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1.
在地震勘探中,Ｐ波和Ｓ波入射到一固体液体分界面处时,在该分界处的水平检波器和垂直检波器将接受到相位的响应垂直的响应。垂直检波器的响应与在自由界面处的垂直检波器 响应大概相同,而水平检波器对Ｐ波的响应相对于对Ｓ波的 来说要强。 相似文献
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In recent years some authors have given a certain amount of attention to towed seismic reflection acquisition systems. Based on some of these works we sought to design and test a system making use of currently available geophones instead of specifically designed sensors as employed in some previous works. Thus, bearing in mind that the geophone's characteristics are achieved in the conditions that they are originally designed to be employed in, i.e., coupled with a spike driven into the ground, we devoted our attention to some of the variables involved in the geophone's performance, namely the total weight, the effect of a spikeless geophone and the surfaces on which the geophone is placed. Previously, we had experimentally verified some variations in the signal response due to coupling geophones in different surface materials, such as hard soil, asphalt and concrete pavement and we noticed that these surface materials were in fact an important factor in the overall response. Hence, these materials, or as we also called them coupling agents, could be employed as a base material in the construction of a mobile seismic acquisition device composed of blocks of a certain size, on which the geophone would be then inserted and thus making it into a spikeless surface towable system. Therefore, various materials were tested in order to select one that could maintain a similar fidelity to that of the spike coupled geophone and thus contribute towards building a more time efficient and towable geophone and block system. Pinging tests revealed variations in the coupling frequency and damping characteristics of each coupling agent and from all of these tested materials one was selected for field comparative tests with the normally planted geophones with spike coupling. Finally a seismic reflection profile was acquired simultaneously with both systems, i.e., spike coupling versus cement block coupled geophones. This field test showed similar results in terms of signal levels and frequency content and therefore it was possible to observe the presence of the same reflectors and other seismic events in either of the time sections. With this experiment we propose not only a system that allows a time efficient seismic field operation but we also aim to encourage more research into the response dependency of the coupling agent of which the towable base block is made of. 相似文献
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We introduce a method to detect and compensate for inconsistent coupling conditions that arise during onshore seismic data acquisitions. The reflected seismic signals, the surface waves, or the ambient-noise records can be used for the evaluation of the different coupling conditions of closely spaced geophones. We derive frequency-dependent correction operators using a parametric approach based upon a simple model of the interaction between geophone and soil. The redundancy of the measurements available permits verification of the assumptions made on the input signals in order to derive the method and to assess the validity of the model used. The method requires point-receiver data in which the signals recorded by the individual geophones are digitized. We have verified the accuracy of the method by applying it to multicomponent ambient-noise records acquired during a field experiment in which the coupling conditions were controlled and modified during different phases of the experiment. We also applied the method to field data, which were acquired without the coupling conditions being controlled, and found that only a few geophones showed an anomalous behaviour. It was also found that the length of the noise records routinely acquired during commercial surveys is too short to provide enough statistics for the application of our method. 相似文献
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Faithful recording of the elastic wavefield at the sea‐bed is required for quantitative applications of 4C seismic. The accuracy of the recorded vectorial wavefield depends on factors that vary from deployment to deployment. This paper focuses on one such factor: the interaction of the acquisition system with the sea‐bed, which is referred to here as coupling. We show, using multi‐azimuth data recorded with a cable‐based sea‐bed acquisition system, whose sensor housing is cylindrically shaped and with the in‐line geophone fixed to the cable, that coupling depends on the propagation direction and wave type (P‐ or S‐waves) of the incident wavefield. We show that coupling is more critical for S‐waves than for P‐waves. Detection of inconsistent coupling using both P‐ and S‐waves is therefore mandatory. A data‐driven processing method to compensate for the frequency‐dependent coupling response of the cross‐line geophone is derived. Its application to field data verifies the effectiveness of the method. 相似文献
