projectiles were chondritic. The cobalt and nickel residuals thereby obtained were found to correlate strongly with the (Mg + Fe) content of the breccias, demonstrating that the Co and Ni are associated with the ferromagnesian component of the breccias and are genuinely indigenous to the Moon. The lunar highland Co and Ni residuals also display striking Ni/Co versus Ni correlations which follow a similar trend to those displayed by terrestrial basalts, picrites and komatiites. The lunar trends provide further decisive evidence of the indigenous nature of the Co and Ni residuals and suggest the operation of extensive fractionation controlled by olivine-liquid equilibria in producing the primitive component of the lunar breccias. Indigenous nickel abundances at the Apollo 14, 15 and 17 sites are much lower than at the Apollo 16 site, although rocks from all sites follow the same Ni/Co versus Ni trends. It is suggested that the primitive component at the Apollo 14, 15 and 17 sites was generally of basaltic composition, in contrast to the komatiitic nature of the Apollo 16 primitive component. 相似文献
18.
The phenomenon of the seismic coda, which is composed of seismic energy delayed by scattering, is seen on both the Earth and the Moon. On the Moon the scattered coda is very large relative to body wave arrivals with a delay of the time of maximum energy, whereas on Earth scattered codas are relatively small and show no delay of the energy maximum. In both cases the form of the coda is controlled by three distance scales, the mean free path L, which is the average distance seismic energy travels before it is scattered, the attenuation distance , which is the average distance seismic energy travels before it is attenuated, and the source-receiver distance R. Two coda models are discussed based on these parameters; a strong scattering (diffusion) model, and a weak scattering (single scattering) model. A discussion of the diffusion scattering model indicates that if , diffusion scattering is an appropriate model, but if , single scattering is the appropriate model, within the appropriate range of R. A survey of the literature indicates that for the frequency range 0.5–10 Hz, diffusion scattering is important in lunar codas, but for the frequency range 1–25 Hz single scattering is important in terrestrial codas. Another important effect of attenuation is the elimination of scattering paths much longer than . On the Moon, this means that seismic energy in the coda can only propagate directly in the near-surface strong scattering zone between surface sources and the seismometer for source-seismometer separations of the order of ; otherwise, scattering is limited to regions near the source and the receiver. On Earth, this effect probably prevents multiple scattering. 相似文献
19.
根据中朝地台东北缘地区 (东经 1 1 7°0 0′— 1 2 6°0 0′ ,北纬 36°0 0′— 44°0 0′) 1 980— 1 997年的 380 0 0余条P波走时数据 ,利用正交投影法重建了该区地壳和上地幔的三维速度结构 .通过分析及同人工地震测深剖面的详细对比 ,证明了成像结果的可靠性 .结果表明 :中朝地台东北缘地区地壳上地幔介质存在显著的横向不均匀性 ,直至 1 2 0km深度处依然明显 ;地壳上部的速度图像清楚地反映了不同岩石单元的分布与该区不同性质的基岩分布基本吻合 ;从上、中地壳的速度图像中发现了研究区存在海城、朝阳、义县、丹东南、唐山等几个低速异常区(即速度逆反层区 ) ,其中海城、唐山、朝阳等地区的壳内低速层已由深地震测深资料所证实 ;研究区陆地发生的几次强震均发生于壳内低速层上方的高速脆性介质内 ,而渤海发生的强震 ,此现象不明显 ,但都发生于横向介质速度显著突变的位置 ;在地壳不同深度上发现了普兰店至山海关横跨渤海的北西向低速异常带 ;地震层析二维速度图像与深地震测深资料的对比表明 ,研究区利用地震层析成像技术 ,在一定条件下可以获得与人工地震测深相似的效果 相似文献
20.
Passive seismic techniques have revolutionarised seismology,leading for example to increased resolution in surface wave tomography,to the possibility to monitor changes in the propagation medium,and to many new processing strategies in seismic exploration.Here we review applications of the new techniques to a very particular dataset,namely data from the Apollo 17 lunar network.The special conditions of the lunar noise environment are investigated,illustrating the interplay between the properties of the noise and the ability to reconstruct Green's functions.With a dispersion analysis of reconstructed Rayleigh waves new information about the shallow shear velocity structure of the Moon are obtained.Passive image interferometry is used to study the effect of temperature changes in the subsurface on the seismic velocities providing direct observation of a dynamic process in the lunar environment.These applications highlight the potential of passive techniques for terrestrial and planetary seismology. 相似文献