Comparative Analysis of Application of Seismic Wave Reflection Method in Advanced Geological Prediction

Seismic wave reflection method is an advanced geophysical detection method in tunnel geological prediction.It is more sensitive and effective in detecting geological anomalies such as fault fracture zone and karst.In order to verify the prediction efficacy and accuracy of the seismic wave reflection method with different instruments and equipment(tunnel geological prediction[TGP]/tunnel seismic prediction[TSP])and different vibration modes(hammering,explosives),a comparison test was carried out in Jinping Tunnel.The test results showed that the time-consumption of the hammering source was short,which can greatly reduce the impact on the construction site;different vibration sources methods of seismic wave reflection can predict the unfavorable geological sections accurately.

Impact of surface-reflected seismic waves on the seismic isolation performance of circular tunnel isolation layers

Seismic isolation is an effective strategy to mitigate the risk of seismic damage in tunnels.However,the impact of surface-reflected seismic waves on the effectiveness of tunnel isolation layers remains under explored.In this study,we employ the wave function expansion method to provide analytical solutions for the dynamic responses of linings in an elastic half-space and an infinite elastic space.By comparing the results of the two models,we investigate the seismic isolation effect of tunnel isolation layers induced by reflected seismic waves.Our findings reveal significant differences in the dynamic responses of the lining in the elastic half-space and the infinitely elastic space.Specifically,the dynamic stress concentration factor(DSCF)of the lining in the elastic half-space exhibits periodic fluctuations,influenced by the incident wave frequency and tunnel depth,while the DSCF in the infinitely elastic space remain stable.Overall,the seismic isolation application of the tunnel isolation layer is found to be less affected by surface-reflected seismic waves.Our results provide valuable insights for the design and assessment of the seismic isolation effect of tunnel isolation layers.

Effective wave identification and interference analysis of the seismic reflection method in mines

Through discussion of the time-distance curve characteristics of the direct waveand from the front,side and rear of the reflection waves of the seismic reflection methodfor advanced exploration in mines,and analysis of several major interference waves inmines,the differences in time-distance curve,frequency,apparent velocity between theeffective wave and interference wave in the seismic reflection method for advanced explorationare obtained.According to the differences,the effective wave is extracted andthe interference wave is filtered and the system's precision and accuracy is improved.

2-D Seismic Reflection Method Using Iso Velocity Method of Mianwali Area

A seismic reflection of Line 12-B belonging to Mianwali Re-entrant was acquired and processed for 2-D interpretation. The line orients itself NNE-SSW direction. The sections have the shot points from VP-199 to VP-1044. Eleven Reflectors R1, R2, R3, Base Miocene, Pinchout P1, P2, P3, P4, P5P6 (Pinchout) are marked and a basement has been marked and interpreted. All the reflectors above the basement show a downward bending at the center. The depth of each reflector was calculated by iso velocity contour map method. The depth section obtained by this method shows stratigraphic features like Pinchouts. The reflectors are then correlated with the subsurface structures and stratigraphy of the area.

Application of the Common Offset Seismic Reflection Method to Urban Active Fault Surveys

The method and principle of common offset seismic surveys as well as the field data gathering and processing technique were introduced briefly. Through two urban active fault survey examples in Fuzhou and Shenyang, the efficiency and limitation of using the common offset seismic reflection technique to carry out urban active fault surveys were probed. The results show that this technique has the properties of high resolving power, better reconstruction of subsurface structures, and real-time analyzing and interpretation of investigation results on site. This method can be used to quickly locate objects under investigation accurately in the areas with thinner Quaternary overburdens and strong bedrock interface fluctuations.

A joint absorbing boundary for the multiple-relaxation-time lattice Boltzmann method in seismic acoustic wavefield modeling

