Local anomaly of earth-current and earth-resistivity
Yanagihara, K. & Yokouchi, T.
The electric field measured on the earth surface changes rather suddenly from a place to another in geologically complicated regions such as Japan. Cagniard's magneto-telluric analysis does not always apply in that area. Stream lines of earth-currents are decided firstly by the distribution of sea water, sediment and crustal rock and secondly by the small scale anomaly of resistivity. In the region of high resistivity rocks, which are surrounded by uniform sediments, the electric field increases strongly. The resistivity of the deeper layer calculated from those data by Cagniard's apparent resistivity, ρa=0.2 T(E/H)2 is higher by the square of the increasing factor of the electric field than the real one. Two dimensional approach gives 7 for the factor of increase at Kakioka. The measured vertical distribution of resistivity at Kakioka(Yanagihara, 1965) coincides well with the result of magneto-telluric analysis when the locality of earth-currents is taken into consideration.