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1.
近年来发展的新型地震观测系统--分布式光纤声波传感器(DAS,Distributed Acoustic Sensing)可以实现低成本高密度观测,有望提高浅层结构成像的精度以及分辨率.最近国内研发了一系列具有自主知识产权的DAS设备,为验证国产设备在浅层结构研究中的可行性以及应用效果,2018年7月我们开展了一次DAS观测实验.实验采集了50kg落锤震源激发的地震信号,并采用多道面波分析方法提取了8~20Hz频段的主动源Rayleigh波相速度频散曲线,得到了实验区浅层30m的S波速度结构.获得的主动源面波频散曲线与共址检波器的结果吻合,也与背景噪声提取的结果具有较好的一致性,表明国产设备的可靠性和DAS在浅层结构主动源面波成像研究中的可行性. 相似文献
2.
随着城市化的发展,城市地球物理日益成为地球物理研究的重要方向,地震成像是构建城市地下空间三维/四维图像的重要手段,但面临观测成本高的困难.近年来国际上新发展的分布式光纤声波传感器作为高密度地震观测系统已经在地震层析成像方面得到了应用,在提高成像分辨率的同时,又降低了观测成本.本研究使用国产分布式光纤声波传感器开展了观测实验,利用480m埋地光缆记录了13h背景噪声,计算得到噪声互相关函数,获得了高频Rayleigh面波信号.采用多道面波分析方法提取相速度频散曲线,其结果与传统检波器记录和主动源结果较为一致.采用遗传算法反演得到了研究区内二维S波速度剖面,获得了下方沉积物横向变化特征.通过本次实验,初步验证了国产设备开展地震背景噪声成像研究、构建地下浅层结构模型的可行性. 相似文献
3.
浅层地震反射波法和面波方法是两种相互独立发展的地震勘探方法,在各自的数据采集和处理中,对方都是作为干扰信号而存在. 本文利用浅层地震反射资料中被视为干扰的面波信号,通过成熟的多道面波勘探技术处理浅层地震反射资料,在频率-波数域中提取多阶振型面波的频散曲线,并基于该曲线反演浅地表S波速度结构. 这种方法充分开发利用了已有数据,无需单独的面波数据采集系统,同时为解释浅层地震反射资料提供了额外的信息约束. 结果表明:浅层地震反射资料中可提取出可靠的多阶振型面波频散曲线,并能给出稳定的反演结果,同时,面波反演的多解性可以通过高阶振型反演得以进一步约束;低速层的存在是观测频散曲线出现振型跳跃或呈“之”字形回折的必要条件而非充分条件. 相似文献
4.
Rayleigh面波的频散特性可以用来研究地表浅层结构. 本文使用时域有限差分法来模拟复杂黏弹性介质中的Rayleigh面波,研究了Q值对面波频散特性的影响.文中采用旋转交错网格有限差分,以非分裂卷积形式的完全匹配层为吸收边界,推出了求解二阶位移-应力各向同性黏弹性波动方程的数值方法.为了检验数值解的精度,首先将简单模型的正演结果与解析解对比,验证了方法的正确性;然后模拟了横向缓变层状介质和含有洞穴的介质中的面波,对弹性和黏弹性介质中的面波的频散特性进行对比分析.模拟结果表明浅层Q值对面波的频散特性有显著的影响;强吸收情况下,高阶面波的能量相对低阶面波能量显著增强. 相似文献
5.
