INVESTIGATIONS OF THE DEEP ELECTRICAL CONDUCTIVITY BENEATH NORTHERN CHINA USING THE SPATIAL GRADIENT METHOD

The spatial gradient method was used in estimating the buried depth of high conductivity layer beneath the region of northern China. Quiet daily magnetic variations recorded at six observatories, Dalian, Changli, Beijing, Hongshan, Taian and Xian, were analysed in this study. The second-order polynomial surface method was used for the calculation of value C. In order to interpret the results, Creal-T curve and |Cimag|-T curve, a four layer structure must be constructed at the least. The conductivity of the bottom layer is extremely high and its buried depth is about 690 km. A sandwiched high conductivity layer probably exists beneath this region, its conductivity 0.325 S/m, its thickness 24.5 km and its top at the depth of 334 km. It must be stressed that the results obtained here is preliminary, its reliability should be investigated and verified in further studies. The electrical structure revealed here is distinctly different from that of south-east China1, therefore the whole feature of the change of the depth should also be investigated in the future.