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Über dieses Buch

This book focuses on essential theories, methods and techniques in the field of environmental and engineering geophysics that can contribute to resource detection and environmental protection. Geophysics has been playing an important role in exploring the earth, locating vital resources and promoting the development of society. This book covers a range of topics including the exploration of modern resources, such as ore deposits, coal mines, shale gas and geothermal power, and the monitoring of geological disasters, including the rock-soil body, ground deformation, mines, specific rock-soil engineering disasters, desertification of land and environmental abnormalities.

This book not only offers a valuable resource for geophysical researchers; it also demonstrates how geophysics theories and methods can be practically implemented to protect our environment and promote the development of human society.

Inhaltsverzeichnis

Frontmatter

Application Research of Ant-Tracking Technology Based on Spectral Decomposition in Xingdong Mine

This work in Xingdong Mine 1200 Area is focused on use of the basic documents of seismic, logging and site disclosure and the results of comprehensive geological research. Based on Petrel geological modeling platform, applying the advanced spectral decomposition and Ant-Tracking technology, taking Xingdong Mine 1200 Area as an example, the large, medium and small-scaled discrete crack network models are established. It has also made reconstruction and realized the effective prediction of the fault system and Collapse-column, which provided a solid fundamental guarantee for the prediction of faults and complex geological body in other regions.

Jiangong Liu, Yanhui Wu, Peng Wang, Jia Song, Gouju Wang, Wentao Ma, Wei Wang

Definition and Improved Algorithm of All-Time TEM Apparent Resistivity

An improved TEM all-time apparent resistivity is proposed. Firstly, we give its definition. Its definition at time t(i) is the comprehensive resistivity of the zone from Depth(i − 1) to infinity, where, Depth(i − 1) is the maximum TEM field diffusion distance at time t(i − 1). Then, we give its algorithm based on the binary search algorithm. Finally, a half-space model and a whole-space model are constructed to test the proposed method. The traditional all-time apparent resistivity and the improved all-time apparent resistivity are calculated respectively by using the models built above. The results show that compared with traditional method, the improved all-time apparent resistivity is more fit to the theatrical model, and have higher precision and resolution.

Fei Li, Shangxian Yin, Demin Liu, Yong Han, Shuai Hua, Peng Chen

The Fast Imaging of Metal Pipe Exploration Using TEM Method

The transient electromagnetic is one of the important geophysical methods, widely used in various fields, but there exist some problems when solving engineering geophysical problems. In response to this shortcoming, several methods are proposed for TEM imaging (dynamic multi-channel curves, Dynamic induced electromotive force contrast curve, dynamic apparent resistivity and dynamic resistivity depth map) to solve the problem of detecting at the scene quickly finding horizontal location and depth of metal pipe and other engineering problem in cities. And TEM has a relatively deep depth compared with metal pipe instrument and get more information about the features of subsurface. Finally, transient electromagnetic method proved quick detection the metal pipe problem through the detection experiments and several dynamic imaging method of metal tube.

Zhaoqiao Zhang, Shucai Liu, Yong Zhang, Longjin Zheng, Lian Liu

Absorbing Quality Factor Attribute for Recognising Ordovician Cave and Underground River System in Tahe Oilfield

At Tahe Oilfield Ordovician strata, caves and underground rivers are the commonly developed geological structures…. Caves and underground rivers serve as connection pipes for different types of reservoirs, and are also an important part of a reservoir. This paper presents the researched carried out on a block of high resolution 3D seismic data from Tahe oil field. For the research, Absorption quality factor attribute (AQF) was tested with the aim of identifying the cave and underground river systems. In the AQF attribute sections, the caves were depicted clearly and some inconspicuous dot-like seismic reflection and some seismic reflection troughs were better displayed. In addition, the original seismic, similarity attribute data, body sculpting technology and drilling data successfully verified the caves which were predicted from the AQF data. Our research shows that AQF attribute identifies the caves and underground river systems very well. Hence, AQF attribute is useful in identifying and dividing caves and underground river systems.

