利用背景噪声进行地震成像的新方法

利用背景地震噪声提取格林函数，即通过一对台站记录的地震噪声进行互相关计算，来近似台站间的格林函数，并进一步通过地震成像获取地下结构的认识，成为最近跨学科研究的热点问题之一.本文首先叙述了其发展背景及过程，然后分别从四个角度，简要介绍了目前对其物理原理的解释.如果该方法能得到进一步的发展，将不再依赖于天然地震以及人工地震，而仅仅利用地震台站记录的地震噪声便可获取高分辨率的地下成像.该方法将会大大促进地震学的发展.     

利用地震光照成像法研究青藏高原东南缘岩石圈间断面结构及其动力学意义

为了进一步认识青藏高原东南缘的构造演化等动力学问题以及该区域的深部孕震机理,本文使用位于该区域内的中国地震科学台阵探测项目的台站所记录到的远震P波波形数据,采用地震光照成像法获取了岩石圈间断面的结构,并讨论了该方法的准确性和稳定性。研究结果显示,青藏高原东南缘的岩石圈西薄东厚,其中:滇缅泰地块腾冲火山附近最薄,约为60 km,其较薄的岩石圈可能是软流圈地幔物质上涌造成的;扬子地块岩石圈厚度从四川盆地向南逐渐减薄,特别是四川盆地下方最厚,可达190 km左右;滇缅泰地块腾冲火山下方150 km深度左右探测到明显的间断面,该间断面可能是腾冲火山原始岩浆源的位置即岩浆源。本研究所得结果 “印支地块与滇缅泰地块结构的连续性” 进一步为印度板块的推挤作用造成腾冲火山低速物质向东溢出的结论提供了地震学证据。此外,研究区域最北端的剖面显示,峨眉山大火成岩省的内带在50—250 km深度范围及其上方地壳内存在明显的局部高速异常,其不均匀分布特征可能与二叠纪火山喷发过程中岩浆底侵及中新生代以来多期次构造活动有关。      

A review of the wave gradiometry method for seismic imaging

As dense seismic arrays at different scales are deployed, the techniques to make full use of array data with low computing cost become increasingly needed. The wave gradiometry method(WGM) is a new branch in seismic tomography, which utilizes the spatial gradients of the wavefield to determine the phase velocity, wave propagation direction, geometrical spreading, and radiation pattern. Seismic wave propagation parameters obtained using the WGM can be further applied to invert 3D velocity models,...     

一种新的地震危险性表达方法研究

为了寻找一种精度较高、超越概率范围较广并且便于应用的方式来表达地震危险性,本文回顾了当前常用的几种地震危险性表达方法,提出基于一个新函数来拟合地震危险性曲线的“特征系数法”,并使用《中国地震动参数区划图》（GB 18306—2015）的基础数据对该函数的拟合效果进行了验证。结果表明,新函数与地震危险性曲线拟合良好,与极值函数相比有明显的提升,能够充分地表达一个场点的地震危险性。另外,本文结果还显示该函数中表征曲线形状的参数k （文中称为特征系数）与场点面临的地震环境有关,k值较低的场点危险性贡献基本来自近场,而k值较高的场点中远距离的贡献是不能忽视的。      

一种新地震定位方法研究

提高地震定位精度一直是地震学应用研究的重要课题之一,目前已经发展了多种方法用于台网定位。这些方法的共同弱点是应对复杂情况的能力差、震后处理时间过长、不能根据地震信息的增加自动修改速度模型而提高下一次地震定位的精度。开发地震台网资源,使之实现地震预警的功能,必须解决地震快速定位问题。为此,本文提出了一种基于地震台网资料的网格化地震定位方法。震前建立每个区间网格到台站的理论走时数据库,震时仅通过优化搜索,以每两个台站的到时差与理论走时差之间的方差最小的网格位置为震源,并得到发震时刻。通过在黑龙江省地震台网的实际应用说明方法可靠,精度较高。     