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电磁驱动式可控震源在城市浅层地震勘探中所面临的最突出的困难是微弱的反射信号常常淹没在很强的背景噪声之中.为了提高地震记录的信噪比,可以利用多台可控震源阵列实施相位控制形成定向地震波束以增强地震波的能量.本文讨论这种相控阵震源的波束形成机制.引入了地震波场的边际能量密度的概念,利用地震波场的时间切片技术,对模型空间各个方向上的能量强度进行了定量分析.用有限差分法对相控阵震源Chirp信号扫描的地震响应进行了数值模拟.当定向地震波束的汇聚带与观测排列的空间范围相一致时,相控阵震源合成地震记录的能量强度要显著高于单个可控震源情形的能量强度,波形振幅的均匀性要明显优于常规组合激发震源情形波形振幅的均匀性. 相似文献
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Seismic acquisition can be costly and inefficient when using spiked geophones. In most cases, such as the desert, the most practical solution is the use of flat bases, where geophone‐ground coupling is based on an optimal choice of the mass and area of contact between the receiver and the ground. This optimization is necessary since areas covered by sand are loose sediments and poor coupling occurs. Other cases include ground coupling in stiff pavements, for instance urban areas and ocean‐bottom nodes. We consider three different approaches to analyse coupling and model the geophone with a flat base (plate) resting on an elastic half‐space. Two existing models, based on the full‐wave theory, which we refer to as the Wolf and Hoover‐O'Brien models, predict a different behaviour with respect to the novel method introduced in this work. This method is based on the transmission coefficient of upgoing waves impinging in the geophone‐ground contact, where the ground is described as an anelastic half‐space. The boundary conditions at the contact have already been used to model fractures and are shown here to provide the equation of the damped oscillator. This fracture‐contact model depends on the stiffness characteristic of the contact between the geophone base plate and the ground. The transmission coefficient from the ground to the plate increases for increasing weight and decreasing base plate area. The new model predicts that the resonant frequency is independent of the geophone weight and plate radius, while the recorded energy increases with increasing weight and decreasing base plate area (as shown from our own experiments and measurements by Krohn) which is contrary to the theories developed by Wolf and Hoover‐O'Brien. The transient response is obtained by an inverse Fourier transform. Optimal geophone‐ground coupling and energy transmission are required, the first concept meaning that the geophone is following the motion of the ground and the second one that the signal is detectable. As a final example, we simulate seismic acquisition based on the novel theory, showing the differences between optimal and poor ground‐to‐geophone energy transmission. 相似文献
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The estimation of the quality factor Q plays a fundamental role in enhancing seismic resolution via absorption compensation in the near-surface layer. We present a new geometry that can be used to acquire field data by combining surface and cross-hole surveys to decrease the effect of geophone coupling on Q estimation. In this study, we drilled number of receiver holes around the source hole, each hole has different depth and each geophone is placed geophones into the bottom of each receiver hole to avoid the effect of geophone coupling with the borehole wall on Q estimation in conventional cross-hole seismic surveys. We also propose a novel tomographic inversion of the Q factor without the effect of the source signature, and examine its stability and reliability using synthetic data. We estimate the Q factors of the near-surface layer in two different frequency bands using field data acquired in the Dagang Oilfield. The results show that seismic absorption in the near-surface layer is much greater than that in the subsurface strata. Thus, it is of critical practical importance to enhance the seismic solution by compensating for near-surface absorption. In addition, we derive different Q factors from two frequency bands, which can be treated, to some extent, as evidence of a frequency-dependent Q. 相似文献
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In two-component seismic observations with vertical and in-line horizontal geophones, the compressional (P-) wave amplitudes, as well as the vertically polarized shear (SV-) wave amplitudes, are observed on both vertical and horizontal geophones. In our case, we use a P-wave source, while the SV waves are the result of mode conversion. The mode-conversion mechanism considered here is related to the near-surface layers, i.e. we have a P-leg from the source and mode conversion at/in the weathered layer. The resulting SV waves therefore will show lateral variations because the elastic parameters of the near-surface layers vary along the seismic line, but these variations will be consistent at the surface. This effect is demonstrated by a synthetic example based on elastic parameters representative of the actual seismic line being considered. To separate the individual P and SV arrivals, we apply a two-dimensional convolution filter designed to meet the wavenumber-frequency (k-f) domain transfer