Yuxin Luo, Ruizhao Yang, Pengpeng Li, Duo Gao, Chao Liu

Research on Induced Polarization Relaxation Properties of Sand Sample

The work discuss the main influencing factors of induced polarization effect including porosity, water content and current intensity from the analysis of induced polarization relaxation properties. The experimental device of induced polarization four-electrode method has been used to contrast three groups (particle size 0.6–1.18, 1.0–1.4, 2.36–4.72 mm) of aquifers sand sample. Different current has been supplied into each particle size group of sand simple with different water content (2–24%) to explore the impact of the relationship between aquifers sand sample and the induced polarization relaxation properties.

Qian Guo, Lichao Nie, Shucai Li, Bin Liu, Chuanwu Wang, Mingzhen Tian

The Trust Region Method for Time-Domain Full Waveform Inversion

Full waveform inversion is an effective inversion method to obtain high resolution and precision seismic imaging. The problem of full waveform inversion aims to solve the optimization problem of the misfit between the synthetic and recorded data. There are a lot of conventional local optimization methods, such as the methods depending on gradient and Hessian matrix, to solve the ill-posed nonlinear problem. Gradient and Hessian matrix information plays an important role in inversion algorithms. However, these methods always lead to local minimum so that the result of inversion could not be accepted. To confront the problem, we propose a new approach called the trust region method, to solve the unconstrained optimization problem. Strong convergence properties are the key for trust region method, and the new step is limited to the neighbourhood of the current step. The gradient and Hessian matrix information has an effect on inversion algorithms. To test the capability of this method, we apply it to the model of salt domes and synthetic Marmousi from the time-domain acoustic full waveform inversion point of view for reconstructing velocity model. Inversion results show that the model inverted by our method fits the true model well and the precision is high. Hence, the trust region method is a promising method for the problem of full waveform inversion.

Suping Peng, Peng Lin, Wenfeng Du, Yongxu Lu

Research on the Channel Wave Field Characters of Goaf in Coal Mine and Its Application

Goaf badly affects coal mine production safety; therefore, accurate geophysical exploration method to ascertain the goaf is urgently needed. Channel wave seismic technology is suitable for coal mine goaf detection because it has many advantages, such as long transmission distance, high resolution. Because coal seam thickness affects the wave propagation, firstly, we carry out numerical simulation under the condition of coal seam thickness variation in the goaf. Secondly, we analyze the channel wave field characteristics of the goaf. Thirdly, we pick up the dispersion curve of transmitted channel wave. Lastly, we discuss the effects goaf makes on channel wave and imaging condition under the variation of the coal thickness. The results show that, the Airy-phase velocity of channel wave decreased as thickness of coal seam increases, and the dispersion strengthens as Wave propagation distance becomes longer. Firstly, seismic reflection survey is carried out in the target area: 15,030 working face of Xin’an coal mine. Through the analysis of dispersion, spectrum, direct wave’s velocity and travel time of the shot-gather records, we recognize the reflected waves from the goaf. The goaf boundary is imaged by the Kirchhoff migration method. Combining the other results of geophysical exploration with the known geological data we geologically explain the imaged results.

Feng Lei, Wei Wang, Songying Li, Xiaoshuai Yao, Jiwen Teng, Xing Gao

The Study of Well Logging Sedimentary Microfacies in Tengge’er Formation Baiyinchagan Depression

Through analyzing the corresponding relationship between the log characteristics parameters and sedimentary microfacies, the electrofacies mode of Tengge’er Formation Baiyinchagan Depression is established based on the regional sedimentary background, the rock characteristics and its electrical response characteristics and the extraction of logs curve amplitude and the characteristic’s parameters which can reflect sedimentary microfacies. The results show that the southern ramp of Tengge’er Formation in the Baiyinchagan Depression takes the braided delta facie as the major style, and it can be further divided into 7 sedimentary microfacies, including upperwater distributary channel, flood plain, underwater distributary channel, interdistributary bay, mouth bar, frontal sheet sand and frontal wedge-shaped sand. The divisions of sedimentary system and sedimentary facies are perfected through analyzing the logging microfacies, sedimentary and sequence stratigraphy characteristics of single well, which can provide an effective basis for the further exploration of oil and gas in this area.