Conventional seismic wave forward simulation generally uses mathematical means to solve the macroscopic wave equation,and then obtains the corresponding seismic wavefield.Usually,when the subsurface structure is finely constructed and the continuity of media is poor,this strategy is difficult to meet the requirements of accurate wavefield calculation.This paper uses the multiple-relaxation-time lattice Boltzmann method(MRT-LBM)to conduct the seismic acoustic wavefield simulation and verify its computational accuracy.To cope with the problem of severe reflections at the truncated boundaries,we analogize the viscous absorbing boundary and perfectly matched layer(PML)absorbing boundary based on the single-relaxation-time lattice Boltzmann(SRT-LB)equation to the MRT-LB equation,and further,propose a joint absorbing boundary through comparative analysis.We give the specific forms of the modified MRT-LB equation loaded with the joint absorbing boundary in the two-dimensional(2D)and three-dimensional(3D)cases,respectively.Then,we verify the effects of this absorbing boundary scheme on a 2D homogeneous model,2D modified British Petroleum(BP)gas-cloud model,and 3D homogeneous model,respectively.The results reveal that by comparing with the viscous absorbing boundary and PML absorbing boundary,the joint absorbing boundary has the best absorption performance,although it is a little bit complicated.Therefore,this joint absorbing boundary better solves the problem of truncated boundary reflections of MRT-LBM in simulating seismic acoustic wavefields,which is pivotal to its wide application in the field of exploration seismology.

Performing High Resolution Seismic Reflection for Mapping Bauxite Layers

The seismic method is able to produce highly accurate images of the Earth's subsurface. Having such detail is not only an important factor in mining, but also in civil engineering. Bauxite exploration attracts both government and industrialists to invest in it because of the high percentage of aluminum present. The economic importance of extracting aluminum from bauxite encouraged us to take this challenge;to image bauxite layers by using a high-resolution seismic reflection method at Al Qassim, Saudi Arabia. Since the subsurface structure of the area is complex, this high-resolution reflection method was carried out along a 2D line with geophone and source interval, with settings at 5 m. The result for the seismic section shows that the depth and thickness of the bauxite layer varied from 20 to 34 m, and 3 to 7 m respectively. In addition, the bauxite layer was sandwiched between clay layers. In order to achieve an even more precise depth than presented by seismic section alone, we tied the drilled wells to the seismic data and we accomplished a well match with an approximation error of 1 - 2 m, which may have been caused by the upper clay layer or by very shallow loose subsurface material. The seismic method thus applied shows the ability to detect significant details within the near surface of the earth, and considers more cost-effective than only drilled wells.

Exploring the Wenchuan earthquake fault through the accurate location of WFSD-4#Well using seismic reflection

Deep drilling data on seismogenic faults that are obtained directly can help in understanding earthquake mechanisms and the resulting changes in deep structure and material composition.However,geophysical data are necessary to ensure that the planned borehole accurately drills through the target faults.In this study,the deep crustal structure of the Longmenshan fault is explored to obtain seismogenic fault characteristics of the Wenchuan earthquake.A scientific drilling project,Wenchuan Earthquake Fault Scientific Drilling No.4 Borehole(WFSD-4)is proposed with a borehole designed to drill through the north section of the fault zone while penetrating as many geological bodies and target layers related to seismogenic fault slip as possible.High-precision seismic exploration is then carried out to study the deep structure of the fault zone and achieve the scientific objective of the borehole.Two high-precision deep seismic reflection lines were arranged perpendicularly to the fault zone,and data were obtained through special acquisition schemes and processing methods.Finally,the surface position and drilling depth route of WFSD-4 are determined based on the interpretation results of seismic profiles.The seismic reflection method for site selection of the Wenchuan earthquake fault scientific drilling is proven feasible by comparing the interpretation with the actual drilling results,laying the foundation for further study on the deep structures of fault zones.

Techniques for Surveying Urban Active Faults by Seismic Methods

Using the seismic method to detect active faults directly below cities is an irreplaceable prospecting technique. The seismic method can precisely determine the fault position. Seismic method itself can hardly determine the geological age of fault. However, by considering in connection with the borehole data and the standard geological cross-section of the surveyed area, the geological age of reflected wave group can be qualitatively (or semi-quantitatively) determined from the seismic depth profile. To determine the upper terminal point of active faults directly below city, it is necessary to use the high-resolution seismic reflection technique. To effectively determine the geometric feature of deep faults, especially to determine the relation between deep and shallow fracture structures, the seismic reflection method is better than the seismic refraction method.

