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1.
2003年2月24日新疆巴楚—伽师地区发生MS6.8地震,出现了唐山地震、海城地震后近30年我国大陆最具规模的砂土液化现象。大量研究显示,巴楚地震液化砂土标贯击数与锥尖阻力指标偏大,采用国内外液化判别方法往往会判为非液化。利用Robertson土质分类图对巴楚地区孔压静力触探试验（CPTU）数据进行土类分层检验,基于以下原则,选定了液化点液化层与非液化点临界液化层。（1）应选取非液化点土层剖面中最易液化层,不能因液化点力学指标偏大而将非液化点临界液化层力学指标选得更大;（2）应结合qc-h与Rf-h图,避免选取黏土为液化层;（3）巴楚地区液化层往往上覆非饱和细砂,形成透水边界,选取液化层时应舍弃存在透水边界的土层。最后,利用我国规范方法构建了巴楚地震静力触探（CPT）液化数据库,并进行了初步的判别分析。 相似文献
2.
Daniel B. Chu Jonathan P. Stewart Shannon Lee J. S. Tsai P. S. Lin B. L. Chu Raymond B. Seed S. C. Hsu M. S. Yu Mark C. H. Wang 《Soil Dynamics and Earthquake Engineering》2004,24(9-10):647
The 1999 Chi–Chi, Taiwan, earthquake provides case histories of ground failure and non-ground failure that are valuable to the ongoing development of liquefaction susceptibility, triggering and surface manifestation models because the data occupy sparsely populated parameter spaces (i.e. high cyclic stress ratio and high fines content with low to moderate soil plasticity). In this paper, we document results from several large site investigation programs conducted in Nantou, Wufeng and Yuanlin, Taiwan. The seismic performance of the investigated sites include non-ground failure building and free-field sites, building sites with partial foundation bearing failures, free-field lateral spread sites, and free-field level ground sites with sediment boils. Field and laboratory investigation protocols for the sites are described, including cone penetration testing (some with pore pressure and shear wave velocity measurements) and rotary wash borings with standard penetration testing (including energy measurements). Implications of the SPT energy measurements with respect to established guidelines for the estimation of SPT energy ratio (including short rod corrections) are presented. Finally, data for three example sites are shown that illustrate potential applications of the data set, and which also demonstrate a condition where existing liquefaction analysis procedures fail to predict the observed field performance. 相似文献
3.
Neurofuzzy mapping of CPT values into soil dynamic properties 总被引：1，自引：0，他引：1
Ever since the early days of soil mechanics there has been a strong tendency to develop correlations between easy-to-obtain parameters and mechanical properties of geotechnical materials. This interest has not decreased as more elaborated methods have been proposed. On the contrary, once a method under development reaches certain degree of sophistication, researchers usually devote a great deal of time to establish simplified procedures. The study presented in this paper follows a similar path in the sense that a data-based knowledge procedure instead of mathematically based methods is used to develop a manner to estimate soil dynamic properties directly from cone-tip penetration resistances. This method is based on a hybrid system integrated by merging artificial neural networks and fuzzy logic. The procedure is evaluated comparing its results with actual measurements of cone-tip penetration resistances and shear wave velocities done in twin borings. 相似文献
4.
Seismic piezocone (SCPTu) data compiled from 86 sites in the greater Christchurch, New Zealand area are used to evaluate several existing empirical correlations for predicting shear wave velocity from cone penetration test (CPT) data. It is shown that all the considered prediction models are biased towards overestimation of the shear wave velocity of the Christchurch soil deposits, demonstrating the need for a Christchurch-specific shear wave velocity prediction model (McGann et al., 2014) [1]. It is hypothesized that the unique depositional environment of the considered soils and the potential loss of soil ageing effects brought about by the 2010–2011 Canterbury earthquake sequence are the primary source of the observed prediction bias. 相似文献
5.
Model uncertainty is introduced into direct-current resistivity data by adding random changes to layer thicknesses in a ten-layer model. The resulting information is then aliased by generating a sounding curve which contains less information than the ten resistivities and nine thicknesses. These sounding curves are then inverted via the Backus-Gilbert algorithm using singular value decomposition to obtain solutions in terms of simpler two-or three-layer models. Quantitative results confirm what has been known qualitatively for many years as the principle of equivalence. An interesting result is that the geometric average of a given suite of noisy models is virtually identical to the best-fit model for the average of the noisy curves. The results show that the inversion of resistivity data by nonlinear least-squares parameter fitting is stable in the sense that noise in the data inverts to the same magnitude of noise in the model. 相似文献
6.
