A sea-to-groumd magnetovariational method

摘要

The magnetovariational (MV) approach consists of recording the natural time-varying magnetic field at two different levels below the ground surface The MV method can also b used in marine researches using waterproof senosr devices. However, a weak point of marine measurements is the lack of stability of any sensor hanging in seawater. To overcome this difficulty, in this paper we propose an alternative aray design consisting of a magnetic sensor device firmly laid down on the sea floor and a second device located on land at a remoote station where the subsoil conforms to a 1-D structure. This circumenance and the uniformity of the primary magnetic field over largely extended regions allow the electromagnetic compoents in seavwater to be readily estimated using the measured magnetic field at the remote station. By these estimates, the two-level MV response across the sea water layer can be definitively simulated. The same procedure can be adopted to simulate the magnetotelluric sounding at any level in seawater. Finally, the installation of a second remote station inland is sgugested in order to minimize the effect of nosie on the estimates of the apparent impedivity functions. Reliability and usefulness of the new sea-to-ground MV method are tested on two snthetic examples.