地电阻率与水位关系的机理分析

从地电阻率的观测理论出发, 指出地电阻率场地的电性结构、 岩石的饱和度和孔隙度决定了地电阻率和水位的关系。 在长期的观测资料基础上, 通过实例系统地分析了地电阻率和水位的关系, 给出了不同层位的水位变化和不同方式的水位变化对地电阻率观测结果的影响, 认为非构造水位变化与地电阻率的关系主要取决于表层土壤或岩石的水饱和度, 构造水位变化与地电阻率变化存在明确的相关关系, 从而进一步探讨了与前兆异常有关的水位和地电阻率变化。     

中尺度模拟土壤油污染区探地雷达探测效果分析

为使物理模拟实验效果与实际探测情形更为接近,在室外自然条件下建立中尺度土壤石油污染实验模型,油污染区扩展深度超过1 m,采用实地探测中常用的500 MHz雷达天线进行长期定时探测.通过实测雷达图像特征、土壤含水量含油量分析,并对比前人开展的小尺度室内模拟试验结果,综合评价探地雷达对油污染区的探测效果.研究表明探地雷达探测图像异常特征与污染区扩散阶段密切相关:包气带内油污染区会引起振幅增强;毛细带的油污染区则表现为水位面反射轴附近清晰可辨的高幅异常区,且水位面反射轴呈下凹状;随扩散过程持续进行,异常区下移与水位面反射轴相交,并产生水平扩张.当污染土含油饱和度大于20%时,可通过雷达图像异常区圈定污染范围;当污染土含油饱和度大于15%时,可通过频谱图出现低频响应的位置圈定污染区水平范围.中尺度实验结果与室内小尺度模拟结果具有一致性,可作为油污染区雷达图像异常的解译依据.     

山西离石中心地震台洞体形变观测异常分析

通过对离石中心地震台洞体形变近6年观测资料中典型异常形态及与其相关地震的对应关系进行分析,结果表明,异常形态主要表现为短期趋势转折,突跳、毛刺、加粗等的数据波动,固体潮畸变伴掉格,且大多数异常是3种形态的组合;多数异常在震前发生,震后迅速恢复,固体潮分钟值曲线上有同步变化;水平摆和伸缩仪对应国内外6级以上的地震出现不同程度的异常反映,水管仪表现不明显。     

合肥台地电阻率NS向趋势异常变化原因分析

合肥台NS测向地电阻率自2015年以来出现趋势下降异常,经核实2015—2016年降雨量增多和地下水位抬升与地电阻率趋势下降异常变化显著相关。通过褶积滤波法和相关分析法分别消除降雨和水位影响后,趋势下降变化不明显,从而认为此变化为干扰所致,非地震前兆异常,并探讨了这种干扰影响机制,为今后判断引起地电测值变化的原因提供了科学依据。     

三维井地磁测联合约束反演

井中磁测在铁矿等磁性金属矿床勘查中具有举足轻重的作用.针对磁性金属矿床深部资源勘查中存在的有效信号弱、矿体形态复杂等技术难题,本文利用井中三分量磁测资料和地面磁测资料直接反演地下空间磁化率的分布情况,充分发挥纵、横向分辨率高的优势,通过磁化率的变化来确定矿（化）体的范围.分析了磁化率和磁场H_ax、H_ay、Z_a、ΔT各参量之间的关系,导出了磁化率反演方程;将钻孔编录、磁化率测井等结果作为约束条件构建了目标函数.以组合倾斜板状体模型为例,验证了方法的有效性,并在青海野马泉铁多金属矿区开展应用试验,试验结果与已有地质资料基本一致.该方法有效抑制了因反演数据源单一、缺乏约束条件而造成反演结果的多解性,实现了磁测资料的精细反演解释,为查明地下矿体空间位置、形态及规模,提高找矿效果,提供了一种新的解决方案.     