Joint exploration of crustal structure in Fuzhou basin and its vicinities by deep seismic reflection and high-resolution refraction as well as wide-angle reflection/refraction

The Fuzhou basin and its vicinities are located at the northern end of the southeastern coastal seismic zone of the mainland of China. By the joint explorations of high-resolution seismic refraction and wide-angle reflection/refraction as well as deep seismic reflection in the region, which is the first synthetic profile in China, its fine velocity structure and geometric structure from the ground to Moho discontinuity is obtained. The result shows that the crust is obviously layered with a thickness of about 32 km. Basically, it consists of two parts: upper crust and lower crust. The velocity of the upper crust is 5.9-6.2 km/s in which there is a 3-4-km-thick weak low-velocity layer between the depths of 10-15 km, while the velocity of the lower crust in the range of 6.3-7.2 km/s. There exists a strong velocity gradient layer about 3 km thick above the Moho discontinuity whose velocity increases from 6.5 to 7.27 km/s. There exist high-angle normal faults that are small in size and extend only in the shallow crust. These faults are the secondary developed on the hanging wall of westward dipping low-angle normal faults. Thus, their seismogenic ability is limited, however, there exists a high-angle deep fault in the crust from Changle-Zaoan fault zone to seashore fault zone. This deep fault has cut the interface between the upper and lower crusts and Moho discontinuity, and may be the deep structure to trigger destructive earthquake source in future to affect Fuzhou City. These results have advanced the detecting precision of the deep structure in the southeastern coastal seismic zone of the mainland of China. In the aspect of the combined feature of the deep and shallow extensional structures that consist of the westward dipping low-angle normal faults and secondary normal faults on their hanging walls in the upper crust, it is firstly obtained that a united structural interpretation has deepened the knowledge about the deep dynamic process in the southeastern coastal seismic zone. At the same time, in synthetic application of deep seismic detecting methods for deep tectonic background, it possesses a wide referenced meaning to the other regions.

反射波法隧道超前地质预报地震波走时模拟研究

隧道施工安全常常由于复杂的地质情况面临着巨大的挑战,反射波法地震勘探具有探测深度大、抗干扰能力强等优点,是确保隧道施工安全的重要超前地质预报手段。反射地震波走时计算与地震数据处理中的纵横波分离、速度建模、偏移成像等多个步骤息息相关,直接影响着隧道地质预报的结果。本文将仿照反射波法隧道超前地质预报的实际施工区域进行速度建模,以求解程函方程为基础,结合快速推进法(FMM)中的迎风有限差分方法以及窄带扩展技术实现针对隧道模型的初至地震波走时模拟。并通过对隧道模型中反射界面位置信息的提取,构建反射波初始窄带以及结合窄带扩展技术实现针对隧道模型反射波走时的计算。通过数值分析以及复杂隧道模型计算表明,文中给出的反射波法隧道超前地质预报地震波走时模拟具有良好的计算精度以及较强的适应能力。

瞬变电磁法和地震反射波法在不良地质洞段超前地质预报中的应用

物探方法是超前地质预报的主要手段,通过不良地质体与围岩物性参数差异,及时发现和预测地质条件的变化。较完整一完整围岩岩体物性参数与不良地质体物性参数存在较明显差异,有利于分辨出不良地质体;但是在地质条件差洞段的不良地质体与围岩岩体物性参数差异极小,不利于分辨出不良地质体,使得岩体质量情况和地质灾害风险预报难度极大。本次采用瞬变电磁法与地震反射波法的综合物探法,在滇中引水工程大理Ⅱ段Ⅴ_(特)类岩体开展专项超前地质预报工作,主要利用岩体视电阻率、应力梯度、纵波波速、横波波速等参数对未开挖段岩体质量和可能存在的地质灾害风险进行预测。创造性地通过“日进尺”这一指标间接对开挖岩体破碎程度进行评价,经对比,预报成果中符合长度占实际开挖过程中问题段长度的85.1%,预报结果与开挖成果较为吻合;此外,对坍塌失稳段、突泥涌水段也有明显反映,为该方法组合在不良地质洞段超前地质预报中的应用提供了借鉴。

浅层地震反射波法及地质雷达法在地下防空洞探测的应用研究

由于早期人防工程相关资料的缺失,形成若干盲区。本文采用浅层地震反射波法及地质雷达法对浙江宁波地区的地下防空洞盲区进行定位探测,分析其满水和抽水后状态下进行无损检测的可行性。结果表明,结合两种方法的应用可基本实现对防空洞埋深定位探测,抽干水后状态下的反射信号更为清晰。在现场勘测应用时,应减少环境干扰,优选测试分析参数并验证结果。

槽波地震勘探技术在煤层地质探测中的应用

为准确掌握煤矿工作面内隐伏的中小型断层发育等地质情况,将槽波地震透射技术和槽波地震反射技术综合应用于文家坡煤矿4106工作面进行地质条件探测。通过波场和速度分析、频谱分析、频散分析,确定文家坡煤矿4106工作面内槽波的有效频段以及噪声频段;为宽频带通滤波提供可靠依据,进行宽频带通滤波后,分别进行透射能量CT成像和反射叠加成像;根据成像结果综合解释,将透射能量CT成像解释结果和反射叠加成像结果相互印证,确定文家坡煤矿4106工作面存在2个异常区、2条断层,为该工作面的安全生产作业提供了地质依据。