Hydrocarbon prediction from seismic amplitude and amplitude‐versus‐offset is a daunting task. Amplitude interpretation is ambiguous due to the effects of lithology and pore fluid. In this paper, we propose a new attribute “J” based on a Gassmann–Biot fluid substitution to reduce ambiguity. Constrained by seismic and rock physics, the J attribute has good ability to detect hydrocarbons from seismic data. There are currently many attributes for hydrocarbon prediction. Among the existing attributes, far‐minus‐near times far and fluid factor are commonly used. In this paper, the effectiveness of these two existing attributes was compared with the new attribute. Numerical modelling was used to test the new attribute “J” and to compare “J” with the two existing attributes. The results showed that the J attribute can predict the existence of hydrocarbon in different porosity scenarios with less ambiguity than the other two attributes. Tests conducted with real seismic data demonstrated the effectiveness of the J attribute. The J attribute has performed well in scenarios in which the other two attributes gave inaccurate predictions. The proposed attribute “J” is fast and simple, and it could be used as a first step in hydrocarbon analysis for exploration. 相似文献
7.
Oziel Souza de Araújo Eduardo Chemas Hindi Augustinho Rigoti Fábio Henrique Rigoti 《Geophysical Prospecting》2019,67(7):1965-1976
Geophysical investigations using conventional techniques applied to groundwater exploration can often present strong limitations involving high financial costs, complex acquisition logistics and high ambiguity in results. Dispersion of the electric current flow, induced polarization) effects, cultural noises and shallow lateral heterogeneities represent the main problems faced by geoelectric methods in these types of surveys. Moreover, elements such as intrusions and mineralization at different depths may be responsible for signal attenuation as well as high resistivity in unsaturated zones and complex three-dimensional formations or clayey zones cause variations in the electric current. The focused source electromagnetic and differentially normalized method approaches can help to solve some these issues. Aiming at a higher signal-to-noise ratio, the focused source electromagnetic method and approaches of the differentially normalized method, first applied to petroleum exploration, are tested on a groundwater target, in a karst environment sectioned by a diabase dyke. We performed the processing and analysis on real IP resistivity profiling data acquired with two-way dipole-dipole array, guided by magnetic data acquired on the same profile, mapping a diabase dyke. The inversion of focused source electromagnetic method/differentially normalized method was not performed, instead that we converted the induced polarization–resistivity data to a differential signal to qualitatively prove the presence of aquifer. Joint interpretation of focused source electromagnetic method curves and inverted two-dimensional induced polarization–resistivity sections allowed for precise delineation of a conductive zone associated with the karst aquifer, le magnetics allowed for the definition of a neighbour dyke. The techniques have great potential in the aid of groundwater exploration, contributing substantially to the reduction of interpretation ambiguity. Focused source electromagnetic method/differentially normalized method/ approaches show that a simple linear combination of the conventional geoelectric data is able to remove the geological noise and provide the vertical focusing of the electric current. 相似文献
8.
The controlled‐source electromagnetic (CSEM) and magnetotelluric method (MT) are two techniques that can be jointly used to explore the resistivity structure of the earth. Such methods have, in recent years, been applied in marine environments to the exploration and appraisal of hydrocarbons. In many situations the electric properties of the earth are anisotropic, with differences between resistivity in the vertical direction typically much higher than those in the horizontal direction. In cases such as this, the two modes of the time‐harmonic electromagnetic field are altered in different ways, implying that the sensitivity to the earth resistivity may vary significantly from one particular resistivity component (scalar, horizontal or vertical) to another, depending on the measurement configuration (range, azimuth, frequency or water depth). In this paper, we examine the sensitivity of the electromagnetic field to a vertically anisotropic earth for a typical set of configurations, compare inversion results of synthetic data characterizing a vertically anisotropic earth obtained using the isotropic and anisotropic assumptions and show that correctly accounting for anisotropy can prevent artefacts in inversion results. 相似文献
9.
