Real Data

The sections below show published real data applications of MARE2DEM for inverting magnetotelluric and controlled source electromagnetic data. All figures shown here were made using MARE2DEM’s MATLAB plotting tools, which support various functions such as interpolated shading, resistivity contours, sensitivity contours, sensitivity masking, well-log overlays, seismic overlays, a wide array of color maps, and many other customizable appearance options.

Note that the seawater and air layers (which are fixed parameters) have been turned off in the plots for marine models below. Also, only the central region of interest is shown for each model; the entire model domains extend 100’s or 1000’s of km beyond the central region of interest shown in the figures, where these outer padding regions ensure that model boundary reflections do not corrupt the finite element solutions in the region of interest.

East Pacific Rise Mid-Ocean Ridge MT


Fig. 10 Example of using an unstructured grid of triangular free parameters to invert seafloor MT data from the East Pacific Rise spreading ridge at 9º 30’ N, revealing a conductive region of upper mantle upwelling and partial melting. Small triangular parameters are used at the seafloor to allow for near-surface variations and to accomodate rugged bathymetry, while deeper in the mantle larger triangles are used. Inverted white triangles along the seafloor show the MT receiver locations. Modified from: Key, K., Constable, S., Liu, L., & Pommier, A. (2013), Electrical image of passive mantle upwelling beneath the northern East Pacific Rise. Nature, 495(7442), 499–502, DOI: 10.1038/nature11932.


Fig. 11 Behind the scenes, MARE2DEM generates finite element (FE) meshes for the forward calculations of the EM fields. These unstructured triangular finite element meshes are automatically generated and adaptively refined using a goal-oriented a posteriori error estimator for the FE solution. This image shows an example FE mesh (thin black lines) near the seafloor for the model above. Notice how the FE mesh conform to the free and fixed parameter polygons (thick lines). The FE mesh shows the most refinement near the MT stations, where fine meshing ensures accurate electromagnetic fields are computed.

Middle American Trench Offshore Nicaragua MT and CSEM


Fig. 12 Example of using an unstructured grid of quadrilateral parameters to invert seafloor MT data from the Middle America Trench offshore Nicaragua for triaxially anisotropic conductivity, revealing an anisotropic conductive asthenosphere layer consistent with partially molten mantle. Upper panel shows the y component of resistivity and the lower panel shows the y/x resistivity anisotropy ratio. Modified from: Naif, S., Key, K., Constable, S., & Evans, R. L. (2013), Melt-rich channel observed at the lithosphere-asthenosphere boundary. Nature, 495(7441), 356–359, DOI: 10.1038/nature11939.


Fig. 13 Inversion of marine CSEM data crossing the Middle America Trench. Shaded colors and contours show resistivity while the gray masked region in the seafloor masks areas the data are insensitivity to, as determined by the normalized Jacobian matrix (see Normalized Sensitivity) . Modified from [Key16] and Naif, S., Key, K., Constable, S., & Evans, R. L. (2016), Porosity and fluid budget of a water‐rich megathrust revealed with electromagnetic data at the Middle America Trench. Geochemistry Geophysics Geosystems, 17(11), 4495–4516, DOI: 10.1002/2016GC006556.


Fig. 14 A similar plot to the one above, but now with shaded colors showing the log10 sensitivity (see Normalized Sensitivity) and contours showing log10 resistivity.


Fig. 15 Example screen shot of CSEM response plot made with the interactive MATLAB code plotMARE2DEM_CSEM.m. Upper row: symbols show the amplitude and phase response at three frequencies for a single receiver along with the corresponding model response (black lines). Lower row: normalized residuals for the data fit.


Fig. 16 Example screen shot of CSEM misfit breakdown plot made with the interactive MATLAB code plotMARE2DEM_CSEM.m. The misfit breakdown plot is useful for showing how well the data is fit as a function of receiver position, transmitter position, frequency, data type and transmitter-receiver range. Regions with large misfits can indicate where they data may be noisy or have problems, or where the model mesh needs to be refined to allow for smaller scale features required to fit the data.

Gemini Salt Body, Gulf of Mexico


Fig. 17 Inversion of marine MT data from Line I at Gemini Prospect, Gulf of Mexico. This inversion relaxed the roughness penalty along the seismically imaged top of the Gemini salt body (white line), allowing for a sharp jump in inverted resistivity. Penalty cuts like this are easily created in MARE2DEM’s graphical user interface Mamba2D.m. Modified from Key, K. W., Constable, S. C., & Weiss, C. J. (2006), Mapping 3D salt using the 2D marine magnetotelluric method: Case study from Gemini Prospect, Gulf of Mexico. Geophysics, 71(1), B17–B27. DOI: 10.1190/1.2168007.