Xinhu Li, Qiuling Wang, Wenhui Ma

Improvement on AVO Equations in VTI Media

In weakly anisotropic VTI media, it is assumed that the ray directions of phase and group velocities are consistent, and P wave excites the horizontal interface, we take into account the equations between the anisotropic angle and the isotropic angle with the same horizontal slowness, and re-deduce AVO equations for VTI media again. The new equation shows that it has no effect on AVO equation for P wave, but improves AVO equation for SV wave.

Xiaoting Li, Hongwei Wang, Suping Peng, Wenfeng Du, Yingchuan Sun

Determination of the Conversion Point for P-SV Wave of Horizontal Interface Under Rugged Surface

P-SV wave requires accurate conversion point to get common conversion point collection. However, there is no method to get exact conversion point under rugged surface. This paper established an iterative equation to get the exact conversion point under the rugged surface, and proved effectiveness and accuracy of the iterative equation.

Liang Sun, Suping Peng, Dengke He, Chao Sun

The Study of Anti-noise Immunity for Electromagnetic Method Based on m Pseudo-random Sequence

Electromagnetic methods play an important role in the exploration of metal ore mineral, oil and gas resources. It is very difficult to obtain a high signal to noise ratio with increasingly electromagnetic noise using conventional anti-noise method. In recent years, the pseudo random sequence attracts a lot of attention because of its anti-noise performance. This paper describes two common methods used to extract the impulse response from the pseudo-random sequence response studies have shown that the two methods are available to get high-precision impulse response without noise.The extraction accuracy of the results using the two methods were compared with date contained in the noise, that shows that the results of method 2 is better than 1, then analyzing the reasons for this situation. Finally, the study is made to improve the ability of the anti-pseudo-random sequence of methods, including to improve the order of the pseudo-random sequence, using a different encoding, change the number of cycles in order to achieve the purpose of noise suppression.

Xianxiang Wang, Juzhi Deng

Pit-Surface Electromagnetic Receiver

The purpose of a multi-parameter observation system for pit-surface is to achieve high-accuracy observations via electromagnetic signals in tunnels and on surface. The existing ground electromagnetic observation systems have high background noise with low field applicability. The existing non-polarized electrode and inductive magnetic sensors are difficult to operate in tunnels. To solve the problems, an electromagnetic observation system with chopper amplifier circuits for pit-surface has been developed. According to the non-contact electrode principle in the medical field, a non-contact electrode was developed for electric field observation to solve the difficulty of connecting tunnels to ground surface. A 3-axis audio magnetic sensor was developed to solve the existing problem of poor adaptability of large inductive magnetic sensors in narrow tunnels. In the meantime, a number of good improvements for field applicability have been made for the observation system, which greatly enhanced the efficiency of field operation. A series of indoor and field tests were performed, and results confirmed the validity and advancement of the multi-parameter electromagnetic observation system for pit-surface.

Kai Chen, Haifeng Wang, Ming Deng, Hong Chen, Di Zeng, ShuangChao Ge

Three-Dimensional Resistivity and Induced Polarization Data Inversion with Image Focusing

A maximum smoothness stabilizing functional constraint is normally used to stabilize the three-dimensional (3D) direct current (DC) resistivity and induce polarization (IP) data inversions process. These kinds of algorithms can converge stably, but the obtained solution is a smooth image, which in many practical situations does not describe the examined object properly. In this paper, we present a regularized inversion with image focusing of 3D DC resistivity and IP data. In the inversion approach, the minimum support functional constraint is incorporated into the objective functional, then the damped Gauss-Newton method is used to find the optimization of the objective function, and the preconditioned conjugate gradient algorithm is used to calculate the model updates. The model tests show that the proposed inversion approach owns good reliability and stability. The comparisons show that the program helps to generate more focused and resolved images of blocky geoelectrical structures and with better convergence than the traditional smoothing inversion approach.

