Magnetic

The Vema FZ is located close to the magnetic equator, causing the magnetic anomalies to be very weak relative to ambient noise. Corrections for diurnal variations are important in this area because they reach the same order of magnitude as the sea-bottom anomalies. We deployed one magnetometer based on the Overhauser effect, at a distance of 230 m from the GPS antenna. All magnetic profiles are located south of the Vema transform in the S.American plate. The data sampling was performed at rate of 6 sec by the navigation system.

The initial processing of magnetic data showed that the the use of a single transducer configuration did not hamper the usefulness of the data. Fig. 5 shows part of magnetic profile VEMA-15 S, low-cut filtered (wavelength $\ge$ 6 hours, as an attempt to correct diurnal variations), after IGRF-95 removal, compared with its synthetic profile obtained by forward modeling based on CANDE1995 time scale, assuming 1 km magnetized layer. We note a general agreement between the two curves for a spreading rate at 15.5 mm/y, averaged over the last 5 Ma.

Figure: .