Anomalous transient variations of the geomagnetic field in northern Morocco and southern Spain have been described previously for periods ranging from 10 min to 2 h. These results have been reinvestigated with regard to their tectonic implications.The main result obtained is evidence for a conductive structure that electrically connects the Atlantic Ocean to the Mediterranean Sea. This conductive structure coincides with a zone of fractures, extending over several hundreds of kilometres and deeply penetrating the crust, that may form the southeastern boundary of the Alboran block.We also show that the deviation and channeling of electric currents by lateral contrasts of conductivity may account for most of the features of the observed anomalous field in southern Spain and northern Morocco.

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