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1.
Cheng Yinhe Zhou Shengqi Wang Dongxiao Lu Yuanzheng Huang Ke Yao Jinglong You Xiaobao 《中国海洋湖沼学报》2016,34(3):619-628
The observed characteristics of lower atmospheric ducts over the South China Sea(SCS) were analyzed based on Global Position Systerm(GPS) radiosonde data collected four times daily during autumn open cruises from 2006 to 2012.Duct occurrence,thickness,and strength over the SCS were about 40%,150-m thick,and 8 M units,respectively,which were larger than during the summer monsoon period.Most ducts occurred at heights 1 500 m and these ducts easily trap electromagnetic wave clusters with wavelengths 2 m.Diurnal variation of the SCS ducts appeared evident.They occurred more often at midnight at higher altitudes(about 1 100 m),with a thickest layer of about 145 m and less frequently during the evening at lower altitudes(about 800 m),with a thinnest layer of about 125 m.Moreover,ducts during the daytime at a mean height of about 900 m,with the greatest strength of about 10 M units.Furthermore,all duct variables observed over the SCS in autumn decreased from north to south.These findings are useful not only in the design of radar and communication systems,but also for evaluating possible effects of anomalous propagation on meteorological radar and military applications. 相似文献
2.
目前人类对地球的认识仍很肤浅,无论国外还是国内对于地球动力学问题仍在探索过程中,Science杂志2005年公布的125个重大科学问题中的第10个问题是“地球内部是如何运行的”,提出地球动力来源还尚未解决。 2017年出版的《中国学科发展战略--板块构造与大陆动力学》认为板块构造理论虽然取得了巨大成功,但该学说依然存在其形成以来就存在的难题,即板块动力、板块起源及板块上陆三大问题,驱动板块运动的动力机制是最为重要的问题,也是亟待解决的问题。
研讨会分两个环节,一是主要观点报告环节,二是讨论争鸣环节。
在报告环节,涉及动力机制的主要有5位报告人,分别阐述了他们的主要观点。梁光河提出了新大陆漂移说,通过大量证据分析认为传统的海底扩张驱动大陆漂移的模式存在很多问题,很多地质和地球物理观测事实说明持续推动大陆漂移的动力不是海底的持续扩张,而是大陆板块后下方持续的岩浆上涌推动大陆板块向前漂移,那是一个自发的连锁反应。万天丰认为传统的海底扩张传送带模式很难解释大陆板块漂移速度远远大于地幔对流速度这个问题,提出了陨击说。陨石撞击诱发地幔底劈推动大陆板块运动这个新的驱动模式。唐春安提出了地球龟裂说,认为地球内部热能的积累与释放,使得地质历史上岩石圈地幔具有冷热交替的周期。毛小平分析认为,目前所提出的地球动力中,只有周向应力具有足够数量级的应力,可以推动板块运动;周向应力在岩石圈薄弱处释放从而产生地壳相对运动;长期以来解释不了的“地壳异常压力”其实就是周向应力,而可独立于重力的构造力、碰撞力并不存在。
在讨论争鸣环节,大家针对地壳运动的动力来源自由发言。梁光河指出万天丰提出的陨石撞击可以较好地解释超大陆裂解的初始动力,但不同意陨石撞击可以提供持续的大陆漂移的动力,以印度板块的北漂为例,因为地幔的巨大黏滞阻力,需要无数个陨石定点撞击印度板块后面才可能持续推动印度板块漂移。唐春安提出地球的锅盖效应,因此上地幔具有冷热周期,在热周期地壳才会大规模漂移,按照力学机制,大洋中脊和转换断层不可能是海底扩张产生的,应该是大陆漂移拉开产生的断裂系统。最后杨巍然总结发言,认为陨石撞击是一个重要因素,地球上的构造运动都可以归结为开合运动,海底扩张和大陆漂移都是存在的,地体构造也是科学的。研讨会取得的共识是：大陆的确存在大规模水平运动,传统的地幔对流传送带驱动模式存在很多与观测事实不符的问题,需要重新认识驱动机制和驱动力的问题,对板块俯冲问题多数持怀疑甚至反对的观点。其驱动力应该来自重力和地球内部热力,但它们之间是如何相互作用的,仍需要进行更深入的研究。 相似文献
3.