Yixin Ye, Zhiyong Zhang, Zelin Li, Yong Zhao

A Study of the Southern Segment of the Greater Khingan Range Mineralization Belt, China, Based on the 3D Parallel Inversion of Potential Data

In this paper, a geophysical interpretation of the southern segment of the Greater Khingan Range mineralization belt is firstly introduced. The conventional analytic methods (e.g. continuation) are implemented to illustrate the source of the regional anomalies. Also, we use a new massively parallel inversion code to provide a high-resolution 3D imaging of density and magnetic susceptibility of the whole studying area. The deposit-scale 3D susceptibility inversion models of Dajing and Huanggang are compared and discussed as typical mineral deposits model. The result offers an intuitive overview of geophysical properties and shows a high agreement with the geology settings.

Wuyang Li, Jian Zhang, Daeung Yoon, Wei Lin

A Fast Topographic Correction Method for TEM Data

Topography affects electromagnetic data and leads to wrong interpretation of shallow resistivity layers. In this paper, we propose a new method for correcting topographic error in electromagnetic data. In order to achieve this, we used a small DC configuration to obtain the surface resistivity, and then used the surface resistivity to construct a new topographic correction formula. Both synthetic and field TEM and CSAMT data were processed using this method. The results show that our method is a fast, effective and practical tool for correcting topographic effects in electromagnetic data.

Guoqiang Xue, Weiying Chen, Jiangwei Cui, Shu Yan

Distinguishing Multi-layer Mined-Out Area Through TEM

Loop TEM has over the years played important role in detecting single water-filled goaf. In order to exploit deep coal beds, the investigation of multi-layer aquifer became an important new task for coalfield hydro-geophysical prospecting using TEM. Because it has become necessary to modify the traditional interpretation technology. In this paper, based on the numerical calculation of typical horizontal layered earth model, the feasibility of probing multi-layer aquifers was analyzed. Secondly, while fitting inversion to TEM sounding curves, the number of layers was supposed to be equal to the number of time channel. Multi-layer aquifers were detected using central loop TEM in Shanxi Province. The exploration result has been validated by borehole drilling. This study shows that it is feasible to detect multi-layer aquifers with central loop TEM technique.

Shu Yan, Guoqiang Xue, Weizhong Qiu

Bias in Transient Electromagnetic Method Due to Non-rectangular Loop

Rectangular loop is one of the most popular transient electromagnetic (TEM) devices, which is widely used in engineering, hydro-geological and ore deposit exploration. However, in theory, circular loop is used to approximately simulate the rectangular loop. Traditionally, this gives rise to a series of problems. Meanwhile, in practice, the rectangular loop is not easy to layout on field especially in complex terrains or mountainous areas. Therefore, we have modified the rectangular loop. The geometry of the loop may now be arbitrarily named, modified-rectangular loop. However, some bias will be caused if standard rectangular-loop parameters are used to invert the field data from modified rectangular loop. And this bias lowers the detection precision of the modified rectangular loop. Therefore, the bias caused by the approximation of circular and modified rectangular loop is analyzed in this paper. Firstly, the response distribution and bias between circular loop and rectangular loop are compared using induced voltage and primary field. Then, the forward method of vertical magnetic field from modified rectangular loop based on coordinate transformation is given. The bias between rectangular loop and modified rectangular loop are then analyzed using vertical magnetic field. From theoretical modeling that there is an indication that changing the loop geometry will result in some error and lower the detection precision.

