Abstract: MT data were acquired at two sites after Zhangbei Shangyi M6.2 earthquake on January 10,1998.At 511 site ,which is 26km in distance to southeast from the epicenter,the data were obtained in January 13 and 21 of 1998,where the MT measurement was done in June 1 of 1994.At site MMC MT measurement was made continuously from January 16 to 20 of 1998.The results indicate that : (1) Resistivity for TE polarization decreased within period range 0.24 sec.and resistivities for M polarization increased generally in comparison with data of June 1,1994.(2) The resistivity for both polarizations at site MMC increased gradually from day to day.The minimum appeared on January 16 and the maximum appeared on January 20.(3) The change of resistivity possibly reflected the resistivity resumption process after main shock.In addition,electric structure of subsurface corresponding to the MT data are analysed.Activity of the fluid in the crust is possibly related to the change of resistivity.

Key words: Magnetatelluric sounding, Apparent resistivity, ZhangbeiShangyi earthquake

摘要： 在张北-尚义地震区震前已有大地电磁资料测点(511点)进行了两次重复观测,在震中区测点(MMC点)进行了连续4昼夜的观测。测量结果显示:(1)与震前资料相比,511测点沿电性构造走向方向(NNW)在0.2～4s周期范围内的视电阻率减小,垂直走向方向的视电阻率增大;(2)MMC测点两个方向在0.2～10s周期范围内的视电阻率随测量时间逐渐增大; (3)511测点两次重复观测和MMC的观测可能都反映出震后电阻率正在逐渐恢复。此外,还对地震前后地下结构的变化进行了分析。初步推测,观测到的电阻率变化是由于地下流体活动引起的。

关键词: 大地电磁测深, 视电阻率, 张北-尚义地震