Jianghai Xia Richard D Millerg Xu Yixian Luo Yinhe Chen Chao Liu Jiangping Julian Ivanov Chong Zeng 《中国地质大学学报(英文版)》2009,20(3)
High-frequency (≥2 Hz) Rayleigh-wave data acquired with a multichannei recording sys-tem have been utilized to determine shear (S)-wave velocities in near-surface geophysics since the early 1980s. This overview article discusses the main research results of high-frequency surface-wave tech-niques achieved by research groups at the Kansas Geological Survey and China University of Geosciences in the last 15 years. The multichannel analysis of surface wave (MASW) method is a nou-iuvasive acoustic approach to estimate near-surface S-wave velocity. The differences between MASW results and direct borehole measurements are approximately 15% or less and random. Studies show that simultaneous inversion with higher modes and the fundamental mode can increase model resolution and an investigation depth. The other important seismic property, quality factor (Q), can also be estimated with the MASW method by inverting attenuation coefficients of Rayleigh waves. An inverted model (S-wave velocity or Q) obtained using a damped least-squares method can be assessed by an optimal damping vector in a vicinity of the inverted model determined by an objective function, which is the trace of a weighted sum of model-resolution and model-covariance matrices. Current developments include modeling high-frequency Rayleigh-waves in near-surface media, which builds a foundation for shallow seismic or Rayleigh-wave inversion in the time-offset domain; imaging dispersive energy with high resolution in the frequency-velocity domain and possibly with data in an arbitrary acquisition geometry, which opens a door for 3D surface-wave techniques; and successfully separating surface-wave modes, which provides a valuable tool to perform S-wave velocity profiling with high-horizontal resolution. 相似文献
4.
Pseudospectral modeling and dispersion analysis of Rayleigh waves in viscoelastic media 总被引：1，自引：0，他引：1
Multichannel Analysis of Surface Waves (MASW) is one of the most widely used techniques in environmental and engineering geophysics to determine shear-wave velocities and dynamic properties, which is based on the elastic layered system theory. Wave propagation in the Earth, however, has been recognized as viscoelastic and the propagation of Rayleigh waves presents substantial differences in viscoelastic media as compared with elastic media. Therefore, it is necessary to carry out numerical simulation and dispersion analysis of Rayleigh waves in viscoelastic media to better understand Rayleigh-wave behaviors in the real world. We apply a pseudospectral method to the calculation of the spatial derivatives using a Chebyshev difference operator in the vertical direction and a Fourier difference operator in the horizontal direction based on the velocity–stress elastodynamic equations and relations of linear viscoelastic solids. This approach stretches the spatial discrete grid to have a minimum grid size near the free surface so that high accuracy and resolution are achieved at the free surface, which allows an effective incorporation of the free surface boundary conditions since the Chebyshev method is nonperiodic. We first use an elastic homogeneous half-space model to demonstrate the accuracy of the pseudospectral method comparing with the analytical solution, and verify the correctness of the numerical modeling results for a viscoelastic half-space comparing the phase velocities of Rayleigh wave between the theoretical values and the dispersive image generated by high-resolution linear Radon transform. We then simulate three types of two-layer models to analyze dispersive-energy characteristics for near-surface applications. Results demonstrate that the phase velocity of Rayleigh waves in viscoelastic media is relatively higher than in elastic media and the fundamental mode increases by 10–16% when the frequency is above 10 Hz due to the velocity dispersion of P and S waves. 相似文献
5.
