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

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