共查询到18条相似文献，搜索用时 460 毫秒
1.
地电阻率多极距观测中的最佳布极方式 总被引：2，自引：0，他引：2
对如何确定地电阻率多极距观测中的最佳布极方式, 包括极距个数和各极距长度的确定进行了研究。 确定最佳布极方式的主要依据是地下各层介质的响应系数随观测极距的变化规律以及采用不同观测极距对反演精度的影响。 以宝坻台为例, 讨论了在电性剖面参数已知的情况下, 如何确定多极距观测中各极距长度。 最后, 利用提出的最佳布极方式确定的装置系统对宝坻台模拟多极距观测资料进行了处理。 结果表明, 用最佳布极方式确定的多极距观测系统可精确计算出地下各层介质的真电阻率变化。 相似文献
2.
地电阻率多极距观测系统及试验研究 总被引：1，自引：0，他引：1
目前, 我国用于地震前兆监测的地电阻率观测系统大部分都是单一极距的, 这种观测方法在实际观测中普遍存在着地电阻率季节性变化的现象, 这种季节性变化与地震异常变化一起叠加在观测值中, 给地震异常的识别和判定带来了一定困难。 而解决这一问题的有效途径就是进行地电阻率的多极距观测。 本文介绍了采用ZD8MI电阻率多极距观测系统在山丹地震台的试验观测情况, 该系统是最新研制的、 专用于地震前兆监测的地电阻率多极距观测系统。 一年多的台站试验观测和反演结果表明, 浅层电阻率的变化相对较大, 而深层的相对变化较小, 因此利用多极距观测系统进行不同层位的地电阻率观测, 对排除干扰和识别地震前兆信息显得尤为重要, 是地电阻率观测技术发展的一个趋势。 相似文献
3.
四平台地电阻率相反年变有限元数值分析 总被引：5，自引：0，他引：5
本文依据吉林省四平台地质剖面、地下介质电性资料,将四平台地下介质电性分布简化为沿NW走向的二维电性结构,并结合台站电测深资料建立三维有限元模型,以模型浅层介质电阻率变化模拟测区浅层介质电阻率随季节的变化,计算了四平台N50°W和N40°E两测道地电阻率的年变化形态.计算结果表明,N50°W测道地电阻率在浅层介质电阻率升高时上升,在浅层介质电阻率降低时下降;N40°E测道地电阻率在浅层介质电阻率升高时下降,在浅层介质电阻率降低时升高.两测道地电阻率年变化表现出相反的形态,且N50°W测道年变幅度要大于N40°E测道,计算结果在变化形态上符合四平台实际的观测资料,因此认为四平台测区地下介质的非均匀分布是产生两测道地电阻率年变形态相反现象的原因. 相似文献
4.
地电阻率多极距观测的目的是借助对观测数据的反演获得地下介质中不同层位真电阻率的变化.本文以3层结构为例,对地电阻率多极距观测的一维反演的效果进行了初步地理论研究.首先研究了一维地电阻率结构下观测数据一维反演的模拟效果,得到了各层电阻率值,且与真电阻率值很接近,说明在地下电性结构为一维的情况下,电阻率多极距观测可以区分出不同地层的电阻率变化.其次,考虑到台址下电阻率结构的复杂性,研究了上两层界面存在起伏的情况下,多极距观测数据一维反演的效果,结果显示:当电阻率变化较小时,各层反演得到的电阻率的变化与真电阻率十分符合;当上两层介质的电阻率变化较大时,各层反演得到的电阻率出现畸变,与真实电阻率的变化情况存在一定差别,表明浅层电阻率变化达到一定程度后将会影响对深部电阻率变化情况的正确判断.一般情况下,观测的时间间隔越短,则连续两次观测时段内各层介质的电阻率变化越小,因此缩短多极距观测的时间间隔可能是避免出现上述畸变现象的有效观测手段. 相似文献
5.
晋冀蒙交界及附近地区小极距井下地电阻率观测装置设计 总被引：1，自引：1，他引：0
为提升2022年北京冬奥会期间地电阻率测项的震情保障能力,将对晋冀蒙交界及附近区域的宝昌、集宁、阳原、大同、代县、临汾、通州和平谷8个台站在原有观测基础上增加具有全空间性质的小极距井下地电阻率观测。本文根据台站钻孔岩芯剖面和电测深数据反演测区水平层状电性结构,利用介质对地电阻率观测的影响系数方法,计算影响系数随极距和埋深的变化,选择合适的极距和埋深,使浅层介质对地电阻率观测的影响尽可能小,使目标层位对观测的贡献尽可能大,减少浅层介质对观测的影响。由此得出了各台站观测极距及埋深等装置系数,在此基础上完成了8个台站观测装置的方案设计。 相似文献
6.
