共查询到19条相似文献,搜索用时 375 毫秒
1.
2.
3.
对井下地电阻率观测的探测深度进行了研究,计算了均匀半空间和给定结构参数的水平层状介质模型在不同装置电极埋深下的探测深度,分析了探测深度与装置电极埋深和介质电阻率结构之间的关系,得到如下结果:①与地表观测相比,在供电极距为1 km左右时,探测深度随装置电极埋深的增大而增大,且增大的速度与装置电极埋深密切相关;当装置电极埋深h < 100 m时,探测深度的增大速度远小于装置电极埋深h≥100 m时. ②当装置电极埋深h < 50 m时,与地表观测相比探测深度增加很小,不超过10 m;当装置电极埋深相同时,供电极距越大,与地表观测相比探测深度增加得越小. ③对于水平层状电阻率均匀分层结构,在装置电极埋深相同的情况下,下伏低阻结构的探测深度显著大于下伏高阻结构.本文的研究结果表明,为了观测到深部电阻率的变化情况,首先需要查明测区电性结构,再进行综合分析,以确定井下地电阻率观测的装置电极埋深,其结果为深部电阻率变化研究提供了理论基础. 相似文献
4.
5.
2020年7月12日唐山古冶 MS5.1地震发生前,井下小极距地电阻率出现快速下降-折返的变化,变化形态、异常时长符合地电阻率孕震机理变化,但下降幅度远远小于地表大极距地电阻率孕震过程的变化幅度.因此,文章基于通州台地下电性结构和装置系统,采用数值分析方法,分析地表和井下小极距地电阻率的探测深度.结果表明,当底层电性变化区域介质电阻率发生某种减小时,通州台地表和井下小极距地电阻率装置系统地电阻率观测值会下降,下降的幅度随着深部介质电阻率变化区域上界面向上的扩展而增大.相比地表观测,井下小极距电阻率观测能更显著地接收到深部电阻率变化信号,对孕震有更强的反映能力. 相似文献
6.
地震地电阻率是观测中强地震孕震过程中微变形或微破裂变化的方法之一。近年来发展起来的小极距井下地电阻率观测,不仅能够抑制地表环境干扰,还能够缓解地表地电阻率占地面积大的困扰。基于北京地区延庆台、平谷台和通州台小极距井下地电阻率观测,通过与同场地地表地电阻率对比观测和数值模拟计算,分析了地表铁质干扰、季节变化、降水和潜水等因素对地电阻率观测的影响。结果显示,与同场地地表地电阻率相比,小极距井下地电阻率对地表自然环境因素的影响有较好的抑制能力,增强了观测效能。 相似文献
7.
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
8.
《地球物理学进展》2016,(5)
天水地震台井下地电观测与常规的地面观测相比,减少干扰、提高信噪比,在近三年的地电阻率观测中,观测精度无超过0.5%数据,数据的内在质量较好.2013年4月10日开始,NS、EW道井下(100 m)观测的地电阻率出现了波动变化,持续11天后距该台550 km的四川芦山发生了M_S7.0级地震,5月4号芦山地震余震相对减少后,地电阻率资料的波动变化也同步终止;2013年6月11日18时开始,天水台地电阻率再次出现异常波动变化,7月22日距该台156 km发生岷县-漳县M_S6.6级地震.采用天水地电台井下不同时段(凌晨2点和全天)和不同深度(6 m和100 m电极)观测的地电阻率数据对比分析这两次地震前后地下介质的电性变化,深部记录到明显的异常变化;用小波(db4)分解发现在芦山M_S7.0和岷漳M_S6.6级地震前视电阻率的细节部分的形态是连续的振荡,尺度部分出现了趋势性似"漏斗"变化形态,与过去强震震例形态具有相似性、重复性.深井地电观测技术的应用,减小了地面离散电流影响,直接观测探测层介质的电性变化,是探索预报地震的新思路、新方法. 相似文献
9.
10.
为压制地电阻率浅层干扰、突出深部以地震预报为目的的有用信息,选取了小江断裂中段一个场点作为实例,研究了井下地电阻率前兆观测中确定电极埋深、电极间距等布极参数的方法。结果表明:选择井下电阻率观测布极参数时要考虑影响系数和探测深度2个主要因素,即地下潜水位面以上各地层的影响系数应远小于深部各层,探测深度范围内最底层(受孕震影响最大的层)的影响系数应远大于其它各层,观测系统的探测深度最好不小于已有震例指示的地电阻率观测系统的探测深度。按照该方法选择了所给场点的井下电阻率观测布极参数,即电极埋深200 m、供电极距1 050 m、测量极距350 m,按对称四极布置,可获得最佳观测效果。 相似文献
11.
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
12.
本文基于测深反演结果, 通过数值模拟定性分析了地下水位和降雨对周至地电台地电阻率观测的影响; 同时利用褶积算法定量分析了降雨对该台NS向和NE向地电阻率观测的短期影响和长趋势影响.结果表明, 周至地电台地电阻率年变主要由地表薄层介质电阻率季节变化引起, 受地下水位变化影响不明显. 降雨对NS向和NE向地电阻率观测值的影响在短期内与观测结果一致, 表现为增加; 但长期趋势则与观测结果呈负相关关系.根据数值模拟分析认为, 这种变化与降雨及其渗透深度有关.分析结果与实际观测结果一致, 为正确认识周至地电台地电阻率观测与异常判定提供合理的理论依据. 相似文献
13.
14.
15.
16.
The temporal variation in a soil moisture profile can be studied using resistivity sounding data acquired at different times. The layered earth model based estimation of soil moisture from apparent resistivity data is a two-step non-linear inversion. Firstly, the apparent resistivity data are inverted to derive the layer resistivity variations and thicknesses and, secondly, the moisture content is estimated from these layer resistivity variations using a calibration equation. The soil moisture–resistivity problem was studied using the one-dimensional formulation of resistivity problem. A generalized geoelectric earth model was considered to simulate the soil moisture distribution and its temporal variation in the unsaturated zone. An algorithm (RESMOS) for the interpretation of the apparent resistivity data in terms of soil moisture variations through this two-step inversion process is reported. 相似文献
17.
针对我国地震监测预报中地电阻率定点连续观测中存在的偶极接地线的干扰问题, 本文将台站区域地层简化为3层均匀介质模型, 将接地线等效为偶极接地的电阻体, 建立了接地线干扰地电阻率观测的耦合物理模型. 通过有限元分析软件ANSYS模拟分析不同电性断面情况下接地线对地电阻率观测的影响, 同时分析这种干扰的产生机理, 并结合实际观测中存在的干扰问题作了对比验证分析. 结果表明: ① 接地线使得供电电极产生的地下对称性电场分布发生局部调整, 从而影响地电阻率观测; ② 接地线对地电阻率观测的影响主要取决于线缆的位置及方位角的大小; ③ 适当增大电极埋深可以减小其对地电阻率观测的影响; ④ 电性结构的差异性决定干扰变化幅度的大小. 本文结果对相关台站地电阻率观测异常分析落实及干扰源避让和观测系统改造具有参考意义. 相似文献
18.
APPARENT RESISTIVITY TEMPORAL VARIATION CHARAC-TERISTICS AFFECTED BY THE FIXED DISTURBANCE SOURCE ON SURFACE OF MEASURING AREA 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