Spatial-temporal Variations of H2 Concentration in Soil Gas in the Seismic Fault Zone Produced by the Wenchuan MS 8.0 Earthquake     

Zhou Xiaocheng  Shi Hongyu  Chen Chao  Zeng Linghua  Sun Fengxia  Li Jing  Chen Zhi  Lü  Chaojia  Huang Dan  Du Jianguo 《地球科学进展》2017,32(8):818-827

Degassing of Hydrogen (H₂) from fault may be a good indicator of fault activity. The concentration of H₂ in soil gas in the seismic surface rupture zone produced by the Wenchuan M_S 8.0 earthquake was investigated in twenty three measuring regions in order to explore the relationship between the spatio-temporal variations of H₂ concentration in soil gas along the seismic rupture zone and the vertical displacements and aftershocks activities. The results indicated: ① the sources of H₂ were directly related to from the release of natural gas reservoirs; ②the average concentration of H₂ in soil gas spatially decreased from Yingxiu to Nanba; ③the magnitudes of the H₂ concentration anomalies declined significantly with time. It is very significant to study the variation tendency of atmospheric environment with further research of degassing of H₂ from faults.  相似文献   

土壤地球化学测量在文登青庄地区金矿勘查中的应用          下载免费PDF全文

张朋朋 《山东国土资源》2017,33(4)

为有效、准确的寻找金矿床,结合文登青庄地区基岩出露情况,选择开展了1∶1万土壤地球化学测量。该次工作测网选择100 m×40 m,局部加密至100 m×20 m,采集20~30 cm深处的BC层土壤,过40目样筛,过筛后样品重量均大于150 g,分析Au,Ag,Cu,Pb,Zn,As,Bi,Mo等8种元素。通过对各元素分析结果进行R型聚类分析,认为将As,Sb元素作为寻找Au矿的主要指示元素在该区不适用,该区Au与Bi的相关性较好。通过合理确定各元素的背景值和异常下限,圈定单元素异常190处,根据元素组合特征圈定综合异常19处,其中AP7,AP19成矿条件较好,划分为乙1类异常,重点开展异常查证工作。通过探槽施工、化验分析等异常查证工作,在两个异常内均发现金矿(化)体,样品中金品位(0.30~3.64)×10-6,确定了土壤地球化学测量在该区找矿工作中的适用性和有效性。区内发现的金(矿)化体赋存于蚀变破碎带内,矿化蚀变主要有黄铁矿化、硅化、绿泥石化,与邻近的西院下金矿相似,初步确定区内寻找的金矿床类型应为构造角砾岩-碎裂岩型金矿床。  相似文献   

Estimating soil moisture using remote sensing data: A machine learning approach   总被引：4，自引：0，他引：4  

Sajjad Ahmad  Ajay KalraHaroon Stephen 《Advances in water resources》2010

Soil moisture is an integral quantity in hydrology that represents the average conditions in a finite volume of soil. In this paper, a novel regression technique called Support Vector Machine (SVM) is presented and applied to soil moisture estimation using remote sensing data. SVM is based on statistical learning theory that uses a hypothesis space of linear functions based on Kernel approach. SVM has been used to predict a quantity forward in time based on training from past data. The strength of SVM lies in minimizing the empirical classification error and maximizing the geometric margin by solving inverse problem. SVM model is applied to 10 sites for soil moisture estimation in the Lower Colorado River Basin (LCRB) in the western United States. The sites comprise low to dense vegetation. Remote sensing data that includes backscatter and incidence angle from Tropical Rainfall Measuring Mission (TRMM), and Normalized Difference Vegetation Index (NDVI) from Advanced Very High Resolution Radiometer (AVHRR) are used to estimate soil water content (SM). Simulated SM (%) time series for the study sites are available from the Variable Infiltration Capacity Three Layer (VIC) model for top 10 cm layer of soil for the years 1998–2005. SVM model is trained on 5 years of data, i.e. 1998–2002 and tested on 3 years of data, i.e. 2003–2005. Two models are developed to evaluate the strength of SVM modeling in estimating soil moisture. In model I, training and testing are done on six sites, this results in six separate SVM models – one for each site. Model II comprises of two subparts: (a) data from all six sites used in model I is combined and a single SVM model is developed and tested on same sites and (b) a single model is developed using data from six sites (same as model II-A) but this model is tested on four separate sites not used to train the model. Model I shows satisfactory results, and the SM estimates are in good agreement with the estimates from VIC model. The SM estimate correlation coefficients range from 0.34 to 0.77 with RMSE less than 2% at all the selected sites. A probabilistic absolute error between the VIC SM and modeled SM is computed for all models. For model I, the results indicate that 80% of the SM estimates have an absolute error of less than 5%, whereas for model II-A and II-B, 80% and 60% of the SM estimates have an error less than 10% and 15%, respectively. SVM model is also trained and tested for measured soil moisture in the LCRB. Results with RMSE, MAE and R of 2.01, 1.97, and 0.57, respectively show that the SVM model is able to capture the variability in measured soil moisture. Results from the SVM modeling are compared with the estimates obtained from feed forward-back propagation Artificial Neural Network model (ANN) and Multivariate Linear Regression model (MLR); and show that SVM model performs better for soil moisture estimation than ANN and MLR models.  相似文献   

