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1.
Mapping of glaciotectonic deformation in an ice marginal environment with ground penetrating radar 总被引：1，自引：0，他引：1
A series of closely spaced parallel ground penetrating radar (GPR) profiles of glaciotectonic deformed glacio-fluvial sediments have been obtained in an ice marginal environment in Northwest Zealand, Denmark. The radar profiles can be differentiated into several radar facies with distinct reflection characteristics. The lithology and depositional environment of the radar facies is interpreted by correlation with information from profiles in gravel pits, geological maps and drill hole data. The radar facies include glaciotectonically disturbed glacio-fluvial sediments, sediments deposited penecontemporaneously with the deformations and sediments deposited post-tectonically. Several thrust planes with dip angles between 25° and 30° as well as major folds and minor faults have been interpreted from the GPR data. The deformation style of the deformed glacio-fluvial sediments is a thin-skinned pro-glacial thrust complex, with associated folding. The deformations have resulted in the present ridge morphology seen in the rim of the composite ridge. Syn- and post-tectonic sediments are deposited on top and in front of the deformed sediments, smoothing the ridge relief created by the thin-skinned thrust complex. A structural geological map constructed from the ground penetrating radar data reveals the extension of the individual radar facies in the thrust complex. Tectonic features such as thrust planes and folds can be followed throughout the mapped area. 相似文献
2.
Ground-penetrating radar (GPR) is used to image and characterize fall and pyroclastic flow deposits from the 1815 eruption of Tambora volcano in Indonesia. Analysis of GPR common-mid-point (CMP) data indicate that the velocity of radar in the sub-surface is 0.1 m/ns, and this is used to establish a preliminary traveltime to-depth conversion for common-offset reflection profiles. Common-offset radar profiles were collected along the edge of an erosional gully that exposed approximately 1–2 m of volcanic stratigraphy. Additional trenching at select locations in the gully exposed the contact between the pre-1815 eruption surface and overlying pyroclastic deposit from the 1815 eruption. The deepest continuous, prominent reflection is shown to correspond to the interface between pre-eruption clay-rich soil and pyroclastics that reach a maximum thickness of 4 m along our profiles. This soil surface is distinctly terraced and is interpreted as the ground surface augmented for agriculture and buildings by people from the kingdom of Tambora. The correlation of volcanic stratigraphy and radar data at this location indicates that reflections are produced by the soil-pyroclastic deposit interface and the interface between pyroclastic flows (including pyroclastic surge) and the pumice-rich fall deposits. In the thickest deposits an additional reflection marks the interface between two pyroclastic flow units. 相似文献
3.
Ground penetrating radar (GPR) survey was conducted in the Wushanting mud volcano field (Yanchao, Kaohsiung) using a 500 MHz antennae, which allowed high-resolution imaging of subsurface structures. Seven GPR reflection characteristics are recognized. Sigmoid GPR reflection patterns resulted from a recent mud lobe deposited above an underlying older mud lobe front. Contorted GPR facies resulted from recent mud flow which encountered obstacles. Subparallel reflections resulted from mud volcano deposits of limited flowability, low velocity and gentle gradient. Hummocky reflection patterns are formed by interfingering of recent mud lobes building onto low land. Disrupted GPR facies were due to lateral breaks of continuity from mud cracks, which, according to field observation, can provide channels for erosion and form deeper erosion gullies. GPR time slices of different depths are rendered as a three-dimensional model. Approximately orbicular GPR reflection characteristics can indicate arcuate stacked mud lobe fronts of different periods. Some depositional models to explain GPR reflection characteristics can be founded upon observations of recent sedimentary phenomena. The models of this study may be applied to paleoenvironments and the depositional evolution of mud volcanoes in similar geological settings. 相似文献
4.
In order to improve the reliability of the ground penetrating radar (GPR) method in identifying subsurface sinkholes and karst cavities, laboratory investigations have been performed. The main objective of this work was to examine the relationship between horizontal/vertical voids dimensions and wavelengths of various antennas, and the corresponding GPR responses. Emphasis was given to the investigation of the factors that cause the appearance of reverberation phenomena in the signal pattern.The tests were conducted in 5 m × 10 m area by 2-m-deep trench filled with homogenous, dry sand. The voids models (empty fiberglass cylinders in diameters of 0.6 m, 1.0 m, 1.5 m and 2.4 m, with various heights) were buried vertically with their tops at depths of between 0.7 and 1.5 m. Investigations were performed for the various model conditions by towing 500, 300 and 100 MHz antennas along a pre-established grid, for the various model conditions.The GPR data collected using the 500 MHz bistatic antenna above the 1.0-m- and the 1.5-m-diameter cylinders, and using the 300 MHz bistatic antenna above the 1.5-m-diameter cylinder, confirmed the presence of a reverberation phenomenon, i.e. a strong convex signal pattern, containing a series of high amplitude extending oscillations with reduced frequency.Based on past practical GPR experience of void detection and presently obtained experimental data, two rules of thumbs may be adopted for the prediction of the appearance of resonant radar pictures:
- 1. The void diameter larger than the wavelength in air of the antenna used.
