Laboratory model magnetic fields for the Hainan Island region.

Abstract

The behaviour of the electromagnetic fields over the Hainan Island region of the South China Sea is studied using a scaled laboratory analogue model. The model source frequencies used simulate periods of 5 min. to 30 min. in the geophysical scale. To examine the electromagnetic field variations due to the irregular coastlines, the deep ocean, a narrow ocean channel, and an atoll (modelled as a seamount), field components for individual traverses over the model are presented.The coast effect for the bay coastline is visible only for short periods at which the depth of the bay is at least .1 skin depths. The response of the seamount, overlain by a 500m depth ocean, differs greatly from the response of an island. Electric current flow over the seamount, confined to this thin layer, produces a quadrature field directly opposite to that for an island. Buried features such as the seamount and depth profile of the deep ocean show the largest in-phase response at the lower frequency where the overlying ocean is much less than .1 skin depth thick.