Yinhe Luo Jianghai Xia Yixian Xu Chong Zeng Richard D. Miller Qingsheng Liu 《Pure and Applied Geophysics》2009,166(3):353-374
Multichannel analysis of surface waves (MASW) method is a non-invasive geophysical technique that uses the dispersive characteristic
of Rayleigh waves to estimate a vertical shear (S)-wave velocity profile. A pseudo-2D S-wave velocity section is constructed
by aligning 1D S-wave velocity profiles at the midpoint of each receiver spread that are contoured using a spatial interpolation
scheme. The horizontal resolution of the section is therefore most influenced by the receiver spread length and the source
interval. Based on the assumption that a dipping-layer model can be regarded as stepped flat layers, high-resolution linear
Radon transform (LRT) has been proposed to image Rayleigh-wave dispersive energy and separate modes of Rayleigh waves from
a multichannel record. With the mode-separation technique, therefore, a dispersion curve that possesses satisfactory accuracy
can be calculated using a pair of consecutive traces within a mode-separated shot gather. In this study, using synthetic models
containing a dipping layer with a slope of 5, 10, 15, 20, or 30 degrees and a real-world example, we assess the ability of
using high-resolution LRT to image and separate fundamental-mode Rayleigh waves from raw surface-wave data and accuracy of
dispersion curves generated by a pair of consecutive traces within a mode-separated shot gather. Results of synthetic and
real-world examples demonstrate that a dipping interface with a slope smaller than 15 degrees can be successfully mapped by
separated fundamental waves using high-resolution LRT. 相似文献
6.
本文基于2007—2018年Landsat系列遥感卫星数据开展田湾核电站温排水时空变化特征及其影响分析。采用辐射传输方程算法和劈窗算法对核电站周围海域的海表温度进行反演,通过星星匹配对反演温度的精度进行验证。匹配验证结果表明,反演的Landsat海表温度与MODIS海表温度产品具有较好的一致性,决定系数达到0.91。基于研究海域温度反演结果分析了核电站温排水面积的季节变化、年际变化和潮周期内变化特征,并且分析了潮汐与风场对温排水扩散的影响。结果表明,核电站周边海域各季节的温升区面积存在明显差异,春季最大,可达秋季的7倍;2007—2018年,随着装机容量的扩大,温排水面积不断扩大,2018年达到峰值,瞬时最大面积可达101.7 km2;潮汐对温排水扩散有影响,涨憩时刻温升区面积较落憩时刻大;有利风会促进温排水扩散,但影响有限。 相似文献
7.
基于探空数据的南海表面波导统计特征研究 总被引：1，自引：0，他引：1
Based on the global position system(GPS) radiosonde data near the sea surface, the surface duct characteristics over the South China Sea(SCS) were statistically analyzed. The annual surface duct occurrence over the SCS was about 64%. Of the observed surface ducts, duct heights mainly distributed between 18 and 42 m, with M slopes in the range of –0.3 to –0.2 M units/m. Those ducts accounted for about 80% of the ducting cases. For the total profiles, the duct occurrences in a day changed slowly and were more than 60% in all times. The surface ducts formed more easily in the daytime than in the nighttime and most of the duct height were at bellow about 32 m.Additionally, The seasonal variation of the SCS ducts appeared to be evident, except that the mean duct thickness was almost constant, about 33 m for all seasons. The highest occurrence was about 71% in the autumn, followed by in the summer, spring and winter. In spring, their top-height existed more often at a height of more than 48 m.Their mean duct strength became stronger trend from spring to winter, with the M-slope in the range between–0.26 and –0.18 M units/m. Those results agreed well with other studies, provided considering the data resolution.The statistical analysis was reliable and gave the duct estimation for the SCS. Such duct climatology not only has important implications for communication systems and the reliability of the radar observation, but also can provide useful information to improve the accuracy of the meteorological radar measurements. 相似文献
8.