Electromagnetic signals from distant radio transmitters in the frequency range 15–250 kHz were measured to model an electrical resistivity structure beneath 7 profiles in the vicinity of the Karinu limestone quarry in Estonia with the aim to map the extent of the economically exploitable limestone. The resistivity models from a 2D inversion of determinant resistivity and phase values using an Occam type of regularization contained reasonably accurate information about the geometry, namely depth to the top and the bottom of the target high‐resistivity limestone. The resistivity models correlated well with existing geological evidences as well as information from closely located boreholes. However, the sharp lithological boundaries seen in the boreholes were not resolved exactly in the resistivity models. This is probably because of the smoothing regularization used in the inversion process. Combined use of borehole data together with resistivity models resulted in two major geological interpretations; a) towards the western part of the existing limestone quarry there is a NNW to NS striking fault, covered by post‐glacial sediments, b) a potential cost‐effective exploitable area containing high quality highly resistive limestone is located south of the existing quarry. This case study shows the applicability of the reasonably fast radio magnetotelluric (RMT) method for the exploration of near‐surface resources. 相似文献
10.
Accurate detection of damaged concrete zones plays an important role in selecting the proper remedial technique. This study presents results from an application of the electrical imaging method to monitor the development of cracks in fiber concrete beams.The study showed that resistivity measurements on the concrete specimens were able to detect the increase of concrete resistivity with the curing time that reached about 65 Ωm after 28 days of curing. A similar development trend of concrete compressive strength was also found.Two types of cracks were investigated, i.e., artificial cracks made of plastic sheets inserted in concrete and cracks developed during a four-step loading test. A mini-electric imaging survey with Wenner array was conducted on the tension face of the beams. To deal with the effect of the beam size new procedures to correct resistivity measurements before inversion were proposed and successfully applied in this study. The results indicated that both crack direction and depth could be accurately determined in the inverted resistivity sections. 相似文献
11.
唐山地区可液化场地标准CPT指标及其与剪切波速的关系 总被引：1，自引：0，他引：1
无论从以往大地震的经历还是未来潜在地震危险的角度,唐山地区都是一个研究液化的良好的实验场,对其可液化场地获取符合国际标准的、代表目前国际上液化势衡量指标发展趋势的CPT测试结果,对积累液化研究基础数据、研究液化前后场地的抗液化性能变化以及发展新的液化预测方法应是有意义的工作。本文采用国际标准的CPT技术对唐山地区可液化场地进行实地勘察测试,得到了锥尖阻力和侧壁摩阻力这两项新指标,提出了可液化场地剪切波速构造,同时利用系统的优势,得到了可液化场地锥尖阻力与剪切波速间的关系式,分析了可液化场地CPT剖面和剪切波速特征。几个方面的分析表明,给出的结果具有可靠性。 相似文献
12.
Dongdong Wang Yongxin Gao Cheng Yao Baozhen Wang Mengqiang Wang 《Geophysical Prospecting》2020,68(6):1958-1979
We investigate the seismoelectric/electroseismic wavefields excited by a point source in an air/seawater/three-layered porous medium configuration containing a hydrocarbon layer. The results show that if an explosive source for excitation is used, receivers at seafloor can record the coseismic electromagnetic fields accompanying the P, S, fluid acoustic waves and the interface responses converted from the acoustic waves at seafloor interface and from the seismic waves at the interfaces beneath the seafloor. Employing a vertical electric dipole source shows that, with the exception of the interface responses converted from electromagnetic waves at seafloor, the interface responses converted from transmitted electromagnetic waves at the interfaces beneath the seafloor can also be identified. Given that the strength of the explosive source is within excitation capability of industry air guns, the generated interface responses from the hydrocarbon layer can be detected by current electromagnetic sensors considering the low ambient noise at the seafloor. Our results demonstrate the feasibility of the seismoelectric method applied to marine hydrocarbon exploration. Electroseismic modelling results suggest that it is not practical to employ this method to prospect marine hydrocarbon layer due to the weak interface response signal, unless a much larger current is injected into seafloor. 相似文献
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14.
山东苍山地震前,新沂地震台电阻率有明显的中短期异常与之很好地对应,并有进入临震异常的标志。分析了电阻率的变化与苍山地震的对应性及预报概况。 相似文献
15.