- 2. The vertical size of the empty void not significantly smaller than its horizontal dimension.
5.
《Journal of Applied Geophysics》2007,61(3-4):179-200
Ground penetrating radar (GPR) survey was conducted in the Wushanting mud volcano field (Yanchao, Kaohsiung) using a 500 MHz antennae, which allowed high-resolution imaging of subsurface structures. Seven GPR reflection characteristics are recognized. Sigmoid GPR reflection patterns resulted from a recent mud lobe deposited above an underlying older mud lobe front. Contorted GPR facies resulted from recent mud flow which encountered obstacles. Subparallel reflections resulted from mud volcano deposits of limited flowability, low velocity and gentle gradient. Hummocky reflection patterns are formed by interfingering of recent mud lobes building onto low land. Disrupted GPR facies were due to lateral breaks of continuity from mud cracks, which, according to field observation, can provide channels for erosion and form deeper erosion gullies. GPR time slices of different depths are rendered as a three-dimensional model. Approximately orbicular GPR reflection characteristics can indicate arcuate stacked mud lobe fronts of different periods. Some depositional models to explain GPR reflection characteristics can be founded upon observations of recent sedimentary phenomena. The models of this study may be applied to paleoenvironments and the depositional evolution of mud volcanoes in similar geological settings. 相似文献
6.
地质雷达是利用电磁波对地下不同电性介质进行探测的地球物理仪器，其探测速率快、分辨率高，可弥补探槽和其他地球物理方法存在探测盲区的缺陷，正在越来越多地应用于活动断层探测领域。本文以乌拉山山前断裂为例开展地质雷达探测工作，使用无人机正射影像技术对测线进行地形校正，获得断层浅部地质雷达图像。研究结果表明，本文研究方法能有效反映探槽揭露的地层单元和断层分布。本次探测中，雷达波形图像特征为:浅地表的土壤层反射波总体较弱；粗粒沉积为主的砾石层反射波总体较强，同相轴连续性好；细粒沉积为主的砂层反射波弱于砾石层，波形以中、高频为主，同相轴具有弱连续性；对于洪冲积地区，地质雷达能分辨具有一定特征的地层单元，这为剖面图像的断层识别提供了标志；通过无人机正射影像技术对地质雷达测线进行地形校正，有利于获得更为准确的探测结果。 相似文献
7.
Yang Xiao-ping Li De-qing Zhao Cheng-bin Liu Bao-jin Sun Zhen-guo Zhao Jing-yao 《地震学报(英文版)》2004,17(1):94-102
Field experimental seismic sounding permitted us to obtain optimal shallow seismic reflection sounding parameters. In process
of data processing, we obtained a high-qualitative shallow seismic reflection sounding profile by using the techniques such
as filtering, edition surgical blanking, prediction deconvolution, fitting static correlation of first arrival time, and velocity
analysis. Comprehensive analysis on the information of reflection wave groups along the seismic sounding profile and the stratigraphic
and neogeochronological data obtained from many drills near the sounding line reveals that the upper termination of the detected
fault zone is located at depth of 75–80 m, in the Middle Pleistocene deposits dated to be about 220 ka BP. The continuity,
discontinuity, increasing and decreasing amount of reflection wave groups and change of their configurations, in combination
with geological columns of drills, permitted us to know that the width of upper termination of the fault zone is 100 m. It
can be inferred from the variation of number of reflection wave groups along the profile that the scarp of hidden fault is
200 m wide and the fault is a synsedimentary active fault in the Early Pleistocene and the early stage of Middle Pleistocene.
No tectonic movement, which offset the covering deposits, had occurred since the late stage of Middle Pleistocene.
Foundation item: A High-new Technique Project by State Development and Planning Commission of China (2001977). 相似文献
8.
