An analogue model study of EM induction in the Japan-Korea-China region

Abstract

Electromagnetic induction in the coastal region of Japan-Korea-China is studied using a scaled laboratory analogue model. The model includes a simulation of the known ocean bathymetry, the complex coastlines and the deep conductive Pacific trench. Model measurements of the electromagnetic field components are carried out for simulated periods of 15–180 min for two mutually perpendicular polarizations of a uniform horizontal inducing source field. In-phase and quadrature B x , B y , and B z model measurements are examined in detail for a series of traverses over Japan, the Korean peninsula, and the coastal region of China and the U.S.S.R. Large anomalous in-phase model magnetic fields are observed over the Korea-Japan strait for E-polarization and over the Bohai, Tsugaru, and La Perouse straits for B-polarization owing to current channelling. The significant responses observed at short periods over the peninsulas in the shallow coastal areas decrease with increasing period. Large gradients in the in-phase B 2 field are observed over Japan for E-polarization for both short and long periods owing to the effects of induced currents in the surrounding oceans. Thus induction arrow responses over all regions of Japan are expected to show the dominant effects of the ocean. A comparison of analogue model and field site induction arrows over the Kii peninsula of Japan indicates that, the ocean effects alone cannot fully account for the observed responses. The differences in the model and field results can be attributed to lateral inhomogeneities in the conductivity structure under Japan.