İrfan Akca Thomas Günther Mike Müller‐Petke Ahmet T. Başokur Ugur Yaramanci 《Geophysical Prospecting》2014,62(2):364-376
Magnetic resonance sounding (MRS) has increasingly become an important method in hydrogeophysics because it allows for estimations of essential hydraulic properties such as porosity and hydraulic conductivity. A resistivity model is required for magnetic resonance sounding modelling and inversion. Therefore, joint interpretation or inversion is favourable to reduce the ambiguities that arise in separate magnetic resonance sounding and vertical electrical sounding (VES) inversions. A new method is suggested for the joint inversion of magnetic resonance sounding and vertical electrical sounding data. A one‐dimensional blocky model with varying layer thicknesses is used for the subsurface discretization. Instead of conventional derivative‐based inversion schemes that are strongly dependent on initial models, a global multi‐objective optimization scheme (a genetic algorithm [GA] in this case) is preferred to examine a set of possible solutions in a predefined search space. Multi‐objective joint optimization avoids the domination of one objective over the other without applying a weighting scheme. The outcome is a group of non‐dominated optimal solutions referred to as the Pareto‐optimal set. Tests conducted using synthetic data show that the multi‐objective joint optimization approximates the joint model parameters within the experimental error level and illustrates the range of trade‐off solutions, which is useful for understanding the consistency and conflicts between two models and objectives. Overall, the Levenberg‐Marquardt inversion of field data measured during a survey on a North Sea island presents similar solutions. However, the multi‐objective genetic algorithm method presents an efficient method for exploring the search space by producing a set of non‐dominated solutions. Borehole data were used to provide a verification of the inversion outcomes and indicate that the suggested genetic algorithm method is complementary for derivative‐based inversions. 相似文献
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17.
Erling Hugo Jensen Leiv‐J. Gelius Tor Arne Johansen Zhong Wang 《Geophysical Prospecting》2013,61(4):788-802
18.
Semi-empirical procedures for evaluating the liquefaction potential of saturated cohesionless soils during earthquakes are re-examined and revised relations for use in practice are recommended. The stress reduction factor (rd), earthquake magnitude scaling factor for cyclic stress ratios (MSF), overburden correction factor for cyclic stress ratios (Kσ), and the overburden normalization factor for penetration resistances (CN) are discussed and recently modified relations are presented. These modified relations are used in re-evaluations of the SPT and CPT case history databases. Based on these re-evaluations, revised SPT- and CPT-based liquefaction correlations are recommended for use in practice. In addition, shear wave velocity based procedures are briefly discussed. 相似文献
19.
河北阳原台地电阻率变化分析 总被引：5，自引：0，他引：5
河北阳原台地电阻率NE测向2014年以来出现年变幅变小的年变畸变现象,经核实,这时的观测系统工作正常,而降雨量与地电阻率的异常变化具有一定的相关性,但通过褶积滤波法去除降雨量的影响后,这种异常变化依旧存在。同时,阳原台NE测向的地电阻率与自然电位在2014年的变化具有同步性,也进一步验证了异常变化的可靠性。阳原台地电阻率观测位于晋冀蒙交界地区,对地壳的应力-应变响应比较敏感,其地电阻率异常变化与1989年大同地震和1998年张北地震有较好的对应关系,并显示出持续时间长、幅度大和恢复慢的特点。因此,阳原台地电阻率异常变化的可信度较高,可为监测晋冀蒙交界地区的地震活动提供参考。 相似文献
20.
Mauro Mele Silvia Inzoli Mauro Giudici Riccardo Bersezio 《Geophysical Prospecting》2014,62(3):631-645
Electrical conductivity of alluvial sediments depends on litho‐textural properties, fluid saturation and porewater conductivity. Therefore, for hydrostratigraphic applications of direct current resistivity methods in porous sedimentary aquifers, it can be useful to characterize the prevailing mechanisms of electrical conduction (electrolytic or shale conduction) according to the litho‐textural properties and to the porewater characteristics. An experimental device and a measurement protocol were developed and applied to collect data on eight samples of alluvial sediments from the Po plain (Northern Italy), characterized by different grain‐size distribution, and fully saturated with porewater of variable conductivity. The bulk electrical conductivities obtained with the laboratory tests were interpreted with a classical two‐component model, which requires the identification of the intrinsic conductivity of clay particles and the effective porosity for each sample, and with a three‐component model. The latter is based on the two endmember mechanisms, surface and electrolytic conduction, but takes into account also the interaction between dissolved ions in the pores and the fluid‐grain interface. The experimental data and their interpretation with the phenomenological models show that the volumetric ratio between coarse and fine grains is a simple but effective parameter to determine the electrical behaviour of clastic hydrofacies at the scale of the representative elementary volume. 相似文献