To improve inversion accuracy of ambient noise surface wave (ANSW) data in the near surface, we propose a kernel fuzzy C-means (KFCM) clustering-constrained inversion scheme. The scheme incorporates a kernel clustering constraint term into the objective function, which is guided by a priori cluster centers during the inversion process. The effectiveness of the proposed method is validated using both synthetic and field data. In the synthetic tests, the KFCM clustering-constrained inversion reduces model-space errors and yields clearer separation of clustered Vs regimes than the fuzzy C-means (FCM) clustering-constrained inversion using the same a priori centers. Compared with Tikhonov smoothing regularization, KFCM better preserves regime boundaries and velocity contrasts. For the field case, the KFCM clustering-constrained inversion accurately delineates two stratigraphic interfaces consistent with the borehole Vs logs, whereas the Tikhonov smoothing-constrained and FCM clustering-constrained inversion methods results show larger deviations with borehole data. The results demonstrate that the KFCM-constrained is an effective and valuable scheme for the inversion of ANSW data in the near surface. It can also be applied to other geophysical data.

The Gamburtsev Subglacial Mountains (GSMs) in the interior East Antarctic Craton are entirely buried under the massive East Antarctic ice sheet, with a ~50–60 km thick crust and ~200 km thick lithosphere, but little is known of the crustal structure and uplift mechanism. Here, we use airborne gravity and aeromagnetic anomalies for characteristic analysis and inverse calculations. The gravity and magnetic images show three distinct geophysical domains. Based on the gravity anomalies, a dense lower crustal root is modelled to underlie the GSMs, which may have formed by underplating during the continental collision of Antarctica and India. The high frequency linear magnetic characteristics parallel to the suture zone suggest that the upper crustal architecture is dominated by thrusts, consisting of a large transpressional fault system with a trailing contractional imbricate fan. A 2D model along the seismic profile is created to investigate the crustal architecture of the GSMs with the aid of depth to magnetic source estimates. Combined with the calculated crustal geometry and physical properties and the geological background of East Antarctica, a new evolutionary model is proposed, suggesting that the GSMs are underlain by part of a Pan-African age advancing accretionary orogen superimposed on Precambrian basement.

Adequate knowledge of velocity is required for accurate data imaging and depth conversion, as well as for quantifying the distribution of soil water content. Without complementary borehole information in the form of dielectric permittivity and/or porosity logs along the profile, it is currently impossible to reliably estimate the high-frequency electromagnetic velocity distribution in the probed subsurface region. Here, we present a new method for calculating the precise subsurface velocity structure from ground penetrating radar (GPR) reflection data that does not require boreholes or log data. This study investigates the ability of the pulse_EKKO PRO GPR system to predict a vertical profile for the possible velocity estimation of a layered and contaminated geophysical test site in Hangzhou, China. All data were acquired and saved on the GPR system in various files (projects) before analysis using GPR software to obtain approximated velocity modelling using common midpoint (CMP) gathers. Using the velocity spectrum analysis, a vertical profile of the interval velocities can be derived from each CMP gather. The findings of this study indicate that the proposed method is effective and sustainable. Furthermore, owing to the efficacy of the method in terms of field effort and computational complexity, it can easily be expanded to 3D GPR velocity exploration, increasing its importance in comparison to standard offset-based techniques for estimating velocity using GPR.

<p>The Gamburtsev Subglacial Mountains (GSM) in central East Antarctica are  completely buried beneath the East Antarctic Ice Sheet. The GSM are known to be underlain by anomalously thick crust (~50–60 km) and ~200 km thick Precambrian lithosphere, but their crustal-scale geology remains less well- studied. Little is known about the 3D heterogeneity in crustal architecture beneath the GSM, and how this may relate to larger-scale tectonic processes responsible for Gondwana amalgamation.</p> <p>Here, we use airborne gravity and aeromagnetic anomalies to explore the crustal architecture of the GSM in unprecedented detail. The gravity and magnetic images show three distinct geophysical domains, and a dense lower crustal root is modelled beneath the northern and central domains. We propose that the root may reflect magmatic underplating, associated with Pan-African age back-arc basin formation and inversion, followed by the collision of Australo-Antarctica and Indo-Antarctica. The high frequency linear magnetic patterns parallel to the Gamburtsev Suture zone, suggest that the upper crustal architecture is dominated by thrust and strike-slip faults, formed within a large-scale transpressional fault system.</p> <p>We calculated a 2D gravity and magnetic model along a passive seismic profile to investigate the crustal architecture of the GSM, with the aid of depth to magnetic source estimates.   By combining the crustal model with  geological constraints, we propose a new evolutionary model suggesting that the crust of the northern and central GSM domains formed part of a cryptic accretionary orogen, of proposed Pan-African (~650-550 Ma?) age. The inferred accretionary stage was followed by continental collision (~540-520 Ma?) along the Gamburtsev suture, which is linked here to Gondwana amalgamation.</p>

