Abstract: Three times of magnetotelluric measurements were carried out during loading and unloading of the Longtan reservoir in Guangxi Zhuang Autonomous Region from 2009 to early 2010.The surveys were conducted at 4 sites with a frequency band 320Hz～1000s.The observational results show that the electricity of deep subsurface changed in different manners during the loading and unloading of the reservoir,depending on the specific structures and rock properties.At the 3 sites where the exposed rocks are of same lithology,the measured electric resistivity exhibited considerable variations at the band less than 1Hz.When the water level was the highest,the apparent resistivity was the lowest.As the water was declining,the apparent resistivity reached the maximum.And this value was the intermediate when the water level was the lowest.These measurements indicate that at different stages of loading and unloading of the reservoir,the rock properties,area of the reservoir and change of reservoir weight can pose a major influence on interconnection and seepage of underground water,causing variations of electricity of the subsurface at a certain depth.

Key words: Longtan reservoir of Guangxi, loading and unloading of reservoir, magnetotelluric measurement, apparent resistivity

摘要： 在广西龙滩库区于2009年至2010年初库水加卸载过程中,对4个测点进行了3期次大地电磁观测,观测频段为320Hz～1000s。观测结果显示库水加卸载过程中深部介质电阻率变化与岩性有关。在同一岩性出露区域的3个测点,库水加卸载的3期次观测的视电阻率数值在频率<1Hz以下频段变化明显,库水水位最高时段测量的视电阻率值最低,水位下降阶段测量的视电阻率数值最高,最低水位测量的视电阻率数值居中。实测结果表明:在广西水库水位加卸载过程的不同时段,库区岩性、库容面积和自重变化对地下水的连通和渗透有较大影响,从而导致地下一定深度下的介质电性发生变化。

关键词: 广西龙滩水库, 库水加卸载, 大地电磁测量, 视电阻率值