On the Subterranean Electric Structure near Kanoya
Oshima, H.
Abstract
Behavior of anisotropy of earth-currents and the Cagniard's magneto-telluric analysis are studied as a preliminary research on the vertical distribution of earth-resistivities in the vicinity of the Kanoya Magnetic Observatory. This study is the first step to the research of subterranean electric structure near Kanoya. Data of geomagnetic and earth-current rapid-variations at Kanoya are used in this study. It is found out that the main axis of anisotropy changes its direction clockwisely with increase of the period of geomagnetic rapid variations from several 10 sec to several 10 min and simultaneously anisotropy is intensified. At Kanoya, it may be reasonable to apply the Cagniard's simple magnetotellurics to the east-west component of the earth-current, because the component is depending mainly on horizontal intensity of geomagnetic field variation, as shown in Fig. 3. And three layered model, ρ１=6Ω.m, ρ２=40Ω・m, ρ３≧2×10・ 4Ω・m, h１=2 km, h２=30 km, is deduced from the result of it's application.
In the last section, some speculations are described on interpretation of this model, but further discussions will be done after more sufficient research.
