Current channelling, the consequences for electromagnetic soundings

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Abstract
The presumed occurrence in the crust of the Earth of concentrated currents which are not caused by local induction is at present a controversial subject. Trying to assess the effects such so‐called "injected channel currents" may have on magnetotelluric (MT) and geomagnetic deep soundings (GDS), we have looked at the way currents of purely internal origin would manifest themselves in records of electromagnetic soundings. If all the electromagnetic fields are the result of true local induction these fields will combine above the structure into a nearly perfect standing wave. If, however, anomalous currents are injected from outside, the fields will comprise an additional travelling wave which gives away the injected currents. Therefore, the conclusion from quasi‐static theory that it is impossible, over a one‐dimensional structure, to separate internal and external fields cannot be upheld and MT and GDS soundings will be affected by these anomalous injected currents.

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