An analogue model study of electromagnetic induction in the Queen Charlotte Islands region.

Abstract

In order to ease the interpretation of geomagnetic data for resource charting and tectonic studies of the Queen Charlotte Islands region, the behaviour of the electromagnetic variations over the region is studied using a laboratory analogue model. The results indicate that conductive channelling is important in Hecate Strait for both E and H source field polarizations. Current deflection is observed at Rose Point for E-Polarization and at the northern and southern tips of the Queen Charlotte Islands for H-Polarization. Model results for simulated variations of 4, 40, and 120min show a wide range of field values over the Queen Charlotte Islands, for example, HZ varies by a factor of 4 or more between coastal and inland locations for E-Polarization at short periods and by as much as a factor of 5 between certain coastal locations at long periods. The model results show that in decreasing the depth of the conducting layer in the mantle from 200 to 100km, the Hz, Hx, Ex, and EY anomalies are attenuated by 20%, and the Hy anomalies by roughly 8% over the deep ocean and by 12% over Hecate Strait for 4min period variations.

Laboratory model magnetic fields for the Hainan Island region.

“…On the basis of ocean sediment information given by LuD-WIC et al (1979) and NINO and EMERY (1961), it was appropriate to add the equivalent of 150m of seawater to account for the sediments in the coastal region extending roughly to the 1km ocean depth contour. The method of constructing the model ocean and suspending it in the salt water tank was the same as that discussed previously in earlier work (e. g. Dosso et al, 1980aDosso et al, , 1980bCHAN et al, 1981a;HEBERT et al, 1983). The atoll (Zhongsha Islands) is one of the important features in the present model.…”

“…Examples of laboratory analogue model studies for various islands near continental coastlines are provided by NIENABER et al (1979) for the Vancouver Island region, Dosso et al (1980a) for the British Isles region, Dosso et al (1980b) for the eastern coastal region of Canada, CHAN et al (1981a) for the Queen Charlotte Islands region and HEBERT et al (1983) for the Newfoundland region. These studies examined the channelling of telluric currents in the conductive sea channel between the island and continent, the effect of the nearby deep ocean on the induced electric currents and the associated electric and magnetic fields.…”

“…This method has been used successfully in several models (CHAN et al, 1981a;HEBERT et al, 1983). A fairly uniform horizontal inducing field (RAMASWAMY et al, 1975;NIENABER et al, 1976) was provided by an overhead, oscillating double line current for what is defined as the E-polarization of the source field.…”

“…The laboratory analogue model, the measuring equipment, the source field and end effects have all been described previously (Dosso, 1966(Dosso, , 1973CHAN et al, 1981a) of 15kHz and 90kHz simulate geomagnetic variations with periods of 30 min. and 5 min.…”