| Popis: |
A modeling study has been undertaken to investigate the resolution and accuracy of marine magnetotelluric (MT) and controlled source electromagnetic (CSEM) data to image the base of basalt and sediments in an environment representative of the North Atlantic Margin. The three dimensional (3D) model was constructed using regional well logs, seismic and geologic data to create a cube of porosity and saturation that is 32 km long, 16 km wide and 5 km deep. The porosity and water saturations were then converted to resistivity using well log-derived relationships in the sediments above the basalt, three different volcanic units, sub-volcanic sediments, and flat lying basement. Transverse anisotropy was incorporated in most of the units by making the vertical resistivity more resistive than the horizontal, while the flow basalts were made tridiagonally anisotropic to account for lower resistivities along strike caused by faulting, and higher vertical resistivities caused by the flow structures. Simulated MT and CSEM data were computed using a 3D finite difference algorithm. A twodimensional (2D) pixilated inversion algorithm was used to produce images of the synthetic MT and CSEM data along lines that were roughly perpendicular to the regional strike of the basalt structure. The images show that the MT data by themselves lack resolution to warrant use alone, but help to constrain the inversion process when jointly inverted with CSEM data. Constraints in the form of a discontinuity at the top of the basalt further enhance image resolution. |
