Abstract: Based on the synchronized observation data of 1s sampling rate Network MT(N-MT)system with FHDZ-M15 geo-magnetometer installed at Jinghai seismic observatory in the "Tenth Five-Year Program" period,we carried out the MT measurement at a stationary station. Robust technology was employed in data processing to the data recorded at Jinghai observatory from January to June,2008. The tensor impedances were obtained. The temporal abnormal change of 18 apparent resistivity and impedance phases of same-period in the range of periods of 6～600s was analyzed. The results show there exist changes in some periods of apparent resistivity and impedance phases before the M_L 4.2 Lulong earthquake on March 17,2008. In this study,the period of data used corresponds to the depth of 5～ 50km,a range of focal depth of North China. The result indicates the change of electrical conductivity of the strata in the source area before and after the earthquake. The MT method can reflect the electrical conductivity changes at the source area more directly than the existing geoelectric observation methods,and it has bigger advantage for deeper exploration.

Key words: electromagnetic filed, MT, apparent resistivity, phase, earthquake precursor, Jinghai Observatory

摘要： 文中利用"十.五"期间静海地震台布设的秒采样大地电磁网(N-MT)仪器系统和FHDZ-M15地磁组合系统的同步观测数据,实现了固定台站大地电磁测深(MT)观测。采用Robust技术对静海地震台2008年1—6月记录的天然电磁场观测数据进行了MT处理,得到了张量阻抗资料。经过对周期为6～600s范围的18个相同周期的视电阻率及阻抗相位随时间的变化进行分析,其中有多个周期的视电阻率及阻抗相位的时序曲线在2008年3月11日卢龙M_L4.2地震前出现异常变化。研究使用的资料周期对应深度为5～50km,属华北地震震源深度范围,其结果反映了震源区地层地震前后震源深度的电性变化。MT方法比现行的地电观测方法具有更直接反映震源区地层的电性变化和更深的勘探深度的优势。

关键词: 电磁场, 大地电磁测深, 视电阻率, 阻抗相位, 地震前兆, 静海地震台