Nannan Zhou, Guoqiang Xue, Dongyang Hou, Huasen Zhong, Hai Li, Jiangwei Cui, Kang Chen

The Shielding Effect of Low Resistivity Layer in TEM

Transient electromagnetic method can penetrate high-resistivity shielding layer and delineate underlying strata or structure. However, the shielding effects of low-resistivity layer on transient electromagnetic exploration are often ignored, especially for low-resistive overburden. It is of great importance to ensure exploration depth and improve detection precision by researching the relationship between low-resistive layer and electromagnetic field. In this paper, the propagation process of the subsurface and surface TEM field responses were simulated using finite-difference time-domain method (FDTD). And the characteristic response of low-resistivity overburden was studied using numerical modeling. The observation time with low-resistivity layer was estimated using observation time formula. It was shown that a low-resistivity layer will not only reduce the propagation speed of the field, but also weaken the response of low-resistivity target.

Dongyang Hou, Guoqiang Xue, Nannan Zhou, Shu Yan

Research Progress in High Power Multi-functional Borehole-Ground Electromagnetic Transmitter for Metal Exploration

Enhancement of transmitting power is an effective way to improve the depth of electrical prospecting. The objective of this method is to provide adequate offset observation in order to minimize source field effect and to reach a deeper depth of exploration. In addition, placement of electrically excited field source underground close to the exploration object and underground is a new prospecting technology in metal exploration. This method is implemented using existing pit, mine or borehole with the purpose of obtaining stronger and improved information on both the exploration depth and the definition of the anomalous body. Therefore, we have developed a transmitter that can be used as the excitation device for artificial electromagnetic source. It uses a type of large power inverse rectangular wave that works in an automatic sweep manner, the frequency of the transmitter signal range between 10 and 0.01 Hz, the maximum transmitter power is 48 KW, the maximum transmitter current is 60 A, it can realize the on-time planned power supply transmitting with the GPS clock and real time clock (RTC), and also record the information of several auxiliary status. We have been able to certify through experiments that the performance of the device is reliable and stable. And that the device can satisfy the demand for electromagnetic prospecting of metal mining, prospecting for deep and concealed ore bodies and the exploration of sustainable resources for solving resource mining crisis.

Meng Wang, Sheng Jin, Ming Deng, Bo Wang, Zheng Xiang, Ziheng Zhao

Research on Investigation Characteristic of Multicomponent Induction Logging in Mineral Logging

We introduce the multicomponent induction logging method to model mineral deposit of limited distribution in order to realize fine evaluation of the solid mineral deposit. In this study, the azimuthal and radial detection characteristics of the components were studied using numerical simulation. The results show that XZ- and ZX-components have the farthest depth of investigation and also exhibits azimuthal sensitivity, which could be used to determine the relative position between an ore body and borehole.

Jian Wang, Hao Chen, Xiuming Wang

The Extraction of TEM Response from Pseudo Random Binary Sequence Source EM Data

This paper presents a method for converting the full waveform electromagnetic response excited by the pseudo-random binary sequences (PRBS) into subsurface resistivity cross section, based on the recovery of the transient electromagnetic diffusion field. The impulse response of the earth is extracted from the full waveform data efficiently using the Wiener-Hopf equation. Then, the backward accumulation is used to obtain the step off response from the extracted earth impulse response. An OCCAM inversion routine, which incorporates the band limitation of the derived transient, is adopted to produce the geoelectric models. Finally, the method was applied to the experimental field data set, and the consistency between the recovered models and the geological condition verifies the validity of this method.

Hai Li, Guoqiang Xue, Pan Zhao, Huasen Zhong, Nannan Zhou

Application of Ant Tracking Technique in Fault Interpretation of YC Coal Mine

In coalfield seismic exploration study, the general interpretation is based on the observation and identification of the characteristics of seismic section. The space distribution of the fracture system can be well demonstrated by an advanced automatic tracking method, the ant tracking technique. Due to the limitations on the manual interpretation technique, it can only identify the fault and fracture that are evident. The automatic interpretation results obtained from the ant tracking technology, when compared with manual interpretation result, was more clearer, intuitive and accurate. It was considered that the technique has good application value in the interpretation of coalfield structures.