7.
8.
9.
10.
《地震地质》2016,(4)
在水平层状介质模型下,采用有限元数值计算方法建立三维模型,分析了地电阻率测区中位于地表的金属导线和局部电性异常体对观测产生的干扰形态和幅度随时间的变化特征。分析结果显示:1)低阻干扰源位于影响系数为正的区域时,将引起地电阻率观测值的下降变化,位于影响系数为负的区域时,将引起观测值的上升变化,高阻干扰源对观测的影响与之相反;2)地表干扰源影响的动态特征表现为,在浅层介质电阻率较低时对观测的干扰幅度要大于浅层介质电阻率较高时;3)对于正常年变的测道,低阻干扰源位于影响系数为正的区域时引起年变幅度增大,位于影响系数为负的区域时引起年变幅度减小,高阻干扰源对年变形态的影响与之相反;对于反常年变的测道,干扰源对年变形态的影响则与对正常年变测道的影响相反;4)金属导线对观测的干扰幅度受自身电阻率和横截面积影响:电阻率越低干扰幅度越大;有效横截面积越大干扰幅度越大。 相似文献
11.
APPARENT RESISTIVITY TEMPORAL VARIATION CHARAC-TERISTICS AFFECTED BY THE FIXED DISTURBANCE SOURCE ON SURFACE OF MEASURING AREA 
下载免费PDF全文
下载免费PDF全文 Current leakage,metallic conductor,and local anomalous resistivity body are main disturbance sources which affect the successive observation of apparent resistivity in stations,besides the observing system failure.We construct a finite element model using a 3-layered horizontal medium to discuss the dynamic characteristics of disturbances caused by metal conductor and local anomalous resistivity body in the measuring filed.The numerical results show that low resistivity source which is located in areas where the sensitivity coefficient is positive will cause decline on apparent resistivity observation.While low resistivity source will cause increase when it is located in areas where the sensitivity coefficient is negative.Disturbance caused by high resistivity source is opposite to the one from low resistivity source.The general dynamic feature of disturbance is that the disturbance amplitude increases as the resistivity of shallow layer decreases,while the amplitude declines when the shallow layer's resistivity increases.For the measuring direction which has normal annual variation form,low resistivity source which is located in area where the sensitivity coefficient is positive will increase the annual variation amplitude,while it will reduce annual amplitude when it is in a negative sensitivity coefficient area.Annual amplitude changes caused by high resistivity source are opposite to the changes caused by low resistivity source.For the measuring direction which has abnormal annual variation form,dynamic annual feature is opposite to the one in direction of normal annual variation form.If the dynamic feature is opposite to the annual variation and disturbance amplitude is also greater than annual amplitude,the annual variation will change direction.Disturbance amplitude from metallic conductor is affected by the resistivity and cross-section area,the lower of the resistivity and the larger of the cross-section area,the greater of the disturbance amplitude. 相似文献
12.
Parts of the consecutive apparent resistivity monitoring stations of China have recorded clear diurnal variations. The relative amplitudes of diurnal variations at these stations range from 1.3‰ to 5.8‰. The daily accuracies of apparent resistivity observation are better than 1‰, because the background electromagnetic noise is rather low at these stations. Therefore, the diurnal variations of apparent resistivity recorded at these stations are real phenomena. The diurnal variation shapes can be divided into two opposite types according to their characteristics. One type is that the apparent resistivity data decreases during the daytime but increases during the nighttime(Type 1). The other type is the apparent resistivity data increases during the daytime but decreases during the nighttime(Type 2). There is a correspondence between the diurnal and annual variation patterns of apparent resistivity. For the monitoring direction with diurnal variation of Type 1, the apparent resistivity decreases in summer and increases in winter. However, for the monitoring direction with diurnal variation of Type 2, the apparent resistivity increases in summer and decreases in winter.
We take an analysis on the mechanism of apparent resistivity diurnal variation, combining the influence factors of water-bearing medium's resistivity, the electric structure of stations, and the apparent resistivity sensitivity coefficient(SC)theory. Intuitively, diurnal variation of apparent resistivity is caused by diurnal variation of medium resistivity in the measured area. The diurnal variation of medium resistivity will inevitably be caused by the factors with diurnal variation. Among the possible factors, there is diural variation in earth tide and temperature.
Our analysis displays that apparent resistivity diurnal variation is not caused by the usually-believed earth tide, but by the ground temperature difference between daytime and nighttime. The earth tide strain is too small to cause remarkable effects on the apparent resistivity data. On the other hand, the daily tide strain has two peak-valley variations, and its phase and amplitude has a period of approximate 28 days. However, the apparent resistivity data do not show these corresponding features to earth tide. Furthermore, the detection range of current apparent resistivity stations is within a depth of several hundred meters. Within this depth range, the medium deformation caused by solid tide can be regarded as uniform change. Therefore, all monitoring directions and all stations will have the same pattern of diurnal variation.