Polarization is an important technique for ground penetrating radar (GPR) surveys, particularly when deter-mining the shape, orientation, size, and precise location of any buried material. A linearly-polarized incident GPR wave experiences polarization change upon scattering from the host medium, which highly depends upon the technique and antenna orientation used for the acquisition of the GPR data. This paper focuses on the po-larization of GPR data acquired at a laboratory test site. We kept the GPR antenna orientation and geometry in mind to understand how they impact the results while detecting subsurface contamination. Because of its direct indication ability, amplitude variation with offset (AVO) has been widely used to detect subsurface contami-nation; however, a technique to evaluate the distribution of subsurface contamination is not yet available; thus, in this study, we will also discuss the distribution of contamination using polarization of GPR data. Two major phenomena have been studied: the polarity of the data acquired and slice view with and without contamination in the testing tank, as well as trace, frequency, and amplitude plot during data analysis to determine the dif-ference of plot with and without contamination. Our findings suggest that using the polarization geometry technique to obtain an accurate view of the subsurface contamination will not only improve the GPR AVO analysis but will also provide a clear distribution of contamination in the subsurface.

The limited bandwidth of a single source normally restricts the imaging resolution for the subsurface target. Multi-frequency acquisition is a promising way to enhance the resolution with reasonable data fusion. An Ormsby wavelet based theoretical study confirms the significance of both the low and high frequencies for improving the resolution by means of peak duration and side-lobe oscillation level. To avoid over-boosting the noise during the data fusion, we propose a joint deconvolution approach to associate the single-frequency data with the target function directly. A weighted matched filter is accordingly derived based on the signal-to-noise ratio of the multi-frequency data. Error analysis shows that the joint weighted deconvolution based data fusion achieves better noise control compared to the direct-summation based deconvolution. Both wedge model based synthetic result and ground penetrating radar acquired field data example confirm the effectiveness of the proposed data fusion approach on resolution enhancement.

Ground-penetrating radar (GPR) is one of the most important techniques for obtaining high-resolution data in archaeological research, and it is becoming increasingly important. The continuous wavelet transform (CWT), which is non-numerical technique, gives an overcomplete representation of a signal by continuously varying the wavelet’s translation and scale parameters in the time series dataset. This paper focuses on the novel technique of integrating CWT and the wavelet transform maxima (WTM) to extract information from an archaeological test site in south-eastern China. For the characterization of archaeological features, we assessed the importance of dense and accurate data collection as well as GPR signal processing. The mathematical formulation and applicability of GPR attributes, particularly amplitude-based attributes, to identify and characterize archaeological buried targets are also discussed. GPR data is acquired using co-polarized and cross-polarized configurations with transverse-electric (TE) and transverse-magnetic (TM) broadside frequency plates at 100 and 200 MHz. Next, CWT was applied using six different wavelet levels, followed by amplitude comparison. The archaeological targets were successfully interpreted using peak amplitude and CWT. The proposed methodology has significantly improved data visualization and interpretation of GPR data, and it also gave us good results in identifying archaeological anomalies.