Myrto Papadopoulou Federico Da Col Binbin Mi Emma Bäckström Paul Marsden Bojan Brodic Alireza Malehmir Laura Valentina Socco 《Geophysical Prospecting》2020,68(1):214-231
In mineral exploration, increased interest towards deeper mineralizations makes seismic methods attractive. One of the critical steps in seismic processing workflows is the static correction, which is applied to correct the effect of the shallow, highly heterogeneous subsurface layers, and improve the imaging of deeper targets. We showed an effective approach to estimate the statics, based on the analysis of surface waves (groundroll) contained in the seismic reflection data, and we applied it to a legacy seismic line acquired at the iron-oxide mining site of Ludvika in Sweden. We applied surface-wave methods that were originally developed for hydrocarbon exploration, modified as a step-by-step workflow to suit the different geologic context of hard-rock sites. The workflow starts with the detection of sharp lateral variations in the subsurface, the existence of which is common at hard-rock sites. Their location is subsequently used, to ensure that the dispersion curves extracted from the data are not affected by strong lateral variations of the subsurface properties. The dispersion curves are picked automatically, windowing the data and applying a wavefield transform. A pseudo-2D time-average S-wave velocity and time-average P-wave velocity profile are obtained directly from the dispersion curves, after inverting only a reference curve. The time-average P-wave velocity profile is then used for the direct estimation of the one-way traveltime, which provides the static corrections. The resulting P-wave statics from the field data were compared with statics computed through conventional P-wave tomography. Their difference was mostly negligible with more than 91% of the estimations being in agreement with the conventional statics, proving the effectiveness of the proposed workflow. The application of the statics obtained from surface waves provided a stacked section comparable with that obtained by applying tomostatics. 相似文献
6.
The Yellowstone volcano is one of the largest active volcanoes in the world, and its potential hazards demand detailed seismological and geodetic studies. Previous studies with travel time tomography and receiver functions have revealed a low-velocity layer in the crust beneath the Yellowstone volcano, suggesting the presence of a magma chamber at depth. We use ambient seismic noise from regional seismic stations to retrieve short-period surface waves and then study the shallow shear velocity structure of the Yellowstone region by surface wave dispersion analysis. We first obtained a crustal model of the area outside of the Yellowstone volcano and then constructed an absolute shear wave velocity structure in combination with receiver function results for the crust beneath the Yellowstone volcano. The velocity model shows a low-velocity layer with shear velocity at around 1.3 km/s, suggesting that a large-scale magma chamber exists at shallow levels within the crust of the Yellowstone volcanic region. 相似文献
7.
晋冀鲁豫交界地区位于华北克拉通的东南部, 研究该区地壳结构有助于进一步了解河北南部及其邻区地质构造演化特征、 发震机制、 发震规律。 本文收集了晋冀鲁豫交界地区两年84个地震台连续波形观测资料, 通过台站对波形互相关, 得到各台站对间的经验格林函数, 再利用图像分析技术提取瑞利波频散曲线。 本文基于面波直接成像方法得到不同深度剪切波速度结构。 结果显示, 该区部分速度异常与该区地表地质构造单元存在相关性, 速度异常呈区域分布特征, 山区和盆地呈现非常显著的速度差异, 浅层上地壳结构速度变化特征与沉积层厚度、 结晶基底埋深等区域构造密切相关, 中下地壳及上地幔存在不规则的速度异常, 与该区的地震发生存在相关性。 相似文献
8.
在近二十年来,多道面波分析法(MASW)由于其便捷、高效等特性在浅层地震勘探领域得到了广泛的应用.本文基于多道面波勘探的采集方式,提出了一种新的面波多道分析方法——矢量波数变换法(VWTM).该方法通过对震源的近似,基于水平层状模型得到台站与震源间近似格林函数,然后进行矢量波数变换得到含有高阶模态Rayleigh波(频率-相速度)频散能量图.本研究首先利用合成地震数据到频散能量图与理论频散曲线进行叠加分析该方法的有效性和正确性;然后与相移法进行对比分析,我们发现在频散能量图中VWTM法对基阶、高阶模态成像均具有更高的分辨率和成像质量;最后我们将其应用于实际多道瞬态面波探测中,通过与相移法进行对比分析,发现VWTM法是一种方便、实用、有效的Rayleigh波频散提取方法.VWTM法提取多模态的Rayleigh波频散特征具有巨大潜力,可为基阶、高阶面波频散联合反演提供丰富的高阶模态频散信息. 相似文献
9.