In general, the temperature increases in the daytime but decreases in the nighttime. For most water-bearing rock and soil medium, its resistivity decreases as temperature increases and increases as temperature decreases. Diurnal temperature difference affects about 0.4m of soil depth. Therefore, resistivity of this surface thin soil layer decreases in the daytime while increases in the nighttime. Under layered medium model, SC of each layer represents its contribution to the apparent resistivity. For the stations with positive SC of surface layer, apparent resistivity decreases in the daytime but increases in the nighttime. While for the stations with negative SC of surface layer, apparent resistivity diurnal variations display the opposite shape. 相似文献
13.
甘肃大地电场的变化特征分析 总被引：1，自引：0，他引：1
对甘肃省平凉、松山、古丰、山丹、高台、嘉峪关、瓜州7个台站的地电场分钟值、小时值的日变特征进行了对比,对2012年3月地电场小时值进行了频谱分析,同时结合地磁场H分量、分量应变(固体潮)进行了对比分析。结果表明:1地电场静日的日变化都很明显,呈明显"双峰"和"单谷"形态,并且NS向与EW向变化形态基本相同;各台站同测向及相互之间的自相关系数基本在0.85;不同台站之间同测向的相关系数多数在0.75以上;这是地磁场H分量与固体潮共同影响的结果。2通过频谱分析各台站的优势周期主要以12h和8h为主,但存在差异性,谱值最大相差20倍。3各台站的日变幅也不尽相同,其中,差异性主要表现为与地磁场和固体潮影响量的差异性,并与台站的位置、地质构造、电性结构、浅层电阻率等有很大关系。 相似文献
14.
井下地电阻率观测影响系数分析——以江宁地震台为例 总被引：3，自引：2，他引：1
采用水平层状均匀介质中点电源位于任意深度时的电位解析表达式,以江宁台3层电性结构为例,分析了井下对称四极地电阻率观测时各层影响系数随深度、极距的变化,并结合探测深度探讨了实施井下观测时影响系数在选择供电极距和电极埋深时的作用。结果表明,对于"K"型电性结构,江宁台井下观测对地表、浅层干扰有较强的抑制作用,其短极距观测对地表、浅层干扰的抑制能力显著优于长极距观测;长极距观测在电极埋深H小于100m时对地表介质季节性的干扰具有放大作用;浅层影响系数一定时,电极埋深和供电极距需同时增加;江宁台井下观测供电极距AB/2取100～150m、电极埋深H为250m较为合理。 相似文献
15.
16.
Four types of disturbances in the seasonal variation in georesistivity are presented in the light of specific circumstances
in China. As the results of theoretic calculation for the models and in comparison of the calculated results with the seasonal
variations observed at 40 georesistivity stations, the following points are found: (1) The seasonal variation in georesistivity
is caused by the change in resistivity of the surface layer, especially by the annual variation of phreatic level when the
sounding depth is too shallow. This is one of the disturbances and thus has no relation to the origin of earthquake. The feature
and amplitude of the seasonal variation depend on the types of disturbance models, geoelectric cross sections and sounding
depth. (2) The seasonal variation in georesistivity usually has the same sign as that of the change in resistivity of shallow
layer and thus the normal seasonal change appears. However, as far as the K or Q types of geoelectric cross sections are concerned,
the abnormal seasonal variation in georesistivity starts to appear with a certain electrode spacing, when the interference
layer is located in the first layer. (3) Both abnormal and normal seasonal variations in georesistivity will be smaller than
2% when the sounding depth is greater than 300 m. Therefore, the seasonal variations can be removed or restrained when the
location of observation has been properly chosen or the electrode spacing is enlarged enough to obtain a sufficient sounding
depth. 相似文献
17.
本文评价了四川汶川MS8.0、芦山MS7.0地震前后成都台地电观测环境,研究了该台视电阻率变化.结果为:(1)两次大震发生在该台以西的龙门山断裂带、震源机制和震源深度接近,是近距离大震,相应地,在两次地震前该台两个正交测道中的每一测道视电阻率变化均显示了中期异常及其变化过程的重现性和异常幅度的相似性;(2)在每次地震前,两个测道表现了异常变化形态、幅度和起始时间的差异性.其重现性、相似性证明这些异常与两次大震晚期孕育有关;差异性主要展示了与震源机制有直接联系的视电阻率各向异性变化,揭示了震前该台地下介质经历了强烈的电性各向异性变化的过程. 相似文献