Advantages of Using Multichannel Analysis of Love Waves (MALW) to Estimate Near-Surface Shear-Wave Velocity 总被引：2，自引：1，他引：1
Jianghai Xia Yixian Xu Yinhe Luo Richard D. Miller Recep Cakir Chong Zeng 《Surveys in Geophysics》2012,33(5):841-860
As theory dictates, for a series of horizontal layers, a pure, plane, horizontally polarized shear (SH) wave refracts and reflects only SH waves and does not undergo wave-type conversion as do incident P or Sv waves. This is one reason the shallow SH-wave refraction method is popular. SH-wave refraction method usually works well defining near-surface shear-wave velocities. Only first arrival information is used in the SH-wave refraction method. Most SH-wave data contain a strong component of Love-wave energy. Love waves are surface waves that are formed from the constructive interference of multiple reflections of SH waves in the shallow subsurface. Unlike Rayleigh waves, the dispersive nature of Love waves is independent of P-wave velocity. Love-wave phase velocities of a layered earth model are a function of frequency and three groups of earth properties: SH-wave velocity, density, and thickness of layers. In theory, a fewer parameters make the inversion of Love waves more stable and reduce the degree of nonuniqueness. Approximating SH-wave velocity using Love-wave inversion for near-surface applications may become more appealing than Rayleigh-wave inversion because it possesses the following three advantages. (1) Numerical modeling results suggest the independence of P-wave velocity makes Love-wave dispersion curves simpler than Rayleigh waves. A complication of “Mode kissing” is an undesired and frequently occurring phenomenon in Rayleigh-wave analysis that causes mode misidentification. This phenomenon is less common in dispersion images of Love-wave energy. (2) Real-world examples demonstrated that dispersion images of Love-wave energy have a higher signal-to-noise ratio and more focus than those generated from Rayleigh waves. This advantage is related to the long geophone spreads commonly used for SH-wave refraction surveys, images of Love-wave energy from longer offsets are much cleaner and sharper than for closer offsets, which makes picking phase velocities of Love waves easier and more accurate. (3) Real-world examples demonstrated that inversion of Love-wave dispersion curves is less dependent on initial models and more stable than Rayleigh waves. This is due to Love-wave’s independence of P-wave velocity, which results in fewer unknowns in the MALW method compared to inversion methods of Rayleigh waves. This characteristic not only makes Love-wave dispersion curves simpler but also reduces the degree of nonuniqueness leading to more stable inversion of Love-wave dispersion curves. 相似文献
9.
Mantle Transition Zone Structure Beneath Southeastern China and its Implications for Stagnant Slab and Water Transportation in the Mantle 总被引：3，自引：0，他引：3
We determined depth variation of the 410- and 660-km discontinuities beneath southeastern China by common-converted-point stacking of \(\rm P\) -wave receiver functions of 121 permanent Chinese seismic stations. We then combined the results with seismic velocity variation to estimate temperature and water content variations in the mantle transition zone of the region. Previous tomographic studies have shown a stagnant slab in the mantle transition zone in eastern Asia that is connected to subduction of the western Pacific. Temperature variations obtained clearly outline the shape of the stagnant slab, with its western edge at 113.5 \(^\circ\) E and the southern edge at 28.5 \(^\circ\) N. The correlation between the location of the stagnant slab and surface tectonics suggests that the Cenozoic extension in eastern China is closely associated with the subduction of the western Pacific and its eastward migration. The water content of the stagnant slab is lower than in surrounding slabs, suggesting that the water has already been released from the subducting slab into the upper mantle. 相似文献
10.
石油地震资料揭示塔里木盆地中央巴楚隆起为结晶基底和古生代地层相对隆升区,地表为第四纪陆相碎屑岩不整合覆盖,隐伏隆起大部分区域缺失中、新生界。在隆起南北两侧构造变形比较强烈,均发育基底卷入的逆冲构造和古生界内逆冲构造。根据钻井资料和二维地震测线详细的构造解释,应用断层相关褶皱理论得知：吐木休克基底卷入逆冲断层是在中生界早期形成的基底卷入楔形构造的基础上,在新生界晚期再次活动形成的;新生代晚期中亚地区强烈陆内变形,导致塔里木盆地先期形成的巴楚隆起再次挤压隆升;晚期变形过程中,先存构造与形成新构造挤压方向的偏差导致新构造发育有走滑分量,形成典型的斜向挤压构造——吐木休克旋转弧形构造。平面分布上,弧形构造东西向延伸的中段和北东向延伸的西段,早期为基底卷入楔形构造,晚期发育基底卷入逆冲构造;近北西向延伸的东段,晚期发育基底卷入楔形构造叠加在早期基底卷入楔形构造之上,说明该构造至少经历了两期变形。由于晚期基底卷入逆冲断层具有走滑分量,导致盖层单斜构造发育3类应变带及相应构造：拉伸变形带发育的正断层、剪切变形带发育的走滑断层及挤压应变带即走滑构造分量;西段发育左行逆冲走滑断裂带及伸展变形;东段发育右行逆冲走滑断裂带。弧形构造西部发育的构造样式与2012年Keating等模拟的斜向断层位移形成的构造样式非常相似,说明弧形构造西段吐木休克基底卷入逆冲构造具有走滑分量,从而合理地解释了该区发育的构造样式及正断层形成机制。 相似文献