Station corrections for the Kaapvaal seismic network: Statistical properties and relation to lithospheric structure

Station corrections for body wave travel times are required to compensate for lateral variations in the crust and uppermost mantle in the analysis of seismic travel times that are used to determine deep Earth structure by various methods, including tomography. Station corrections to be applied to P wave arrival times from teleseismic earthquakes recorded by the Kaapvaal seismic network were estimated by five different methods: (1) averaging, (2) computing the median, and (3) weighted averaging of residuals; (4) least-squares regression, and (5) weighted least-squares regression. The corrections display variations that are related to the tectonic features of southern Africa inferred from surface geology, clearly delineating the southern and central areas of both the Kaapvaal and Zimbabwe cratons as regions of early arrivals, and the area around the Bushveld complex by later arrivals. Use of a simple ray method for generating synthetic station corrections suggests that lateral variations in the top 230 km of the Earth can explain the observed pattern of variations in station corrections. A satisfactory way of compensating for the biasing effects of outliers in the individual estimates of station corrections is through adaptation of a method originally developed by Jeffreys, which involves ascribing weights to the observations that reduce the standard deviation on a single estimate of a station correction from 0.123 to 0.096 s. Methods (2), (3) and (5) avoid serious bias by outliers, although methods (3) and (5) are preferred, because they also provide information on the causes of outliers. The presence of some outliers cannot be explained by errors in the measurement process, but must be caused by timing errors at the stations during recording, and/or errors introduced during the process of constructing the archived data files from the field data.     

On the 650-km seismic discontinuity

The pressure-temperature conditions and the variations of both density and bulk sound velocity in the vicinity of the 650-km discontinuity have been compared with those calculated for the phase transitions in both the olivine and the pyroxene-garnet components of the mantle material. These studies suggest that the mantle below about 650 km is composed primarily of perovskite phase, as distinct from the olivine-rich upper mantle. Thus, the “650-km” discontinuity is not likely to be associated with any of the equilibrium phase boundaries observed in olivine, pyroxene, and garnet, and is proposed instead to be a chemical change. It is suggested that the following factors may be responsible for chemical separation: the pyroxene-garnet component transforms to much denser phases possessing the ilmenite and perovskite structures before the breakdown of the spinel phase into a mixture of perovskite plus rocksalt phases. The perovskite phase is also much denser than the rocksalt phase and the two phases may not form a gravitationally stable mixture. Thus, the denser phases may tend to sink to or stay at the deep part of the mantle, causing chemical separation. Possible separation processes are discussed and the supporting observations are presented.     

华北大地电磁测深阵列观测实验与岩石圈导电性快速成像模型

关于中国大陆岩石圈导电性结构研究越来越引起人们的重视,而目前研究大陆岩石圈导电性结构的主要方法是大地电磁测深（Magnetotelluric sounding）.为此,在国家项目"深部探测技术与实验研究（SinoProbe）"专项里开展了"大陆电磁参数标准网实验（SinoProbe-01）"研究,完成了华北1°×1°地理坐标网度的大地电磁测深"标准点"阵列（Array）观测.本文详细论述了华北SinoProbe-01项目1°×1°MT"标准点"阵列观测实验的概况,以及通过精细的MT数据处理和一维Niblett-Bostick变换快速成像,所获取的华北地区岩石圈导电性三维成像模型.在分析华北岩石圈导电性结构特征的基础上,从电性结构角度把华北与邻区岩石圈划分为胶辽、燕山、鲁西、太行—吕梁等低导电性（高电阻率）块体,内蒙古、阿拉善和祁连中等导电性块体和黄淮、鄂尔多斯、秦岭良导电性（低电阻率）块体,进一步从导电性的角度证实了华北克拉通是由多个块体集合而成的观点.     