Christopher Juhlin Hans Palm Carl-Fredrik Müllern Bo Wllberg 《Journal of Applied Geophysics》2002,51(2-4)
Two high-resolution reflection seismic profiles were acquired in the Heby area of eastern Sweden over glacial deposits for the purpose of mapping groundwater resources. The majority of shot points were located in clay resulting in good quality data along most of the profiles. On stacked and migrated sections, the uppermost clay is about 20 m thick and is characterized by its subhorizontal reflectivity. Sand/gravel deposits below it contain more dipping interfaces and have a chaotic reflectivity pattern. Depth to bedrock is interpreted to be 90 and 65 m on the respective profiles and occurs in about a 100-m-wide trough on both profiles. Reflections from the tops of sandy gravel zones generally have higher amplitudes. Clear reflections from a thin silt layer (20 cm thick) at about 10-m depth are observed on one of the profiles. Elastic finite difference modeling and the observation of this reflection in shot gathers show that the reflection is not an artifact of the acquisition nor the processing. The modeling also shows that there is no marked low-velocity waveguide in the near surface, but that an effective low Q zone may be present. Comparison with refraction profiling on the other profile shows that there is better agreement between the reflection seismic results and penetration tests than the refraction results with these tests. Both profiles allow the thickness of the overlying clay layers to be determined, as well as the thickness of the underlying sand/gravel deposits. This is important for estimating the amount of groundwater resources in an area. 相似文献
9.
浅层地震勘探资料地质解释过程中值得重视的问题 总被引：5，自引：5，他引：5
浅层地震勘探是第四系覆盖区隐伏断层活动性研究常用的手段,叠加剖面上反射波组的分叉、合并、弯曲、中断、尖灭等被用作判断断层存在的重要标志。松花江北的吕刚屯、巨宝屯浅层地震叠加剖面上,T0为下更新统砂砾石层等松散堆积和白垩系砂岩、泥岩的分界面,反射波组清晰。T0-1波组为砂砾石层和黏土层、或砂砾石层和粉细砂层的反射界面,反射波组振幅大,能量强。根据地震反射剖面和测线上的钻孔资料,认为阿什河断层错断了下更新统下段,滨州断层错断了上更新统下段。而通过建立高精度的钻探联合地质剖面、地层年代测试和地层对比,确认阿什河断层没有错断第四系,滨州断层错断了下更新统下段。最后,从第四系的岩性、厚度变化等解释了浅层地震叠加剖面上反射波组的中断、弯曲并非断层活动的结果,而是由第四纪地层相变引起的 相似文献
10.
Field-based studies of surficial volcanic deposits are commonly complicated by a combination of poor exposure and rapid lateral
variations controlled by unknown paleotopography. The potential of ground-penetrating radar (GPR) as an aid to volcanological
studies is shown using data collected from traverses over four well-exposed, Recent volcanic deposits in western Canada. The
deposits comprise a pumice airfall deposit (3–4 m thick), a basalt lava flow (3–6 m thick), a pyroclastic flow deposit (15 m
thick), and an internally stratified pumice talus deposit (60 m thick). Results show that GPR is effective in delineating
major stratigraphic contacts and hence can be used to map unexposed deposits. Different volcanic deposits also exhibit different
radar stratigraphic character, suggesting that deposit type may be determined from radar images. In addition, large blocks
within the pyroclastic deposits are detected as distinctive point diffractor patterns in the profiles, showing that the technique
has potential for providing important grain-size information in coarse poorly sorted deposits. Laboratory measurements of
dielectric constant (K') are reported for samples of the main rock types and are compared with values of K' for the bulk deposit as inferred from the field data. The laboratory values differ significantly from the "field" values
of K'; these results suggest that the effectiveness of GPR at any site can be substantially improved by initial calibration of
well-exposed locations.
Received: 10 May 1996 / Accepted: 27 December 1996 相似文献
11.
12.
Ground-penetrating radar (GPR) is a non-destructive geophysical technique to obtain information about shallow subsurface by transmitting electromagnetic waves into the ground and registering signals reflected from objects or layers with different dielectric properties. The present GPR study was conducted in Võhmuta limestone quarry in Estonia in order to describe the relationship between GRP responses to the variations in petrophysical properties. Sub-horizontally oriented cores for petrophysical measurements were drilled from the side wall of the quarry. The GPR profiles were run at the sloped trench floor and on the top of side wall in order to correlate traceable reflections with physical properties. Based on three techniques: (i) hyperbola fitting, (ii) wide angle reflection and refraction (WARR), and (iii) topographic, a mean electromagnetic wave velocity value of 9.25 cm ns?1 (corresponding to relative dielectric permittivity of 10.5) was found to describe the sequence and was used for time-to-depth conversion. Examination of radar images against petrophysical properties revealed that major reflections appear in levels where the changes in porosity occur. 相似文献
13.