Three-dimensional simulation of track on poroelastic half-space vibrations due to a moving point load   总被引：1，自引：0，他引：1  

Honglei Sun  Yuanqiang Cai  Changjie Xu 《Soil Dynamics and Earthquake Engineering》2010

An analytical approach is used to investigate dynamic responses of a track system and the poroelastic half-space soil medium subjected to a moving point load under three-dimensional condition. The whole system is divided into two separately formulated substructures, the track sub-system and the ground. The ballast supporting rails and sleepers is placed on the surface of the ground. The rail is modeled by introducing the Green function for an infinitely long Euler beam subjected to the action of the moving point load and the reaction of sleepers represented by a continuous mass. Using the double Fourier transform, the governing equations of motion are then solved analytically in the frequency–wave-number domain. The time domain responses are evaluated by the inverse Fourier transform computation for a certain load velocities. Computed results show that dynamic responses of the soil medium are considerably affected by the fluid phase as well as the load velocity.  相似文献   

People’s perception and socioeconomic determinants of soil erosion:A case study of Samanalawewa watershed,Sri Lanka   总被引：3，自引：0，他引：3  

E.P.N. UDAYAKUMARA  R.P.SHRESTHA  L.SAMARAKOON  D.SCHMIDT-VOGT 《国际泥沙研究》2010,25(4):323-339

Though soil erosion is an important concern in Sri Lanka, there is a dearth of baseline information on soil erosion in many ofits watersheds, which obstructs monitoring of soil erosion and mitigating its effects. In order to assess soil erosion in a critical watershed and to identify its determinants, the Samanalawewa watershed, which contains one of the main hydropower generating reservoirs in Sri Lanka, was selected for this study. Remote-sensing (RS) and geographic information system (GIS) based modeling...  相似文献   

Response of circular flexible foundations subjected to horizontal and rocking motions     

《Soil Dynamics and Earthquake Engineering》2015

A methodology using modal analysis is developed to evaluate dynamic vertical displacements of a circular flexible foundation resting on soil media subjected to horizontal and rocking motions. The influence of the soil reaction forces on the foundation is considered by introducing modal impedance functions, which can be determined by an efficient procedure with ring elements. The displacements of the foundation can then be easily solved by modal superposition. Parametric studies for modal responses of the flexible foundation indicate that the coupled response of the foundation is significantly influenced by relative stiffness among the foundation and the soil medium, vibration frequency range, foundation mass, and boundary contact conditions. The welded boundary condition should be considered to predict the coupling response while the relaxed boundary condition may be used to predict approximately the vertical displacements. As a foundation with a relative stiffness ratio more than three, it is found that the foundation can be considered as rigid to calculate coupling displacements. For a slightly flexible foundation, considerations of three modes are sufficient enough to obtain accurate foundation responses. Moreover, at low frequencies, the coupling effect due to higher mode can be neglected.  相似文献   