A new method for determining weathering rates in weathering pits

Determining the rates of rock weathering is difficult because, firstly, the weathering rate of rocks is usually so slow that it is difficult to measure; secondly, it is also difficult to determine the start time and duration of weathering. The Shanxi River Valley in Fujian, China dried up after a reservoir was built upstream in 1959, and became a stone quarry site. Quarrying ceased in 1977, so a large amount of quarry wastes with artificially excavated surfaces were left in the valley. The concave-upward curved rocky surface, broken by manual excavation, easily contains rainwater in its central part, which was easily weathered into a more concave surface. Plaster mould casting was performed in situ on such a concave surface of an excavated stone rock in the valley and scanned with a high-precision 3D scanner to obtain 3D data of the concave-upward rock surface and its more concave middle part, which was considered as an initial weathering pit. The 3D model provided an in-depth understanding of the initial formation process of weathering pits, indicating that: (1) the average weathering rate of a weathering pit is 10.8 ± 0.49 cm ka⁻¹; (2) weathering pits are generally formed by standing water in depressions on a flat near-horizontal rock surface due to weathering actions involving water; (3) the deepening rate of a weathering pit is about four times greater than that of the surrounding area; (4) the growth of a weathering pit can begin in some small concavities on the flat rock surface without pre-existing depressions and gradually expands; (5) a weathering pit is generally wider than deep or with a flat bottom due to expansion with a lateral weathering rate that is greater than that of the vertical, and the lamination of the host rock is not necessary for the formation of flat-floored weathering pits. © 2020 John Wiley & Sons, Ltd.     

A lithospheric seismic profile along the axis of the Alps, 1975

Summary From 8 to 20 September 1975 refraction seismic measurements were carried out in close European cooperation on a long range profile along the strike of the Alps between France and Hungary. The execution and first results of the Alpine Longitudinal Profile 1975 are presented in this paper, which is the first of a series. 20 shots from 9 different shotpoints were recorded by 193 mobile stations along a main line of a length of 850 km as well as on a number of fans and additional shorter profiles. The recordings were subsequently digitized and a number of computer generated record sections are presented to illustrate the quality of the data. First results are given in the form of a simple crustal cross section along the main profile and of two velocity depth functions, which indicate a substantial difference in type between the westernmost part and the eastern part of the profile.G. Angenheister, J. Ansorge, K. Aric, D. Bamford, R. Cassinis, H. Gebrande, I. Guerra, R. Gutdeutsch, W. Kaminski, R. King, H. Miller, C. Morelli, St. Mueller, R. Nicolich, G. perrier, K. Posgay, C. Prodehl, S. Scarascia, E. Schmedes, P. Steinhauser, F. Thouvenot.     

Implication of seismic noise for determining the structure of the upper Earth Rock Mass

An assertion that the cross-correlation function of seismic noise, considered as a result of the superposition of the surface waves, excited by the sources, randomly distributed over the Earth’s surface, determines the Green function of the surface wave is verified by numerical modeling. The maximum wave periods, for which this assertion is correct, are estimated and the errors in determination of the phase and group velocity of the surface waves are evaluated. The procedure for the determination of the correlation function and estimation from it of the group velocity are tested thoroughly based on the example of the pair of the BJT and TLY stations in Asia. This procedure is used for obtaining the group and phase velocities of the Rayleigh waves on the traces between the OBN-ARU and PUL-ARU stations. The velocity sections of the transverse waves are built based on the dispersion curves of the phase and group velocities of averages along these traces. The region of the lowered velocity in the upper mantle at depths of 150–300 km is revealed on both traces. From the analysis of correlation functions, which are subjected to narrow-band filtering, it is shown that the frequency composition of noise varies from the East and from the West from the profiles between the stations: in the East (Siberia) the noise has an appreciably lower-frequency than in the West (Western Europe).     