Dongyang Liu, Suzhen Shi, Wenfeng Du, Tailang Zhao

Earthquake Detection with Seismic Exploration Method

Seismic exploration technology has been widely used in petroleum exploration and engineering fields, but it has received little attention for the study of structural changes and detection after earthquake. In this paper, at first we analyzed the data obtained in 2008 from trenches, coring, well logging and geophysical exploration after/during the Wenchuan Ms8.0 earthquake. The results show that the Wenchuan earthquake was formed by cryptoexplosion process which was gradually triggered from the southwest to the northeast. The energy of cryptoexplosion includes two aspects, one of which is underground supercritical fluid phase explosion, and the second is discharge lightning of underground negative charge accumulation. From seismic section, we identified the characteristics of underground changes caused by cryptoexplosion. Lastly, seismic exploration carried out in the Japan South Sea was further compared and it also has underground cryptoexplosion characteristics. This means that genetic mechanism of earthquake is not mainly caused by structural movement but mainly by underground explosion. These results show that seismic exploration is very effective in identifying the underground explosion characteristics caused by earthquake.

Guanghe Liang

Lamellate Layer Convergence Algorithm Based on the Magnetotelluric Equivalence Principle

The non-uniqueness problem of inversion is a large obstacle in improving geophysical interpretation resolution. At present, the main factors which affect the non-uniqueness of the solutions of magnetotelluric sounding are equivalence and volume effect. For example, true parameters of low resistance lamellate layer are difficult to determine by inversion because of the ‘s’ equivalence, and we usually get the biased thickness and resistivity that meets equivalence condition, which is clearly not consistent with the actual situation. In order to make the inversion results correspond to the actual situation better, the new assistant algorithm based on the Marquardt inversion and equivalence principle was designed in this paper, and we used ‘S’ and ‘H’ equivalence principle flexibly to make the thickness and resistivity converge to a result that is more close to the actual situation. This method provides a convenient means of combining magnetotelluric sounding data with logging and seismology data to make associated interpretation or inversion, so that thickness and resistivity of target can be determined effectively.

Rongjiang Tang, Xuben Wang, Lu Gan, Juntao Zhang

Discussions on Resolution of Different TDEM Survey Techniques for Detecting Water-Bearing Structures

It is common when using TDEM to measure only inside the transmitter loop. In groundwater and environmental applications, this is almost ubiquitous. This situation arose because inversion applications were available only for central loop readings (Anderson in Improved digital filters for evaluating Fourier and Hankel transform integrals, 1975 [1]) and geoscientists thought of such readings as soundings similar to resistivity sounding applications. But, should we consider TDEM data as analogous to reflection data and measure proximate to the source or as analogous to refraction data and measure away from the source? In mining applications, three-dimensional modeling has long been available and the use of multiple measurements inside and outside loops has been common for three decades. In this paper, we examine several misunderstandings and problems associated with in loop approaches by comparing results from different TDEM survey techniques. We utilize both synthetic and field data for our studies. Both synthetic and field data indicates that the use of in loop data is potentially dangerous, as this location is poor for sensing resistive structure. In addition, single station inversion is limited without considerable knowledge of the geology within the study area, as 1D inversion is highly non-unique. The use of multiple data in a 1D inversion helps locate the correct model subspace and it appears that out-of-loop data has fewer possible models. Fixed loop surveys can provide more accurate deep inversion results if the ground is sufficiently one-dimensional. It also provide an array for faster surveys and more area coverage.

