Coast effect in geomagnetic field variations in Kamchatka

• download

Coast effect has been studied using numeric 3-D modeling of magnetotelluric (MT) field. It is associated
with a sharp contrast of conductivity of the surface and water upper layers in the basin of the Sea of Okhotsk
and the Pacific Ocean. The contrast yields up to 3-4 orders. This leads to high concentration of electric cur-
rents in the Sea of Okhotsk and the Pacific Ocean. Combined inductive effect of these currents in Kamchatka
generates complex behavior of geomagnetic-variation parameters. Frequency tipper curves reveal 4 zones with
different degree of coast effect. On the western coast the maximum values of coast effect are observed in periods
of 400-500 s. When moving to the east, the coast effect from the Sea of Okhotsk decreases while that of the
Pacific Ocean increases and becomes stronger on the eastern coast. Maximum of coast effect is observed in
periods of about half an hour. It exceeds almost 4 times the coast effect on the western coast. Maximum of
coast effect on the eastern coast is associated with the saturation of the deep trench with electric current that
induce vertical magnetic field component crossing Eastern Kamchatka. Boundaries of the area on which coast
effect is observed from the Sea of Okhotsk or the Pacific Ocean depend on the periods of geomagnetic field
variations. At time intervals T>500 s the whole territory of Kamchatka is embraced by coast effect from the
Sea of Okhotsk or the Pacific Ocean. Areas free from coast effect are observed only at period of 100 s in a
bigger middle part of the peninsular and at period of 1600 s a narrow zone of 50 km wide. The 3-D effects of
geomagnetic field variations are observed at various scales and at different frequencies. At short intervals up to
400 s the effects are related to the current flowing of complex coastline contours. With increasing variations in
time intervals the effects attenuate and go down at T= 10000 s. In the meantime new effects are emerged related
to the Kamchatka current flow defined as a 3-D elongated geoelectric heterogeneity in well conductive sea water.