纵、横波地震反射法在断裂勘察中的综合应用

目前对城市隐伏断层的勘察精度要求日益增高,而在隐伏断层覆盖层较厚、上断点较浅的工区,单独采用纵波反射法难以实现对上断点的准确刻画。本文以工程实践为例,结合横波反射法在高精度浅层地震勘察中的优势,采用纵、横波地震反射法联合勘探实现高精度断裂勘察。实际应用结果表明:先通过地震纵波反射法,查明基岩以上的层位分布,以及较大规模断点的位置,再通过地震横波反射法,更精确地查明浅部覆盖层的层位特征以及浅部更小规模的断裂,是取得高分辨率浅层地震勘察的有效途径。

三维地震反射波勘探方法在煤田地质勘查中的应用研究——以内蒙古某煤矿电厂拟建区为例

在煤矿基本建设和生产过程中,开展详细地质勘探以查明矿井地质条件必不可少,而三维地震勘探技术是一种非常有效的手段,能够解决其他方法不能解决的地质问题。本文通过精细化三维反射波法地震勘查技术在内蒙古某煤矿电厂拟建区域的应用研究,查明了矿区目的煤层的底板起伏形态,以及地质构造、采空区、地质异常体等的分布特征,取得了良好的勘查效果,为电厂扩建提供了重要的技术支撑。

不同超前地质预报方法在岩溶隧道中的综合应用

该研究以当阳至远安铁路毛家坡隧道和槐树店隧道为对象,开展了地震波法和地质雷达法的综合应用工作。结果表明,对于毛家坡隧道,地震波法和地质雷达法的溶洞位置预报精度分别为87.18%和92.31%;对于槐树店隧道,两种方法的溶洞位置预报精度则分别为92.00%和90.32%,且地质雷达法对溶洞规模的预报精度达到了91.43%。因此,相比于单一的物探法,综合应用地震波法和地质雷达法可提高对不良地质体位置和规模的预报精度。

槽波超前探技术在彬长矿区中的应用

彬长矿区位于陇东黄土塬区,地表条件复杂且煤层埋深较深,影响三维地震勘探法探测煤层构造(断层)的精度,平面摆动误差较大。为了弥补探测精度的不足,进一步掌握断层的发育位置,科学指导矿井巷道安全、高效的掘进,在胡家河煤矿某工作面采用槽波地震超前探技术对该工作面巷道前方断层发育情况进行探测及分析。经过数据整理、反射波提取、速度建模分析和深度偏移处理技术获得巷道迎头前方的地震反射偏移剖面。实践表明,槽波地震超前探能够对断层的位置进行准确解释,通过再次对三维地震勘探资料进行分析,大大提高了解释的精度,对三维地震勘探是一个很好的补充,也为矿方后续工作提供可靠的地质依据。

地震反射波法在潼关县地热资源勘查中的应用

陕西省潼关地区北部属于深部地热资源勘查开发的空白区,区域内无深部地球物理和钻孔资料,地下地质情况和构造情况不明。为了查明潼关县北部古城景区地热资源分布情况,使用二维地震反射波法进行勘查,查明了各个时代地层的埋深及厚度、热储层位特征和断裂构造空间分布情况。在物探勘查工作基础上,于圈定的地热有利地段布设一眼地热孔,最终成孔深度为2300 m,出水量为63.2 m^(3)/h,温度为74℃。勘探成果表明,地震反射波法在潼关地区地热资源勘查中具有较好的应用效果。

隧道超前地质预报技术及综合应用

隧道掘进过程中围岩地质条件复杂多变,单一的地质预报方法存在多解性,准确率较低。基于分析不同超前地质预报方法的适用范围,建立地质分析与物探长距离预报和短距离预报相结合的综合预报解译方法,并以某高速公路隧道超前地质预报为例,采用地质分析法、地震波反射法、电磁波反射法、瞬变电磁法进行了综合超前地质预报及工程应用。结果表明:综合超前地质预报能较准确查明掌子面前方不良地质体的分布范围及性质,可有效降低施工风险,为地质灾害处理和围岩设计变更提供依据。