A new method of migration imaging for MT data

Introduction The migrationof electromagnetic field is like that of elastic wave in seismic prospecting, butthere are some differences between them (Lee et al, 1989). The elastic wave field satisfies thegeneral wave equation, while the electromagnetic field in our study satisfies the diffusion equation.Both the electromagnetic field and the elastic wave field have a similar mechanism. The imagingfunction named map can characterize the interface of different mediums (MA, 1989), that is …     

地震映像数据的时频分析方法及应用

本文研究地震映像数据的时频解释方法.采用短时傅立叶变换方法获得地震映像记录频谱的时间与空间分布,根据介质对地震波频谱影响的基本规律,通过分析已知地质断面地震映像记录频谱的时间与空间分布,研究了综合利用频率域和时间域信息进行地震映像数据解释的效果.时频分析方法提取了地震波的频谱中关于地层岩性、构造方面的信息,为地震映像数据的处理和解释提供了更多的参考信息.实例证明,利用时频分析解释地震映像数据,有助于了解覆盖层下岩性变化、薄层的分布范围、探测隐伏土洞、确定混凝土构件中缺陷位置,提高地震映像数据的解释精度和准确性.     

一种新的针对反射波的逆时偏移真振幅成像条件

真振幅成像是一种代表性的定量估计模型参数扰动高波数部分的地震波成像方法.经典的真振幅成像方法在高频近似和理想照明假设条件下求取显式对角Hessian逆矩阵作为偏移振幅加权算子,用以校正波传播过程中的几何扩散效应,得到模型参数扰动的带限估计.真振幅保真成像方法在利用逆时偏移（RTM）框架实现时会产生低波数噪声,影响对高波数参数估计的精度.本文给出了一种新的基于RTM框架的真振幅保真成像条件,该成像条件针对反射波数据,在高频近似下散射模式对应正问题及Bayes反问题框架下导出.与传统基于高频渐进反演的波动方程成像方法类似,利用本文提出RTM成像条件能够保证计算结果与高频近似下反演结果的一致性.同时,利用本文提出RTM真振幅成像条件能够在成像过程中自动保真的消除传统真振幅RTM算法中存在低波数噪声,模型数值实验结果验证了本文方法的正确性和有效性.

     

一种新的针对反射波的逆时偏移真振幅成像条件

真振幅成像是一种代表性的定量估计模型参数扰动高波数部分的地震波成像方法.经典的真振幅成像方法在高频近似和理想照明假设条件下求取显式对角Hessian逆矩阵作为偏移振幅加权算子,用以校正波传播过程中的几何扩散效应,得到模型参数扰动的带限估计.真振幅保真成像方法在利用逆时偏移（RTM）框架实现时会产生低波数噪声,影响对高波数参数估计的精度.本文给出了一种新的基于RTM框架的真振幅保真成像条件,该成像条件针对反射波数据,在高频近似下散射模式对应正问题及Bayes反问题框架下导出.与传统基于高频渐进反演的波动方程成像方法类似,利用本文提出RTM成像条件能够保证计算结果与高频近似下反演结果的一致性.同时,利用本文提出RTM真振幅成像条件能够在成像过程中自动保真的消除传统真振幅RTM算法中存在低波数噪声,模型数值实验结果验证了本文方法的正确性和有效性.     

一种新的地震子波提取与层速度反演方法

粒子群优化算法是近十年发展起来的一种基于群智能的非线性全局最优化新方法.本文详细介绍了粒子群优化算法的基本原理,并将其应用到子波提取与层速度反演中.通过模拟数值算例,从不同角度研究了粒子群优化算法的可行性及其效率问题.试算结果表明,粒子群优化算法在不同分辨率、不同信噪比、不同相位子波合成的地震记录反演中效果明显.     