function for P-SV separation which can be derived from thek-f domain geophone-receiving characteristic and the near surface P- and S-wave velocities. The reason for P-SV separation filtering in the offset-traveltime (X-T) domain instead of directly filtering in thek-f domain, is a great saving in computer time, asX-T filters, with few coefficients, can be used. In this paper, after a short summary of thek-f domain P-SV separation filters and their transformation to theX-T domain, we apply theX-T filters to synthetic data in order to demonstrate that our design is correct. We also work on actual data and discuss the problems being faced, which mainly, originate from the different geophone groups and, as a consequence, the different scalings of vertical and horizontal geophones. The main advantage of two-component seismic observations is two-fold: firstly, a clean P-wave section is obtained (SV-energy arriving at the receivers is cancelled by applying the foresaid separation filter) and, secondly we obtain an additional SV-wave section at almost no cost to data acquisition. These two sections contribute towards distinguishing between true and false bright spots, so they are, used as direct hydrocarbon indicator tools. 相似文献
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Previously ignored characteristics of the seismic recording instrument are presently experienced as limitations as more sophisticated interpretive methods using wider frequency ranges are developed to extract stratigraphic information from seismic land data for hydrocarbon and mineral exploration. Most of these limitations arise from inadequate characteristics of the first element of the seismic instrument: the geophone. A geophone does not faithfully follow the motion of the earth for higher frequencies due to poor geophone-earth coupling. This filtering effect brings about time shifts that are dependent on the frequency and the soil type. A geophone can also produce spurious outputs, brought about by the motion of the suspended part of the geophone, with a magnitude comparable to that of the desired output. The suspension is made very compliant to obtain the required sensitivity. A compliant suspension, however, gives a large sag. The geophone can therefore only be used in one position, tolerating little tilt. A compliant suspension also widens the traveling range of the movable part. Minor sensitivity changes with travel are then noticeable as nonlinearity, since the surface wave is large with respect to the reflected wave. A compliant suspension is usually realized in the form of thin, spirally shaped spring-spiders. Such suspensions exhibit transverse or rotational resonances that are in or close to the seismic frequency band. Excited by ground roll, they can produce considerable undesirable output. The novel geophone we describe is a light-weight (17 g) acceleration-sensitive transducer which gives good ground coupling and partial correction for the increasing damping in the earth with increasing frequencies. It employs internal hybrid electronics for a magnetodynamic velocity-nulling feedback system. Velocity nulling makes the movable part of the geophone virtually rigid with respect to the housing. This makes the geophone characteristics independent of the suspension. The springs used are stiff in a transverse and rotational direction so that the suspension resonances are well outside the useful frequency band. This suspension also allows the geophone to be used in any orientation while being only sensitive to the vibration component along the main axis. The feedback system makes the sensitivity flat within 1 dB from 2 Hz to 500 Hz, with a phase tolerance smaller than 5°. The geophone is robust, has no moving internal wires, employs a current output [sensitivity 1 mA/(m s?2)] and internal gain so that the signal-to-cable-noise ratio is improved. This type of output allows parallel connection without any interaction between the geophones. 相似文献
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By summing geophone and hydrophone data with opposite polarity responses to water layer reverberation, the ocean bottom cable dual-sensor acquisition technique can effectively eliminate reverberation, broaden the frequency bandwidth, and improve both the resolution and fidelity of the seismic data. It is thus widely used in industry. However, it is difficult to ensure good coupling of the geophones with the seabed because of the impact of ocean flow, seafloor topography, and field operations; therefore, geophone data are seriously affected by the transfer function of the geophone-seabed coupling system. As a result, geophone data frequently have low signal-to-noise ratios (S/N), which causes large differences in amplitude, frequency, and phases between geophone and hydrophone data that severely affect dual-sensor summation. In contrast, the hydrophone detects changes in brine pressure and has no coupling issues with the seabed; thus, hydrophone data always have good S/N. First, in this paper, the mathematical expression of the transfer function between geophone and seabed is presented. Second, the transfer function of the geophone-seabed is estimated using hydrophone data as reference traces, and finally, the coupling correction based on the estimated transfer function is implemented. Using this processing, the amplitude and phase differences between geophone and hydrophone data are removed, and the S/N of the geophone data are improved. Synthetic and real data examples then show that our method is feasible and practical. 相似文献