Lei Yang, R. W. Groom

A Simple Apparent Resistivity Definition for Modified Central-Loop TEM System

Central-loop TEM technology can be used to survey the response of just central point. In practice, ones design modified central-loop TEM system to survey the response of several point around central location (within which the field is assumed to be uniform). However, there still exist some theoretical problems needed to be solved in obtaining TEM responses of this kind of modified system. In this paper, calculating and comparing the circle central-loop and modified circle-loop configuration of magnetic field responses at different non-center distances have been finished. The equations at non-center points are constructed using the technology of polynomial iteration. The polynomial coefficients are obtained adopting the method of least-squares iteration. Then, the improved calculation formula of the apparent resistivity at non-center points is constructed by adding an extra coefficient to the conventional formula, and this can make it better apply to TEM data collected at non-central locations of a circle-loop. Then the equivalent of circle and rectangular loop has been discussed; at last, the result due to circle loop has been introduced into square loop system and develop a new method to calculate the electromagnetic field response and apparent resistivity at non-central. An improved expression of apparent resistivity at non-center points is constructed and validated by a given model as well as coal water-filled area location, which shows that the constructed method is feasible.

Yunfei Lu, Guoqiang Xue, Xiu Li, Zhipeng Qi

The Response of In-loop Transient Electromagnetic Configuration

For the aim to assess the large loop transient electromagnetic method (TEM), an important method in engineering exploration, we study the distribution of vertical and horizontal magnetic component by calculating the 1-D response corresponding to in-loop and out-loop field point. A new algorithm for Dual Bessel integral has been developed. We divided the integral range $$ (0,\infty ) $$(0,∞) into $$ (0,\lambda_{0} ] $$(0,λ0] and $$ [\lambda_{0} ,\infty ) $$[λ0,∞). In the integral range of $$ (0,\lambda_{0} ] $$(0,λ0], based on the derivative relationship of Bessel integral, transforming the integral into the form of easily calculation. In the range of integral of $$ [\lambda_{0} ,\infty ) $$[λ0,∞), Linear sine and cosine transformation algorithm can be used for the computation. We design models for numerical simulation and give the result. Based on the results, we draw a conclusion that vertical magnetic field component can be surveyed in the range of 50% inside of the loop and horizontal magnetic field component is so smaller than vertical component that it can not be well surveyed inside large loop.

Wen Chen, Guoqiang Xue, Dongyang Hou

Application of Multiple Geophysical Methods to Prospect Concealed Ores Beneath Quaternary Cover: A Case Study from a Copper-Polymetallic Deposit

The magmatic hydrothermal vein-type copper-polymetallic deposits in Weilasituo are strictly controlled by NE-trending fault zones. Whether the concealed orebody exists in the north of Weilasituo ore district is an urgent problem to be solved. The northern of Weilasituo ore district was covered by Quaternary sediments, possessing similar metallogenetic conditions to Weilasituo ore district. In order to investigate the concealed oresbodies, the authors build the multiple geophysical procedures to prospect concealed orebodies in coverage area, including gravity, magnetic induced polarization in median gradient array and controlled source audio-frequency magnetotelluric measurements. Based on the results obtained above, it has been demonstrated that there exists a concealed orebody in the north of Weilasituo ore district. Multiple geophysical procedures constructed in this paper to prospect blind orebodies beneath coverage area, can meet the demand of prospecting ores in covered areas.

Yinsheng Meng, Ruizhong Zhang, Ruide Liu, Tianliang Lin, Wenguo Wang

Accurate Recognition of Underwater Riprap of Rivers and Lakes Based on the Seismic Imaging

During the operation of rivers and lakes dam, due to the reasons for engineering measures, deposition or geological disaster, bank collapse and the river changes still occur. To enhance slope stability and anti-erosion ability, reducing the incidence of bank collapse, the riprap method is widely used in revetment dam engineering. In general, such as riprap stacked body is stable when dry, but with the water level rise and changes in natural conditions, loosely stacked body will slip to the bottom of collapse, leading to reservoir sedimentation, even a threat to the dam safety. Therefore, we should track and monitor the range, chemical speciation of these stacked body periodically, on the one hand is the need for the project to evaluate the quality of underwater riprap, the other is an indispensable work for the management to ensure the flood discharge section and the capacity of the reservoir. However enrockment has loose characteristics, the body full of water and sediment, it can no longer be regarded as a single block. Furthermore earthquake method is limited by the epicenter equipment frequency band, energy size and bubble effect, it is difficult to achieve seismic wave signal by artificial excitation penetrating the underwater gravel, riprap and other discrete body, so it is difficult to collect enough seismic wave that has high signal to noise ratio to reflect the occurrence status of enrockment. Combined with the exploration of Longhekou serveroir, using a new type of source equipment called ‘a light pressure type automatic trigger device which could be used in shallow water’. The practice results showed that the distribution and thickness of riprap which seismic imaging identified was coincided to the physical truth. This provided important theories and practical basis for accurate identification of underwater target in shallow water by using the seismic imaging method.