Maksim Bano 《Geophysical Prospecting》2004,52(1):11-26
The attenuation of ground‐penetrating radar (GPR) energy in the subsurface decreases and shifts the amplitude spectrum of the radar pulse to lower frequencies (absorption) with increasing traveltime and causes also a distortion of wavelet phase (dispersion). The attenuation is often expressed by the quality factor Q. For GPR studies, Q can be estimated from the ratio of the real part to the imaginary part of the dielectric permittivity. We consider a complex power function of frequency for the dielectric permittivity, and show that this dielectric response corresponds to a frequency‐independent‐Q or simply a constant‐Q model. The phase velocity (dispersion relationship) and the absorption coefficient of electromagnetic waves also obey a frequency power law. This approach is easy to use in the frequency domain and the wave propagation can be described by two parameters only, for example Q and the phase velocity at an arbitrary reference frequency. This simplicity makes it practical for any inversion technique. Furthermore, by using the Hilbert transform relating the velocity and the absorption coefficient (which obeys a frequency power law), we find the same dispersion relationship for the phase velocity. Both approaches are valid for a constant value of Q over a restricted frequency‐bandwidth, and are applicable in a material that is assumed to have no instantaneous dielectric response. Many GPR profiles acquired in a dry aeolian environment have shown a strong reflectivity inside dunes. Changes in water content are believed to be the origin of this reflectivity. We model the radar reflections from the bottom of a dry aeolian dune using the 1D wavelet modelling method. We discuss the choice of the reference wavelet in this modelling approach. A trial‐and‐error match of modelled and observed data was performed to estimate the optimum set of parameters characterizing the materials composing the site. Additionally, by combining the complex refractive index method (CRIM) and/or Topp equations for the bulk permittivity (dielectric constant) of moist sandy soils with a frequency power law for the dielectric response, we introduce them into the expression for the reflection coefficient. Using this method, we can estimate the water content and explain its effect on the reflection coefficient and on wavelet modelling. 相似文献
14.
The upper 30 cm of the soil profile, which hosts the majority of the root biomass, can be considered as the shallow agricultural root zone of most temperate crops. The electromagnetic wave velocity in the soil obtained from reflection hyperbolas in ground-penetrating radar (GPR) data can be used to estimate soil moisture (SM). Finding shallow hyperbolas in a radargram and minimizing the subjective error associated with the hyperbola fitting are the main challenges in this approach. Nevertheless, we were motivated by the recent improvements of hyperbola fitting algorithms, which can reduce the subjective error and processing time. To overcome the difficulty of finding very shallow hyperbolas, we applied the hyperbola fitting method to reflections ranging from 27- to 50-cm depth using a 500-MHz centre-frequency GPR and compared the estimated moisture with vertically installed, 30-cm-long time-domain reflectometry (TDR) sensors. We also compared TDR and GPR sample areas in a 2-D plane using different GPR survey types and different hyperbola depths. SM measured with TDR and GPR were not significantly different according to Mann–Whitney's test. Our analyses showed that a root mean square error of 0.03 m3 m−3 was found between the two methods. In conclusion, the proposed method might be suitable to estimate SM with an acceptable accuracy within the root zone if the soil profile is fairly uniform within the application depth range. 相似文献
15.
Introduction Artificial seismic sounding is a geophysical exploration technique developed in prospectingfor oil and gas and other mineral resources and consists of reflection wave and refraction waveexploration methods. With rapid development of computer techniques and sounding instruments,the reflection wave method became a high-resolution imagery technique for underground struc-tures and is widespreadly used in detection of underground caves and in engineering exploration.In previous se… 相似文献
16.
Abstract Ground penetrating radar (GPR) and high‐resolution shallow reflection seismic surveying were carried out to investigate the subsurface geology in and around the Uemachi Fault zone in the Yamato River area, Osaka, Japan. Shallow drilling in the area showed a major displacement event during the middle Pleistocene. The main Uemachi Fault plane could be clearly imaged on the seismic section, except for the most shallow 200 m. Several shallow normal fault planes with less displacement could be detected on both sides of the fault plane. GPR profiles confirmed the presence of several shallow normal faults within the area near the fault zone. These shallow faults could be followed in all of the GPR profiles crossing the fault zone. The integration of seismic section, GPR profiles and drilling data led to a conceptual model that explains the evolution of the Uemachi Fault system. The proposed model suggests the occurrence of several cycles of small vertical displacement along the deep part of the fault plane caused by the regional east–west compressional stress. The ductile nature of the shallow sedimentary cover and the absence of confining pressure in the shallow part allow for a considerable amount of plastic bending before failing in the shallow sedimentary layers. This bending generates stretching force within the shallow sedimentary cover, which in time, along with gravitational force, gives rise to the formation of the swarm of normal faults within the shallow layers near the fault zone. Some of the detected faults extend to a depth of less than 3 m below the ground surface, suggesting that the last tectonic activity along the fault plane may have occurred recently. 相似文献
17.
