Dilalos, SpyridonAlexopoulos, John D.Vassilakis, EmmanuelPoulos, Serafim E....
22页
查看更多>>摘要：The current study aims to clarify the structural regime of the deltaic valley of Pineios river (Thessaly, Greece). The structural control of a deltaic area is usually a crucial parameter for its Palaio-geographical evolution and the latter needs to be clear for the contemporary conservation of such a sensitive ecotope environmentally. The investigation of the concealed subsurface tectonic structures was accomplished through the combined interpretation of gravity measurements, VES and TEM soundings. The standard gravity data reduction has been carried out and the residual anomaly was isolated with the contribution of the Fourier filters. The Euler deconvolution has been applied, providing the corresponding depth solutions between 159.8 and 1716.6 m. In the context of the qualitative interpretation, we produced several structural maps (THDR, VDR, Tilt and Theta) in order to enhance the edges of density sources that may reflect fault zones. Severe indications for the delineation of fault zones of the area were provided by these maps. Moreover, 3D density models of the area have been constructed illustrating the subsurface density distribution, up to depths of 3370 m. A main zone of lower densities in the central part of the delta has been revealed, surrounded by three zones of higher densities. Afterwards, the densities of the majority of the existing geological formations were determined with laboratory measurements from geological specimens. Therefore, three geophysical-geological profiles have been constructed, based not only on the gravity modelling but also on the geological interpretation of the geoelectrical layered models from the VES and TEM measurements. In conclusion, concealed and unknown tectonic structures of the Pineios deltaic valley have been identified beneath the surface.
查看更多>>摘要：With the continuous exploitation of deep coal resources, the long-term stability control of surrounding rock of deep high stress soft rock roadway has become an urgent support problem. Because the traditional surrounding rock deformation zoning theory does not consider the creep effect of rock, it is not suitable for the support design of deep soft rock roadway, and can not ensure the long-term safe production of coal mines. This work proposes a novel four-stage strain-softening model based on rock creep characteristics, reveals the deformation zoning mechanism of surrounding rock in deep high stress soft rock roadway, and proposes the determination method of actual deep roadway surrounding rock zoning type and boundary stress. Moreover, taking Pan Yidong Coal Mine in China as an example, the feasibility and accuracy of the above theoretical method are verified by test, field monitoring and ABAQUS numerical simulation, and the influencing factors of the deformation zoning type of surrounding rock of the actual roadway are analyzed. The results show that the actual surrounding rock zoning type and boundary stress value determined by the deformation zoning mechanism of deep roadway surrounding rock in this paper are more accurate than the calculation results of the traditional deformation zoning theory, and the variations in the basic mechanical properties of surrounding rock and the strength of the in-situ stress field determined the number of actual deformation zones and the boundary stress values of each zone in the roadway surrounding rock. The research results can potentially aid the support designing and stability evaluation of deep roadway surrounding rock.
查看更多>>摘要：In-situ geophysical techniques based on electrical resistivity tomography were performed to determine the spatial and temporal distribution of heavy metals. This paper aimed to pursue a novel methodology consisting in combining electrical resistivity tomography measurements, soil chemical data, and statistical analysis to predict As and Cd distribution in paddy soils. The resistivity surveys were performed at 2 m depth in nine locations of Tolima district in Colombia. Chemical concentrations of both As and Cd were introduced in a standardization procedure to estimate their electrical resistivity values. Soil and fertilizers information were acquired to determine As and Cd input in the studied area. The laboratory standardization showed a direct linear regression for Cd and an inverse one for As. A high positive Spearman correlation between electrical resistivity and As / Cd content was determined, with 0.98 and 0.99 values, respectively. Results showed that As-like compounds were distributed mainly in shallower soil layers (0.45 m) and were characterized by lower electrical resistivity values (181-2318 omega.m). On the contrary, Cd-like compounds were observed in a deeper profile (0.80 m) with higher electrical resistivity values (559-4879 omega.m). This work underlies the utility of the combined geophysical techniques, soil chemical parameters and statistical analysis to improve the understanding of As and Cd dynamics and origin in topsoil, supporting the need of an agricultural management of paddy soils.