2015年8月12日天津滨海新区发生的强烈化学品爆炸造成了巨大的经济损失和社会影响.天津爆炸产生了清晰的大振幅面波信号,分析结果表明这组信号由基阶和高阶面波组成,可以追踪到约135 km外的远处台站.利用这组面波信号分别开展了以下研究：（1）利用附近三个台站记录的四个单频基阶Rayleigh波信号对爆破事件的绝对位置进行了网格搜索,结果与利用GPS测量的位置相差仅0.498 km;（2）分别利用网格搜索和主事件定位法,对两次子事件的相对位置进行了确定,距离约75 m左右,与前人研究结果吻合;（3）从面波记录中测量到36条基阶Rayleigh波、49条第一高阶Rayleigh波、9条基阶Love波和29条第一高阶Love波的频散曲线,并进一步反演获得研究区域地下4 km内的S波速度结构.反演结果显示地表处S波速度低至0.375 km·s-1,在小于1 km的浅地表速度梯度较大,符合典型的盆地结构特征.本文的研究结果为类似爆炸等突发事件快速定位提供了新的思路,有助于灾后救援的迅速展开;同时得到天津滨海新区及周边浅层精细的速度结构,对于地震灾害评估有很大帮助. 相似文献
10.
Estimated Green's function (EGF) between stations has been extracted from ambient seismic noise, direct surface wave and coda waves. It is also confirmed by laboratory experiments on ultrasonics and theoretical derivations assuming diffusive wave field, equi-partition of modes or random sources on an enclosed surface. This method provides a new approach to study the crust and mantle structure at regional scale, continental scale and global scale. Following the achievements with seismometer records, the records of infrasonic station, hydrophone and microphone were also used to obtain the EGFs of different wave fields. Since superconducting gravimeter is a better long period instrument than regular seismometer, EGF at longer period is expected to be obtained with the cross correlation of gravity data. In this paper, we will show the EGFs extracted by cross-correlations between the superconducting gravimeters and the seismometers. Both the travel times and dispersion curves obtained from different data types are consistent. The result shows that it is possible to retrieve the deep structure by the cross correlation of gravity data. 相似文献
11.
Marc Wathelet Denis Jongmans Matthias Ohrnberger Sylvette Bonnefoy-Claudet 《Journal of Seismology》2008,12(1):1-19
Valuable information about one-dimensional soil structures can be obtained by recording ambient vibrations at the surface,
in which the energy contribution of surface waves predominates over the one of other types of waves. The dispersion characteristics
of surface waves allow the retrieval of the shear-wave velocity as a function of depth. Microtremor studies are usually divided
in two stages: deriving the dispersion (or auto-correlation) curve from the recorded signals and inverting it to obtain the
site velocity profile. The possibility to determine the dispersion curve over the adequate frequency range at one site depends
on the array aperture and on the wavefield spectra amplitude that can be altered by filtering effects due to the ground structure.
Microtremors are usually recorded with several arrays of various apertures to get the spectral curves over a wide frequency
band, and different methods also exist for processing the raw signals. With the objective of defining a strategy to achieve
reliable results for microtremor on a shallow structure, we analyse synthetic ambient vibrations (vertical component) simulated
with 333 broadband sources for a 25-m deep soil layer overlying a bedrock. The first part of our study is focused on the determination
of the reliable frequency range of the spectral curves (dispersion or auto-correlation) for a given array geometry. We find
that the wavenumber limits deduced from the theoretical array re sponse are good estimates of the valid spectral curve range.
In the second part, the spectral curves are calculated with the three most popular noise-processing techniques (frequency–wavenumber,
high-resolution frequency–wavenumber and spa tial auto-correlation methods) and inverted indi vidually in each case. The inversions are
performed with a tool based on the neighbour hood algorithm that offers a better estimation of the global uncertainties than
classical linearised methods, especially if the solution is not unique. Several array apertures are necessary to construct
the dispersion (auto-correlation) curves in the appropriate frequency range. Considering the final velocity profiles, the
three tested methods are almost equivalent, and no significant advantage was found for one particular method. With the chosen
model, all methods exhibit a penetration limited to the bedrock depth, as a consequence of the filtering effect of the ground
structure on the vertical component, which was observed in numerous shallow sites. 相似文献
12.