Fuyu Jiang, Wenkai Chang, Leilei Xie

Application of Seismic Imaging Method in Detecting the Complex Geological Hazards

In recent years, geological hazards happened frequently, for example goaf, karst, ground fissure, landslide threatening engineering construction and human life severely. How to take some measures effectively and find out the space character of geological hazards are very important to control geological hazards. In this paper, we firstly explain the principle of seismic imaging method. Then analyze the character of geophysical abnormity in the different geological hazards, and discuss the effect of seismic imaging method in detecting the geological hazards. Meanwhile combining with some engineering examples, we have detected these geological hazards accurately and we can get some proofs from the borehole. It indicates that this method has lots of advantages in detecting geological hazards. For example high resolution, low cost, high efficiency and it can make up for disadvantages of other detecting methods.

Hua Zhang, Hui Yang, Luoyi Zhang

Theoretical Study on Tensor Controllable Source Electromagnetic Field Distribution Law

Tensor controllable source electromagnetic method was put forward long; however, since controllable source launching system satisfying tensor electrical impedance observation is quite complex and hard to manufacture, it was difficult to be applied. In 2010 Germany Metronix Company developed successfully the first controllable source magnetotelluric instrument that satisfied tensor electronic impedance observation, whose rotating dipole launcher could launch magnetic fields with different directions of polarization, different tensions and different frequencies. Now optimal electromagnetic field signals at all points within the testing area could be observed. That is why theoretical study was conducted on such launching device in this essay.

Ruodi Yang

An Optimization Method for Interpreting ERT Data Based on Groundwater Numerical Modeling (Which Data Polarization Mode Should Be Used in 2D Inversion)

Aiming at choice of data polarization mode in magnetotelluric 2D inversion, trying to assist the geophysical inversion with the hydraulic characteristics of the water level and water quality information contained in the geological body. Based on this idea, a method for interpreting ERT data based on groundwater numerical modeling which data polarization mode should be used in 2D inversion is provided in this article. In this article, Magneto-telluric method as a way to accomplish numerical simulation of geophysical forward and inversion. Firstly, by studying the known geological model and multiple geological models with different choice of data polarization mode interpreted from ERT data, a set of groundwater numerical models can be set up. Then numerical simulation of groundwater flow and solute transport were conducted. Lastly, the optimal data polarization mode can be obtained by comparing the result of numerical simulation of groundwater. Sensitivity analysis were also conducted to verify the method. And the result show that the inversion model using only TE mode data is more valid, next is TE + TM, TM mode only is not proposed by comparing the numerical value of Standard of the Estimate, Root Mean Squared, Normalized RMS and Correlation Coefficient.

Xuelan Li, Diquan Li, Bo Yuan, Yanhui Dong

Surveying Karst Caves Under 14 Tunnels Bottom on Gui-Guang High-Speed Railway

In order to prompt the development in west China, it is necessary to construct high-speed railway. However, there are many limestone and dolostone, as well as karst caves in west China, especially in GuiLin city, which make it difficult to dig tunnel or build bridge. A new method, (named Landsonar by authors), which use an extremely small source-geophone distance single-channel was introduced and applied for surveying karst caves in 14 tunnels among 179 km railway. Landsonar result and boreholes recorder agree with each other.

Shihang Zhong, Rong Wang, Zefeng Wang
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