查看更多>>摘要：Anisotropy exists widely in the earth medium. For anisotropic medium, the traditional isotropic migration will lead to the inaccurate images and unfocused energy. Especially for a deep target exploration, ignoring anisotropy will further affect the subsequent seismic data interpretation. As an improved ray method, Gaussian beam migration overcomes the imaging problems of caustics and shadow zones in Kirchhoff migration, and avoids the time-consuming problems of wave equation migrations. However, the imaging quality of the Gaussian beam migration is controlled by the initial beam width at the surface. In this paper, we extend Nowack (2011)'s algorithm to anisotropic media and present an anisotropic dynamically focused beam migration by modifying the propagator of the Gaussian beams. We use anisotropic kinematic and dynamic ray tracing with optimized coefficients to obtain travel times, trajectories and dynamic information. We then use dynamically focused beams for weakly anisotropic media to calculate the Green's function and the Claerbout imaging condition to obtain images. This strategy enables us to improve the imaging quality in the middle and deep layers without reducing the imaging quality in the shallow layers, which will help to overcome the limitation of the initial beam width in Gaussian beam migration. The results for a VTI fault model and the Shengli complex structure model show the accuracy and validity of the proposed method in this paper.
查看更多>>摘要：The airborne transient electromagnetic method (ATEM) has become a popular tool in mineral and resource exploration due to its speed and high efficiency. The distance between two adjacent measured points is minuscule for a flight line because of the oversampling in the ATEM, which results in a sharp change in the horizontal direction. The conventional lateral constraint inversion method accumulates errors and has a significant calculation cost. Therefore, a laterally constrained, segmented inversion method based on a reference point is proposed to reduce errors and improve accuracy. Electrical information about the known logging data is employed as the lateral constraint of the reference point; alternatively, the inversion results of previous point can be used as lateral constraints, which guarantees a continuous inversion profile. The golden-section method is applied to solve the Lagrange multiplier to ensure a quick and effective convergence of inversions. Constraint inversions of a one-dimensional model show that the strategy converges quickly, and the inversion results are closer to the true resistivity of the model. Constraint inversion of a 2D model indicates that lateral constraints considerably reduce the discontinuity of a single-point inversion and smooths the inversion's resistivity pseudosection. Finally, the effectiveness of the proposed algorithm is verified by the inversion of the airborne transient electromagnetic survey data in Xinjiang province.
Porras, DanielCarrasco, JavierCarrasco, PedroGonzalez, Pablo J....
13页
查看更多>>摘要：Seismic hazard assessment of present-day tectonic faults may be improved by studying their structure and kinematics. These features have been mainly determined by surface geological studies of exposed fault traces, structural lateral segmentation or paleoseismic trenches. All these approaches rely mainly on two-dimensional analyses of surface outcrops, while knowledge of the faults at depth remain largely inaccessible. To improve on such limitations, geophysical methods can be applied to establish detailed information on fault morphology and segmentation at depth. This work analyzes new results of a deep electrical resistivity tomography survey acquired across the Baza Fault, a present-day tectonic fault that controls the geometry of the Neogene intramountainous Baza Basin (Betic Cordillera, Spain). Interpretation of our preferred resistivity model reveals its detailed structure down to approximately 1000 m depth. The survey shows a minimum 2 km wide complex normal fault system, with rotational tilting blocks bounded by potentially listric normal faults. This study presents subsurface evidence of the Baza fault (F3), coincident the main topographic scarps. However, the geophysical model and geomorphic evidence also support a fault branch (F1) that might be an additional active seismogenic source. The geophysical survey technique presented in this study provides essential data to improve assessment of the seismogenic potential of the Baza Fault.
查看更多>>摘要：Underground traffic systems are a major generator of high-frequency ground vibrations in urban regions. Subway-induced ground vibrations are identified from seismic records at a seismic station on a designed monitoring site with curved railroad tracks. Subway-induced ground vibrations appear in diffusive and periodic wavelet packets. The ground vibrations are mainly composed of harmonic energy that appears at frequencies in integer multiples of fundamental frequencies. Wheel rotations are a primary source of impulsive signals. The separation distances of wagon wheels lead to the production of periodic time signals. The frequency contents of ground vibrations are controlled by subway speed. The frequency contents are different between outer-circle and inner-circle tracks due to differences in subway speeds, which is consistent over time. The ground vibrations at frequencies >60 Hz are highly affected by ambient noises and vary seasonally. The railway-vehicle configuration and subway speeds modulate the spectral contents. Subway-induced signals are a consequence of various combinations of signals from regularly distributed wagon wheels. The subway speed and wagon configuration can be inferred from the subway-induced signals.