Accurate understanding of near-surface structures of the solid earth is challenging, especially in urban areas where active source seismic surveys are constrained and difficult to perform. The analysis of anthropogenic seismic noise provides an alternative way to image the shallow subsurface in urban environments. We have developed an application of using traffic noise with seismic interferometry to investigate near-surface structures in Hangzhou City, Eastern China. Noise data were recorded by dense linear arrays with approximately 5 m spacing deployed along two crossing roads. We analyze the characteristics of traffic-induced noise using 36 h continuous recordings. Coherent Rayleigh surface waves between 2 and 20 Hz are retrieved based on crosscorrelations within 1 h time windows. Robust phase-velocity dispersion curves are extracted from virtual shot gathers using multichannel analysis of surface waves and coincide with the results from active seismic data, noise beamforming analysis, and measurements with the spatial autocorrelation method. S-wave velocity profiles are derived for the top 100 m of the subsurface at the array locations. The estimated S-wave velocities from traffic noise correspond to the velocities estimated from logging data. The 2D S-wave velocity maps reveal different soil deposits and bedrock structures in the estuarine sedimentary area. The results demonstrate the accuracy and efficiency of delineating near-surface structures from traffic-induced noise, which has great potential for monitoring subsurface changes in urban areas.

Electrical well-logging techniques, combined with electrical conductivity models, have been widely used to estimate oil saturation levels in hydrocarbon reservoirs. For complicated and heterogeneous petroleum reservoirs, however, evaluation results are inevitably limited by well locations. Recent studies have indicated that the borehole–surface electromagnetic method (BSEM) can detect electrical characteristics distal from a well, and it can be applied to delineate the boundaries of complicated reservoirs. Therefore, in the study described here, a new method to estimate reservoir oil saturation, based on the BSEM, has been developed. In this work, we deployed the BSEM in a designated study area, obtaining complex resistivity and polarizability data, through the constrained inversion of the re-weighted regularized conjugate gradient method. Based on the petrophysical analyses, we developed a new saturation evaluation model, composed of a parallel circuit connection between formation water and the polarization induced by the porous medium containing clay minerals. The effectiveness of the new model was verified with a synthetic dataset generated using Archie's law and the improved Dias model. We found that the target reservoir oil saturation results calculated using the new oil saturation model were in good agreement with applicable nuclear magnetic resonance log data, thus verifying the validity of this new BSEM evaluation technique.

Near surface geophysical methods have been used extensively as non-invasive and cost-effective methods to characterize subsurface geological properties over the past two decades. Since these approaches are able to illustrate the temporal and spatial changes of geological conditions, they are applied for the characterization of landslide zones. Landslides are one of many natural disasters that cause life and property losses. Landslide mechanisms are affected by topsoil materials, bedrock geometry, and subsurface water content. This paper presents study results for a landslide area located in the Xiaoshan district in Hangzhou City, China. The 2D seismic P-wave refraction tomography (SRT) and 2D electrical resistivity tomography (ERT) methods were used to characterize the landslides in this area. The ERT technique was applied using four lines over and outside of the landslide scar using the Wenner electrode configuration. The SRT study was performed along four longitudinal profiles coincident with the ERT lines. Samples from two boreholes, located on two different profiles, and SEM-EDS (Scanning Electron Microscopy-Energy Dispersive Spectroscopy) testing provided calibration for of ERT and SRT measurements. The results of the combined techniques have defined the layers associated with sand and high clay content as well as the geometry of failure surfaces.

The development of geophysical methods has increased the relevance of seismic surveys on near-surface geological structures in urban areas. In recent years, one important issue faced by many scholars is how to effectively increase the signal-to-noise ratio of seismic signals and improve the resolution of seismic information. Near-surface layers typically exhibit low velocity and severe lateral velocity variation characteristics due to weathering. Loose structures in a near-surface condition caused by weathering indicate low quality factor, resulting in the intensive absorption of seismic waves passing through these layers, which ultimately limits the effectiveness of information acquired from the received spectrum. To facilitate the investigation of geological conditions such as bedrock surface undulations and hidden structural faults underground in the Second Stage of Qianjiang New Town, Hangzhou City, an analysis of shallow surface attenuation compensation based on downhole seismic data is conducted. In addition, based on the downhole seismic data, the quality factor Q of underground strata was obtained using a spectral ratio method, and the inverse Q filtering was applied to a stacked seismic reflection section in Hangzhou. A set of shallow surface absorption and attenuation compensation techniques suitable for the Second Stage of Qianjiang New Town, Hangzhou City is developed, which can effectively improve the resolution and detection accuracy of seismic sections and provide reliable seismic data and reference methods for future exploration and development in this area.