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本文分析了海陆两栖地带地震勘探中同时使 用的速度检波器和加速度检波器存在的差异及其对 地震信号的影响;在此基础上,设计研制出了陆用 压电检波器,并对其性能特点进行了分析;通过试 验资料分析,消除了海陆两种不同机理的检波器资 料的相位差的问题,陆用压电检波器和水中压电检 波器记录信号的频带和能量达到一致,提高了地震 资料的分辨率;实现了海陆地区可以同时采用相同 机理的检波器进行地震信号的接收,解决了滩海地 区速度检波器和加速度检波器长期混用的问题。 相似文献
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地震检波器受到地面横向运动激励时的输入输出关系定义为检波器的横向灵敏度特性.本文对检波器线圈受到横向激励时产生的轴向振动进行了分析.可以看到,当悬挂线圈的弹簧片悬丝发生动力失稳时,检波器的横向灵敏度突然增大;在线圈横向振幅很小的情况下,失稳频率接近悬丝的横向固有频率.利用谱分析技术可以准确地从检波器噪声中检测出检波器的横向灵敏度和失稳频率,即检波器假频. 相似文献
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《Journal of Applied Geophysics》2006,58(2):87-98
A geophysical campaign to characterize the subsurface of a contaminated site down to a depth of several tens of meters was carried out under the HYGEIA-CEE project. On this site, seismic techniques were combined to image the geological structures; i.e. seismic reflection, P-wave tomography and spectral analysis of surface waves. Because these techniques consider different wave components in the processing, they can be expected to provide complementary information concerning the site lithology. The special feature of this experiment is the fact that the same seismic acquisition device, consisting of a mobile central unit, a drop-weight seismic source, and a sensor line of gimbal mounted geophones, was used for each of the techniques. Two perpendicular seismic lines were set up in the field for testing two geophone spacings. Three processing procedures, one each for the seismic reflection, P-wave tomography and spectral analysis of surface waves, were developed for producing seismic images from the P-wave reflectivity, the first P-wave arrivals and the dispersion of Rayleigh waves, respectively. The images show good complementarity in terms of investigation depth. The results are also in good agreement with available borehole data: the sandy layers seem to be related to low velocities, since the high velocities are better explained by the presence of clayey and gravelly intervals. The contribution and the limits of this seismic multi-approach method is discussed. 相似文献
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In this paper, we review the differences between velocity geophones （VG） and acceleration geophones （AG） and their effect on seismic signals acquired in onshore-offshore transition areas. We present a new generation of Land Piezoelectric Geophone （LPG） and analyze its performance. Our field experiments demonstrate that our new LPG can be used to substitute for VGs in order to eliminate phase, frequency and energy differences between different geophone systems commonlv used in transition areas. 相似文献
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采用间接边界元法（IBEM）,对Rayleigh波入射下两邻近山体的地震响应进行了定量分析。结果表明:与单个山体在Rayleigh波入射下的地震响应相比,两山地形的地震反应规律更为复杂,反应特征受控于入射波频率和山体间距等因素。总体上看:入射Rayleigh波频率较低时,两山间距对双山地形地震反应影响较大。低频波入射,受邻近山体影响,迎波面山体水平位移峰值约为入射波水平位移的6.3倍,放大效应可达单山作用的1.5倍。且山体山脚处竖向位移的频谱振荡更为剧烈,特定频率下山脚的竖向位移反应可达单山放大效应的1.6倍。较高频波入射时,迎波面一侧山体受邻近山体影响较小,且对波表现出明显的屏障效应,背波面山体地震反应强度被削弱。 相似文献
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Imaging shallow structure with active-source surface wave signal recorded by distributed acoustic sensing arrays 
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下载免费PDF全文 Zhenghong Song Xiangfang Zeng Clifford H. Thurber Hebert F. Wang Dante Fratta 《地震科学（英文版）》2018,31(4):208-214
Distributed acoustic sensing (DAS) is one recently developed seismic acquisition technique that is based on fiber-optic sensing. DAS provides dense spatial spacing that is useful to image shallow structure with surface waves. To test the feasibility of DAS in shallow structure imaging, the PoroTomo team conducted a DAS experiment with the vibroseis truck T-Rex in Brady’s Hot Springs, Nevada, USA. The Rayleigh waves excited by the vertical mode of the vibroseis truck were analyzed with the Multichannel Analysis of Surface Waves (MASW) method. Phase velocities between 5 and 20 Hz were successfully extracted for one segment of cable and were employed to build a shear-wave velocity model for the top 50 meters. The dispersion curves obtained with DAS agree well with the ones extracted from co-located geophones data and from the passive source Noise Correlation Functions (NCF). Comparing to the co-located geophone array, the higher sensor density that DAS arrays provides help reducing aliasing in dispersion analysis, and separating different surface wave modes. This study demonstrates the feasibility and advantage of DAS in imaging shallow structure with surface waves. 相似文献