General formulation and solution procedure for harmonic response of rigid foundation on isotropic as well as anisotropic multilayered half-space     

《Soil Dynamics and Earthquake Engineering》2015

A general formulation and solution procedure are proposed for harmonic response of rigid foundation on multilayered half-space. It is suitable for isotropic as well as anisotropic soil medium. The wave motion equation is formulated in frequency wave-number domain in the state space. A hybrid approach is proposed for its solution, where the precise integration algorithm (PIA) is employed to carry out the integration. Very high accuracy can be achieved. The mixed variable form of wave motion equation enables the assembly of layers simple and convenient. The surface Green׳s function is regarded as rigorous, because it is free from approximations and discretization errors. The algorithm is unconditionally stable. The numerical implementation is based on algebraic matrix operation. Numerical examples of vibration of rigid foundation validate the efficiency and accuracy of the proposed approach.  相似文献   

Mitigation of seismic settlement of light surface structures by installation of sheet-pile walls around the foundation     

《Soil Dynamics and Earthquake Engineering》2015

Settlement of surface structures, which is particularly a private house, due to subsoil liquefaction is not a new issue in geotechnical engineering. It has been happening during earthquakes in liquefaction-prone areas since many years ago. However, to date no reliable measure against this problem with reasonable cost has been proposed to people. In this paper, results of a series of 1-g shaking table tests which have been conducted to evaluate performance of a possible mitigation against this problem are presented. The proposed mitigation herein is installation of sheet-pile walls around the foundation. In order to reduce the cost of mitigation, sheet-piling with gap and half-length sheet-piling were examined. The experiments were conducted in different ground water levels. It is found out that installing sheet-pile walls in relatively low ground water level can stop settlement of structures completely. Sheet-piling with gaps delays initiation of settlement but it may increase the ultimate settlement of structure. In addition, it is found that formation of a water film under the building׳s foundation is the governing mechanism of post-shaking settlement of structures.  相似文献   

Mechanism and bounding of earthquake energy input to building structure on surface ground subjected to engineering bedrock motion     

《Soil Dynamics and Earthquake Engineering》2015

The mechanism of earthquake energy input to building structures is clarified by considering the surface ground amplification and soil–structure interaction. The earthquake input energies to superstructures, soil–foundation systems and total swaying–rocking system are obtained by taking the corresponding appropriate free bodies into account and defining the energy transfer functions. It has been made clear that, when the ground surface motion is white, the input energy to the swaying–rocking model is constant regardless of the soil property (input energy constant property). The upper bound of earthquake input energy to the swaying–rocking model is derived for the model including the surface ground amplification by taking full advantage of the above-mentioned input energy constant property and introducing the envelope function for the transfer function of the surface ground amplification. Extension of the theory to a general earthquake ground motion model at the engineering bedrock is also made by taking full advantage of the above-mentioned input energy constant property.  相似文献   

Seismic response of high plasticity clays during extreme events     

《Soil Dynamics and Earthquake Engineering》2015

Mexico City high plasticity clays exhibit a small degree of nonlinearity for shear strains as large as 0.1%, which leads to both moderate shear stiffness degradation and small to medium damping increment, even for long duration subduction strong ground motions, such as the 8.1M_w 1985Michoacan earthquake. Nonetheless, current seismic design criteria of strategic infrastructure used worldwide have striven for having larger return periods for establishing the seismic environment, considering recent large magnitude (M>8.5M_w) events. This paper presents the study of the seismic response of typical high plasticity clays found in the so-called Texcoco Lake, in the surrounding of Mexico City valley, for larger to extreme earthquakes. The shear wave velocity profile was characterized using a down-hole test. The seismic environment was established from a set of uniform hazard response spectra developed for a nearby rock outcrop for return periods of 125, 250, 475 and 2475 years. A time-domain spectral matching was used to develop acceleration time histories compatible with each uniform hazard response spectrum. Both frequency and time domain site response analyses were carried out considering each seismic scenario. Ground nonlinearities were clearly observed in the soil response during extreme ground shaken, which increases rapidly with the return period. This fact must be taken into account to avoid costly and potentially unsafe seismic designs.  相似文献