《Journal of Applied Geophysics》2000,43(1):33-41
Ground-penetrating radar (GPR) experiments were conducted on a Quaternary sedimentary (made up of gravel, sand and loess) site to image the structures and tectonic features. Two sets of antennae, 50 and 100 MHz, have been tested in a water saturated alluvial deposits (mostly sand and gravel). The 100 MHz antennae provided adequate penetration depth and allowed better lateral continuity and resolution of the subsurface targets than the 50 MHz antennae. Results show that most of GPR data are contaminated by strong diffraction hyperbolae caused by above-ground objects near the survey line. Therefore, it is very important to recognize the diffractions through air and not to confuse them with the reflections from underground geologic features. Despite the air diffraction problem, the GPR data allow us to prospect subsurface sedimentary and tectonic structures. Water table, channels and meander bars are observed on GPR data. Most of these observations are correlated with borehole and trench data. 相似文献
18.
GPR study of pore water content and salinity in sand 总被引：5，自引：0，他引：5
High‐resolution studies of hydrological problems of the near‐surface zone can be better accomplished by applying ground‐probing radar (GPR) and geoelectrical techniques. We report on GPR measurements (500 and 900 MHz antennae) which were carried out on a sorted, clean sand, both in the laboratory and at outdoor experimental sites. The outdoor sites include a full‐scale model measuring 5 × 3 × 2.4 m3 and a salinity site measuring 7.0 × 1.0 × 0.9 m3 with three buried sand bodies saturated with water of various salinities. Our studies investigate the capability of GPR to determine the pore water content and to estimate the salinity. These parameters are important for quantifying and evaluating the water quality of vadose zones and aquifers. The radar technique is increasingly applied in quantifying soil moisture but is still rarely used in studying the problems of water salinity and quality. The reflection coefficient at interfaces is obtained from the amplitude spectrum in the frequency and time domains and is confirmed by 1D wavelet modelling. In addition, the GPR velocity to a target at a known depth is determined using techniques of two‐way traveltime, CMP semblance analysis and fitting an asymptotic diffraction curve. The results demonstrate that the reflection coefficient increases with increasing salinity of the moisture. These results may open up a new approach for applications in environmental problems and groundwater prospecting, e.g. mapping and monitoring of contamination and evaluating of aquifer salinity, especially in coastal areas with a time‐varying fresh‐water lens. In addition, the relationship between GPR velocity and water content is established for the sand. Using this relationship, a subsurface velocity distribution for a full‐scale model of this sand is deduced and applied for migrated radargrams. Well‐focused diffractions separate single small targets (diameter of 2–3 cm, at a depth of 20–180 cm and a vertical interval of 20 cm). The results underscore the high potential of GPR for determining moisture content and its variation, flow processes and water quality, and even very small bodies inside the sand or soil. 相似文献
19.
First-arrival traveltime tomography was applied to high-resolution seismic data acquired over a known quick-clay landslide scar near the Göta River in southwest Sweden in order to reveal the geometry and physical properties of clay-related normally consolidated sediments. Investigated area proved to be a challenging environment for tomographic imaging because of large P-wave velocity variations, ranging from 500 to 6000 m/s, and relatively steeply-dipping bedrock. Despite these challenges, P-wave velocity models were obtained down to ca. 150 m for two key 2D seismic profiles (each about 500-m long) intersecting over the landslide scar. The models portrait the sandwich-like structure of marine clays and coarse-grained consolidated sediments, but the estimated resolution (20 m) is too small to distinguish thin layers within this structure. Modelled velocity structures match well the results of reflection seismic processing and resistivity tomography available along the same profiles. 相似文献
20.
阐述了矩阵多分辨分析理论中的标准形式与非标准形式,并以Hilbert算子为例,说明了算子多分辨表示的压缩效果,为小波域偏移算法奠定了理论基础.从三维雷达波动方程出发,利用爆炸反射原理和浮动坐标变换,推导出三维探地雷达波动方程差分格式,并通过方程分裂算法及小波多分辨算法,在小波域求解波场外推矩阵,进而得到探地雷达小波域三维波动方程偏移算法,在此基础上,开发了探地雷达小波域偏移处理程序,并把该程序应用于三个球体空洞的3-D正演结果及实际的雷达数据中,通过对比偏移处理前后的雷达资料,得知该三维偏移算法能使3-D正演剖面中的反射波归位、绕射波收敛,极大地提高了雷达剖面的分辨率,有利于探地雷达资料的地质解释. 相似文献