Gaussian mixture–based equivalent linearization method (GM-ELM) for fragility analysis of structures under nonstationary excitations

Gaussian mixture–based equivalent linearization method (GM-ELM) is a recently developed stochastic dynamic analysis approach which approximates the random response of a nonlinear structure by collective responses of equivalent linear oscillators. The Gaussian mixture model is employed to achieve an equivalence in terms of the probability density function (PDF) through the superposition of the response PDFs of the equivalent linear system. This new concept of linearization helps achieve a high level of estimation accuracy for nonlinear responses, but has revealed some limitations: (1) dependency of the equivalent linear systems on ground motion intensity and (2) requirements for stationary condition. To overcome these technical challenges and promote applications of GM-ELM to earthquake engineering practice, an efficient GM-ELM-based fragility analysis method is proposed for nonstationary excitations. To this end, this paper develops the concept of universal equivalent linear system that can estimate the stochastic responses for a range of seismic intensities through an intensity-augmented version of GM-ELM. Moreover, the GM-ELM framework is extended to identify equivalent linear oscillators that could capture the temporal average behavior of nonstationary responses. The proposed extensions generalize expressions and philosophies of the existing response combination formulations of GM-ELM to facilitate efficient fragility analysis for nonstationary excitations. The proposed methods are demonstrated by numerical examples using realistic ground motions, including design code–conforming nonstationary ground motions.     

All pixels are useful,but some are more useful: Efficient in situ data collection for crop-type mapping using sequential exploration methods

A precise knowledge of the crop distribution in the landscape is crucial for the agricultural sector to inform better management and logistics. Crop-type maps are often derived by the supervised classification of satellite imagery using machine learning models. The choice of data sampled during the data collection phase of building a classification model has a tremendous impact on a model's performance, and is usually collected via roadside surveys throughout the area of interest. However, the large spatial extent, and the varying accessibility to fields, often makes the acquisition of appropriate training data sets difficult. As such, in situ data are often collected on a best-effort basis, leading to inefficiencies, sub-optimal accuracies, and unnecessarily large sample sizes. This highlights the need for new more efficient tools to guide data collection. Here, we address three tasks that one commonly faces when planning to collect in situ data: which survey route to select among a set logistically feasible routes; which fields are the most relevant to collect along the chosen survey route; and how to best augment existing in situ data sets with additional observations. Our findings show that the normalised Moran's I index is a useful indicator for choosing the survey route, and that sequential exploration methods can identify the most important fields to survey on that route. The provided recommendations are flexible, overcome the main logistical constraints associated with in situ data collection, yield accurate results, and could be incorporated in a mobile application to assist data collection in real-time.     

地网对VHF天线性能影响的分析研究

基于VHF频段射电天文干涉阵列的天线,研究地网以及不同环境对天线辐射特性包括增益、方向图、谐振点等参数的影响。结果表明,无地网条件下,天线在干燥土壤和沙地的增益分别是3.06 dB和1.44 dB,且存在明显的旁瓣和后瓣;天线在潮湿土壤和沙地的增益分别是4.33 dB和4.25 dB。增加地网后,天线在干燥土壤和沙地的增益分别是4.87 dB和4.97 dB,潮湿土壤和沙地分别是4.39 dB和4.40 dB,方向图不存在明显的后瓣和旁瓣,谐振点稳定在27.0 MHz和69.5 MHz处,且在此之间的频段上,驻波比均满足银河噪声限制条件。由此可以得出结论:在干燥土壤和沙地上铺设地网时,VHF天线性能最好,噪声最低,这对大规模的VHF天线阵列的基础构建环境选择至关重要。     

广饶县地面沉降成因及预测分析

地面沉降是指由于自然因素或人类工程活动引发的地下松散岩层固结压缩,并导致一定区域范围内地面高程降低的地质现象,是一种缓变性地质灾害。广饶县地处东营市南端,根据2004—2016年地面沉降监测资料,其沉降中心累计沉降量已超过了1 500mm,最大沉降速率超过70mm/a,属地面沉降强发育。通过对地面沉降发生、发展规律和引发地面沉降的成因进行了分析,并在现状条件下对地面沉降趋势进行了预测分析。     

探地雷达应用概述

以ASTM标准规范为基础对探地雷达（Ground Penetrating Radar 以下简称GPR）的地下探测方法的应用做了比较系统的概述,主要内容包括：部分专业术语的解释;测试过程中雷达探测深度及其中心频率、垂直分辨率、水平分辨率等的关系,测试过程中常见的天线移动方式,以及雷达波速的预测几种方法,数据显示方式;雷达数据解释和数据处理的一般过程及方法.目前我国尚没有关于GPR的国家规范或行业标准,文章对GPR的使用及规范的编制具有一定的参考意义.