A Geomagnetic Variation Anomaly in the Northern Pyrenees

Summary Sixty stations measuring the time variations of the Earth's magnetic field were operated from 1972 to 1974 in the Northern Pyrenees. Magnetograms show a very large anomaly in the vertical and horizontal variation fields for the period range from a few minutes to a few hours. Owing to the particular measurement and reduction techniques used it was possible to show that, for the above period range, the anomalous field is the product of a function of space by a function of time. This anomaly corresponds to a current concentration the geometry of which is invariant with time. Most of the currents associated with the anomaly flow at a depth smaller than 15km. The orientation of the conductive structure is different from the orientation of superficial structures; this structure could correspond to old sedimentary basins inside the palaeozoic basement or (and) to a hidden accident in the basement as suggested by seismic evidence.