Archaeological GPR data from antennas of different frequencies allow the identification of buried cultural heritage at different scales. Therefore, multi-frequency GPR systems are recommended for complicated subsurface archaeological conditions. GPR data fusion approaches, automatically or semi-automatically, can integrate data measurements from different frequency antennas, combine them into a single representation, and partially overcome the unavoidable trade-off between penetration and resolution. We propose an adaptively weighted fusion method for multi-frequency GPR data based on genetic algorithms (GAs). In order to evaluate the feasibility and the effectiveness of the strategy for archaeological prospection, we tested the procedure on GPR datasets acquired in two totally different archaeological conditions: rammed layers of an ancient wall, in Henan Province, China, and complex and elusive prehistoric archaeological features within a natural stratigraphic sequence on the volcanic Stromboli Island, Italy. The results demonstrate that the proposed strategy can maximize the information content of GPR profiles, enhancing the GPR interpretation possibilities in an automatic and objective way for different targets and in different subsurface conditions.

随着中国经济的快速发展和城市化进程的加快,有限的土地资源和城市发展之间的矛盾越来越突出,城市地下空间的安全、合理利用和地质环境保护具有重要的战略意义.为了解决G20、亚运会以及数字经济为杭州市快速发展带来的人口快速增长与土地资源有限的瓶颈问题,针对以杭州为代表的南方丘陵地区地下空间精细探测需求,开展了弹性波法、电法与电磁法等多种地球物理方法的可行性研究.结果 表明:不同勘探方法在探测深度、分辨率以及勘探效率上具有明显的差异性,需要根据地下地质状况以及地表条件选择合适的勘探方法进行探测,这对类似丘陵地区城市地下空间开发及利用具有指导意义和参考价值.

Within electrical resistivity tomography (ERT), the selection of arrays and electrode locations can effectively enhance the resolution of imaging. By properly selecting and optimizing the survey design, a better resolution will be obtained with fewer electrodes and configurations than traditional arrays. Previous work has demonstrated that the optimized survey design using the ‘Compare R’ method can provide better resolution than conventional arrays. This paper adds target-oriented selection and modified the original ‘Compare R’ method. The modified method first selects the target area in the comprehensive data sets, then optimizes the choice by the modified CR method, and finally combines the optimization results of multiple sets of target areas. For the target area, this method can select fewer electrodes and arrays than the original CR method, get better resolution than conventional arrays, and take less calculation time.

In urban areas, dense buildings, traffic road networks, and concrete floors severely restrict geoelectric methods, preventing the arrangement of ideal straight lines or grid survey layouts. We present herein an optimized three-dimensional (3D) electrical resistivity tomography (ERT) survey design based on arbitrarily distributed electrodes with a dipole–dipole array as the basic unit. Each unit is independent and can be randomly distributed and adjusted in length. The component electrodes can be used as current or potential electrodes as required. This method can eliminate the limitations of grids and cables. However, the random distribution of electrodes does not mean that there are no restrictions, as one must optimize the most suitable ones based on measurements showing data volumes that far exceed those of conventional survey designs. The compared target resolution by batch method is used as the optimized array. It focuses on the target area and filters out data before the Compare-R calculation is applied. This is faster than the traditional Compare-R algorithm due to its batch calculation. Furthermore, the frequency of electrodes was analyzed to reduce the number of electrodes used while maintaining good results. A field example with drilling information verification demonstrates the effectiveness of the method. We use the adjusted optimization method for the random distribution of electrodes in the exploration design, achieving good imaging results in combination.

One of the most widely used geophysical surveying techniques in the urban environment is the electrical resistivity tomography (ERT) method. However, traditional ERT can only utilize regular grid and equidistant electrode layouts. Furthermore, all electrodes must be connected by long cables, and the existence of obstacles in urban environments makes it challenging to implement such layouts. We therefore present an optimized 3D ERT survey design consisting of arbitrarily distributed electrodes. We use the dipole-dipole array as the data acquisition unit. Each unit is independent and can be randomly distributed and adjusted in length. The unit can be used as a current or potential electrode as required. In this way, the limitations of grids and cables can be eliminated. Arbitrary distribution does not mean doing whatever you want. Must follow the basic principles of the geoelectric method. Based on this, we have formulated a set of reasonable procedures in the survey design, including the ‘main-sub unit’ and the ‘effective measurement circle’, which make the surveying system run more quickly and accurately. We select a complex urban area with partial prior information as the field sample to verify our survey design. This approach can effectively avoid the disadvantages of the traditional ERT method and obtain correct and effective results in a complex urban environment.