二维弹性多波时空域高斯束偏移方法

随着我国勘探开发难度逐步增大,勘探目标开始向裂缝油气藏、岩性油气藏等复杂探区转移,研究高精度、适应性强的多波多分量深度偏移算法在后续的地震解释、属性分析及储层预测中具有重要意义.针对多波多分量地震数据,本文提出了一种二维弹性波时空域高斯束偏移方法.时空域高斯束沿中心射线传播时能够面向成像目标描述局部波场,且对振幅和频率可调制的Gabor基函数有天然的适应性,因而将基于Gabor分解的子波重构方法应用于震源波场构建,从而得到任意点源函数产生的时空域高斯束波场.该方法由于直接在时间域进行计算,可以避开频率域中出现的假频和边缘截断效应等问题.基于各向同性弹性波动方程的Kirchhoff-Helmholtz积分解,利用矢量时空域高斯束传播算子构建格林函数和格林位移张量,并结合上行射线追踪策略,实现了检波点波场的反向延拓.针对矢量波成像问题,本文借鉴弹性波逆时偏移方法从矢量延拓波场中分离出纯纵波分量和纯横波分量,进而采用修改后的内积成像条件产生具有明确物理意义的PP、PS成像结果,避免了转换波成像的极性反转问题.最后利用简单两层模型和不含盐体构造的部分Sigsbee2a模型的成像结果,并将其与应用近似纵横波成像条件、标量和矢量势成像条件的偏移剖面进行对比,验证了本文方法的正确性和有效性.

     

呼和浩特—包头盆地岩石圈细结构的深地震反射探测

跨呼和浩特-包头盆地(以下简称"呼包盆地")完成的91.8 km长的深地震反射剖面,揭示了呼包盆地的岩石圈精细结构和断裂的深、浅构造特征.结果表明,本区地壳和岩石圈具有清晰的层状反射结构特征,其中,地壳厚度约45~48 km,岩石圈厚度约82~87 km.莫霍面在大青山之下出现约3.5 km的抬升,暗示大青山的隆升不是因为地壳物质增厚所致,即大青山可能不存在"山根".呼包盆地为南浅、北深的"箕状"断陷盆地,盆地沉积层最厚处位于大青山山前,其厚度约为7~8 km.鄂尔多斯北缘断裂和大青山山前断裂作为呼包盆地的南、北边界断裂,在剖面上均表现为由3~4条断裂组成的"Y"字形断裂构造,它们对呼包盆地的形成、地层沉积、基底变形和地震活动都有重要的控制作用.剖面揭示的岩石圈深断裂位于大青山山前断裂的下方,该断裂向上进入上地壳,向下切割中-下地壳、莫霍面,进入上地幔.深断裂的存在为深部热物质的上涌与能量强烈交换提供了通道,而上涌的软流层物质与岩石圈地幔发生交代和侵蚀作用导致岩石圈减薄.     

IMS体系抗震性能研究的Push-over方法

应用三维有限元实体单元计算模型，通过Push-over方法对云南傣族新民居IMS体系结构进行了地震破坏历程分析，并与模型振动台试验结果进行了比较。三维实体单元Push-over方法结果能较好的反映结构破坏表象，对结构抗震性能研究具有很好的辅助作用。     

由地震分布丛集性给出断层参数的一种新方法

由于大范围内地质构造的复杂性和介质的非均匀性,发震断层面的几何形态一般十分复杂.如果大地震的破裂过程涉及多个断层的活动,则发震断层并非是单一断层平面,而是多个断层面的组合.利用地震空间位置分布丛集性,即震源点成丛位于断层面附近的假设,结合稳健扩充算法和主成分分析给出一种可以重构活断层网络三维空间结构的新方法.该方法每次从震源点集中处开始,利用假设检验扩充子断层面,并得到多个子断层面.接着按震源点属于最近断层面的准则把各子断层面内的震源点进行竞争,并根据一定假设合并和删除一些子断层面,最后用主成分分析确定每个子断层面参数.于是可根据地震事件目录给出一组矩形区域来描述断层面网络结构,其中每个矩形断层面由其位置、走向和倾角确定.通过计算机模拟发现,新方法可成功地重建模拟地震目录的断层面,最后用于南加州1992年6月28日发生的Landers地震部分余震目录中,得到各个子断层面参数与已知地质破裂或隐伏断层相当一致.