Lithosphere conductivity structure using the CAM-1 (Lisbon-Madeira) submarine cable

Abstract

SUMMARY Voltage measurements made in the CAM-1 submarine cable located between Sesimbra (Lisbon) and Madeira Island have been used in combination with magnetic observations carried out in the geomagnetic observatory of Guimar (Canary Islands), to estimate the deep geoelectrical structure beneath the ocean. Apparent resistivities and phases were calculated from those data sets. Published geomagnetic deep sounding results were used to correct the CAM-1 response for static-shift distortion. Magnetic transfer function (tipper) and invariant apparent resistivity and phase obtained from the determinant of the impedance tensor (Z det) on-shore in SW Iberia were used in the modelling in order to better constrain some model parameters. The results obtained by 1-D Occam’s inversion and 2-D trial-and-error modelling reveals a resistive zone (300‐1200 � m) between 10 and 200 km depth followed by a decreasing in resistivity with depth. The order of the integral resistivity of the lithosphere beneath the ocean was found lying in the 9 × 10 7 ‐6 × 10 8 � m 2 range. The estimated depth‐conductivity profile was compared with those obtained from studies in the Pacific Ocean, indicating that the Atlantic lithosphere between Lisbon and Madeira is more resistive than that in the Pacific. The most probable explanation for such observation is the long-term stability (or very low activity) of the sampled Atlantic region. A comparison of the depth‐conductivity profile with published theoretical results based on olivine properties shows that our result is compatible with an isotropic and undersaturated mantle.