Feasibility of waveform inversion of Rayleigh waves for shallow shear-wave velocity using a genetic algorithm 总被引：1，自引：0，他引：1
Chong Zeng Jianghai Xia Richard D. MillerGeorgios P. Tsoflias 《Journal of Applied Geophysics》2011,75(4):648-655
Conventional surface wave inversion for shallow shear (S)-wave velocity relies on the generation of dispersion curves of Rayleigh waves. This constrains the method to only laterally homogeneous (or very smooth laterally heterogeneous) earth models. Waveform inversion directly fits waveforms on seismograms, hence, does not have such a limitation. Waveforms of Rayleigh waves are highly related to S-wave velocities. By inverting the waveforms of Rayleigh waves on a near-surface seismogram, shallow S-wave velocities can be estimated for earth models with strong lateral heterogeneity. We employ genetic algorithm (GA) to perform waveform inversion of Rayleigh waves for S-wave velocities. The forward problem is solved by finite-difference modeling in the time domain. The model space is updated by generating offspring models using GA. Final solutions can be found through an iterative waveform-fitting scheme. Inversions based on synthetic records show that the S-wave velocities can be recovered successfully with errors no more than 10% for several typical near-surface earth models. For layered earth models, the proposed method can generate one-dimensional S-wave velocity profiles without the knowledge of initial models. For earth models containing lateral heterogeneity in which case conventional dispersion-curve-based inversion methods are challenging, it is feasible to produce high-resolution S-wave velocity sections by GA waveform inversion with appropriate priori information. The synthetic tests indicate that the GA waveform inversion of Rayleigh waves has the great potential for shallow S-wave velocity imaging with the existence of strong lateral heterogeneity. 相似文献
13.
14.
GUO Yang XU Jiajun LIN Chen JIN Xing YAO Huajian YANG Hongfeng CAI Huiteng 《中国地震研究》2019,33(2):265-275
112 short-period seismographs were set up in the 400km2 area of Pingtan Island and its surrounding areas in Fujian. The combined observations of the airgun source and ambient noise source were carried out using a dense array to receive the 387 airgun signals excited around the island and one month of continuous ambient noise recording. The 1-D P-wave and S-wave shallow velocity model of Pingtan Island is obtained by the inversion of the airgun body wave''s first arrival time data, and the reliability of the velocity model is verified by using the surface wave phase velocity dispersion curve, which can provide initial model for subsequent 3-D imaging. The experimental results show that this experiment is a successful demonstration of local scale green non-destructive detection, which can provide basic data for shallow surface structure research and strong vibration simulation of the Pingtan Island. 相似文献
15.
结合汶川地震断裂带动态监测,利用快速响应探测系统,开展了断层带浅部结构人工地震探测.针对地震断裂带动态监测条件下的复杂波场和低信噪比的情况,在f-k波场分离的基础上,分别利用了折射波共中心点成像、面波速度反演、反射波叠加成像方法,进行了浅层断层和构造成像处理,并对处理结果进行了综合解释,给出了断裂带浅部断层分布和速度特征.为汶川地震龙门山断裂带东北端动态监测提供了基础结构信息,所发展的断裂带快速响应探测技术对于地震应急动态监测具有重要意义. 相似文献
16.
