POSSIBLE CHANGES OF EARTH CONDUCTIVITY ACCOMPANYING THE TANGSHAN EARTHQUAKE OF 1976

Time changes in transfer functions of short period geomagnetic variations are studied in order to investigate the possible anomaly of earth conductivity in relation to the Tangshan earthquake of 1976. The results indicate that there are appreciable negative anomalies in the transfer functions A at two observatories located respectivily 5 km and 60 km from the aftershock area. But the anomalous change of A is not obvious at another observatory, 145 km to the west of the aftershock area. If anomalous change of earth conductivity exists, then the depth of greatest change is that corresponding with the period of 14—20 min., and the inclination of the boundary of the conductor under ground may have decreased about 2.7°at Changli.