查看更多>>摘要：Rayleigh waves in oil exploration seismic records usually have strong energy and are considered as noise, but Rayleigh waves also carry information about subsurface. In this paper, we process Rayleigh waves from a set of oil seismic data to detect underground structures of shear-wave velocity (vs) using multi-channel analysis of surface waves (MASW). Fundamental mode and higher order mode dispersion curves of the Rayleigh wave were automatically extracted by a modified phase shift method. We then use the genetic and damped least squares (DLS) joint inversion algorithm to inverse the dispersion curves and obtain a one-dimensional (1D) vs structure under each shot gather. Finally, all 1D vs structures were combined to create a 3.2 km long two-dimensional (2D) section, revealing a stratum structure down to 80 m depth. The results show that MASW technology successfully improves the use of oil seismic data, the automatic dispersion extraction method based on modified phase shift improves the efficiency of data processing, and the joint inversion algorithm reduces the dependence of the Rayleigh wave dispersion inversion on initial model.
查看更多>>摘要：Dhanjori formation, a significant member of Singhbhum Craton, Eastern India, is well-known for its complex mineralogical character and huge content of Au-mineralization. This 2.1 Ga old Paleoproterozoic formation is composed of siliciclastic metasedimentary rocks interlayered with mafic/ultramafic volcanic rocks. Traces of gold has been spotted by many researchers in the sulfide-hosted mafic-ultramafic volcanic rocks and quartz pebble conglomerate units by different studies. Regional Audio Magnetotelluric (AMT) survey was conducted in 10 kHz-10 Hz frequency range over various lithological units of Dhanjori and adjacent Iron Ore Group. The key challenge faced during the analysis of magnetotelluric (MT) data is due to the presence of near-surface heterogeneities. The amplitude of the MT response gets distorted by galvanic effects which further create difficulties in modelling and inversion. If the effect is not removed in advance, it might lead to erroneous subsurface modelling and interpretations. On the contrary, the phase tensor data does not show any change in values even in the presence of galvanic distortion. Though phase tensors are the computed values from impedance tensor, still the response is free from any shallow level ambiguities unlike impedance data. We have performed 3-D inversion of phase tensor data to generate a conductivity model of Dhanjori basin. The objective was to verify whether the inclusion of phase tensor components in the inversion routine was able to provide some extra information that might add value to the analysis. Model from phase tensor inversion indicates only relative variation in the subsurface conductivity structure due to lack of amplitude information in the data. Hence, we also performed 3D joint inversion including both impedance and phase tensor components for obtaining the final conductivity model of Dhanjori to recover the absolute subsurface conductivity structure unaffected by galvanic distortion. Correlation of the conductivity model with available geoscientific information in Dhanjori and adjacent geological units helped us to relate the conductors to the sulfide mineralization prospect.
查看更多>>摘要：Semi-airborne Transient Electromagnetics (SATEM) is a low-cost and productive method for quick geophysical surveys. The system includes a grounded line source on the ground and a receiver coil hanging in the air by a drone. Motion noise usually has the biggest impact on the acquired data because the receiver coil, which is suspended several meters below the drone by a soft rope, would maintain continuing random motion due to the movement of the drone, wind, etc. It also is a common problem in airborne electromagnetic (AEM) surveys, which typically use fixed-wing aircraft or helicopters. However, due to the secondary-field acquisition of SATEM, there are data deviations between the start and end of each motion period caused by continuous coil motion and discontinuous data acquisition. And this also brings difficulty in baseline elimination by using most de-noising methods, which require time or signal continuity on the baseline and are widely applied in full-time acquisition data (full-wave data). We proposed a simple but useful single-period polynomial-fitting method to remove motion noise from secondary-field data. And to prevent the obtained polynomial from being distorted from baseline by valid signals, a haar-based wavelet was employed to automatically recognize the start-point of pulses in the original signal so that the pulse can be eliminated before the polynomial-fitting process. Through a field SATEM survey data test, we found that the polynomial-fitting with 5 parameters (4th order) is good enough to describe the motion characteristics. We compared the results with those of the most commonly used wavelet methods at different bases and levels. The comparisons of de-noising results and apparent resistivity profiles of the original signal, data after wavelet de-nosing, and data after the polynomial-fitting de-noising show that this method is superior and much more reliable than wavelet de-noising of secondary-field SATEM data.
NSTL
Elsevier