为了对比天然源面波勘探不同台阵布局的探测效果, 筛选出探测成果可靠、 效率高和便于野外施工的天然源面波勘探台阵阵形, 在天水市黄土覆盖区的同一场地分别用4种常见的阵形进行数据采集试验, 并对各种阵形数据使用空间自相关法或扩展空间自相关法提取相应的频散曲线, 通过反演得到了试验点地下的浅层速度结构模型. 分析对比试验结果表明: 4种台阵提取的频散曲线数值很相近; 频散谱能量集中度较高的是嵌套式等边三角形和圆形台阵, L形和直线形台阵相对分散; L形台阵低频段(4—8 Hz)比直线形台阵差, 其高频段(8—40 Hz)比直线形台阵好. 针对直线形台阵在高频段信噪比较低的情况, 在确保探测成果可靠性的前提下, 为了提高探测效率, 提出了在同一直线形台阵开展天然源与人工源面波联合勘探的数据采集方法. 实验结果证实, 这种联合勘探方法不仅可弥补直线形台阵高频段的不足, 确保探测精度和结果的可靠性, 而且还能实现“高低”频兼顾, 即“深浅”兼顾. 相似文献
17.
面波成像是研究地壳上地幔横波速度结构的一种重要方法．通常,面波相速度或群速度成像假设面波沿大圆路径传播．但是,在地下介质速度结构变化较大时,面波会偏离大圆路径传播,从而导致基于大圆路径假设下的面波成像结果存在一定的误差. 我们采用基于射线追踪的面波成像方法,研究了面波的偏离大圆路径传播对四川西部地区面波相速度成像结果的影响．使用快速行进法(fast marching method)进行面波传播路径的射线追踪,采用子空间反演法(subspace inversion)进行迭代反演,对理论模型合成数据和川西台阵的短周期背景噪声相速度频散数据进行成像分析,并与使用大圆路径传播的成像结果进行对比．对理论模型的测试结果表明,当速度结构变化较大时,基于偏离大圆路径传播的面波成像能够更好地恢复模型异常．对川西台阵的真实数据反演结果显示:在短周期为6 s时,基于偏离大圆路径传播的反演方法较基于大圆路径传播的反演方法所获得的相速度异常的幅度更大些,在四川盆地区域两者的差异接近0.2 km/s;在周期为10 s时,两种反演方法的差异显著减小,基本都在0.1 km/s以内．这主要是因为6 s周期的面波相速度对复杂的上地壳浅层结构更为敏感,从而使得面波的偏离大圆路径传播效应对反演结果的影响更为显著．本文结果表明,当某一周期不同路径的面波相速度测量值变化较大,例如相对于平均相速度的异常超过10％时,则需考虑采用基于偏离大圆路径传播的面波成像方法,否则速度异常较大区域的反演结果可能会造成较大的偏差． 相似文献
18.
浅层面波法调查表层速度结构多用于非沙漠区的工程与环境领域。本文利用多道面波分析(MASW)技术针对塔克拉玛干沙漠地区特殊地质情况,对所采集的浅层多道面波资料进行处理分析得到沙漠区表层速度结构;同时对该地区所获得的地震大炮记录上的面波进行了处理、分析和对比,探讨了沙漠区利用大炮面波法调查表层结构的可行性。实践表明,多道面波资料可以得到很好的浅层速度结构,而大炮记录则可得到详尽的深层地质结构,将二者相结合便得到测区表层60m范围内的速度结构信息,也证明了在沙漠区利用大炮面波记录提取表层地下介质结构是可行的。 相似文献
19.
Studying surface structure in desert areas using multiple kinds of surface wave data 总被引：1，自引：0，他引：1
Shallow surface wave methods are mostly used for investigation of the surface velocity structure in environmental and engineering geophysics in non-desert areas. For the special geological features of the Takelamagan Desert area, we use the multi-channel analysis of surface wave （MASW） method to process multi-channel shallow surface wave records to determine the near surface velocity structure in the desert area. We also process, analyze, and compare the surface waves in many-trace records extracted from the oil exploration shot gathers in the area. We show that the MASW method can determine detailed shallow velocity structure in desert areas and the many-trace records can be used to get detailed deep geological structure. The combination of the two different datasets can obtain the exact velocity structure upper 60 m depth in the survey area. 相似文献
20.
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