True tri-axial sanding fracturing experiments are carried out on conglomerate samples from the Permian Wuerhe Formation of Mahu sag, Junggar Basin, to study hydraulic fracture propagation geometry and quartz sand transport in matrix-supported fine conglomerate and grain-supported medium conglomerate. The effect of rough fracture surface on conductivity is analyzed using the 3D-printing technology to reconstruct the rough surface formed in the fractured conglomerate. The hydraulic fractures formed in the matrix-supported fine conglomerate are fairly straight, and only more tortuous when encountering large gravels at local parts; thus, proppants can get into the fractures easily with transport distance about 70%–90% of the fracture length. By contrast, in the grain-supported medium conglomerate, hydraulic fractures tend to bypass the gravels to propagate in tortuous paths and frequently change in width; therefore, proppants are difficult to transport in these fractures and only move less than 30% of the fracture length. As the matrix-supported fine conglomerate has high matrix content and low hardness, proppants embed in the fracture surface severely. In contrast, the grain-supported medium conglomerate has higher gravel content and hardness, so the quartz sand is crushed more severely. Under the high proppant concentration of 5 kg/m2, when the closure stress is increased (above 60 MPa), fractures formed in both matrix-supported fine conglomerate and grain-supported medium conglomerate decrease in width significantly, and drop 88% and 92% in conductivity respectively compared with the case under the low closure stress of 20 MPa. The field tests prove that under high closure stress above 60 MPa, using a high proportion of fine proppants with high concentration allow the proppant to move further in the fracture; meanwhile proppant places more uniformly in the rough fracture, resulting in a higher fracture conductivity and an improved well performance.

The velocity of near-surface materials is one of the most important for Ground-Penetrating Radar (GPR). In the study, we evaluate the options for determining the GPR velocity to measure the accuracy of velocity approximations from the acquired GPR data at an experimental site in Hangzhou, China. A vertical profile of interval velocities can be estimated from each common mid-point (CMP) gather using velocity spectrum analysis. Firstly, GPR data are acquired and analyzed using the popular method of hyperbola fitting which generated surprisingly high subsurface signal velocity estimates while, for the same profile, the Amplitude variation with offset (AVO) analysis of the GPR data (using the same hyperbola fitting method) generate a more reasonable subsurface signal velocity estimate. Several necessary processing steps are applied both for CMP and AVO analysis. Furthermore, experimental analysis is conducted on the same test site to get velocities of samples based on dielectric constant measurement during the drilling process. Synthetic velocities generated by AVO analysis are validated by the experimental velocities which confirmed the suitability of velocity interpretations.

Landslide monitoring can characterize subsurface water percolation, hydrogeological conditions, and slope stability over time. In other words, the aim of the time-lapse method is to a better understanding of water circulation and its effect within the landslide body. The presence of water-saturated materials is one of the main triggering factors on the potential of sliding mass in Xiaoshan district, Hangzhou city, China. In this paper, spatiotemporal changes of the water content are monitored by two applied geophysical methods: 2D time-lapse electrical resistivity tomography (TLERT) and 2D P-wave time-lapse seismic refraction tomography (TLSRT). Time-lapse electrical resistivity is performed by the Wenner alpha array due to its ability to display high vertical resolution of subsurface images and signal-to-noise ratio. Time-lapse seismic refraction tomography is conducted as individual models corresponding to time-lapse electrical resistivity images. The validity of the method is examined by analyzing travel time curves and seismograms. Two geophysical methods were conducted along the two profiles spread out over the failure surface. Specific observations are a disparity of characterization of the water contents between the two dates scheduled for August and November 2018. Using electrical resistivity tomography monitoring, the landslide body and mass were characterized by increasing the resistivity related to more evaporation, boulders, and tree roots on the top surface and decreasing in greater depth in the wet season. In this study, time-lapse seismic refraction tomography represents the presence of high seismic velocity values in unsaturated materials, which can violate the Biot–Gassmann relationship. Good agreement between the results of the two geophysical methods can illustrate the landslide geometry and possible sliding hazard by characterizing the moisture content and changes of clay content over two different periods. In this paper, the material compositions are supported by previous borehole data.