General

The EMIX MT package is offered to interpret MT, AMT and CSAMT data. EMIX MT performs forward and inverse modeling of layered earth models. Solutions are in terms of either apparent resistivity or apparent resistivity and impedance phase data.

EMIX MT uses the input impedance concept of J.R. Wait (Theory of Magnetotelluric Fields, National Bureau of Standards, 1962) for forward modeling of the impedance at the surface of the earth or on the bottom of a lake or sea. Sounding curves are then converted into apparent resistivity and phase of the impedance in degrees. EMIX MT uses the Inman-style ridge regression approach of non-linear least squares curve fitting for inversion calculations.

EMIX MT is an interactive, graphically oriented, forward and inverse modeling program for interpreting Magnetotelluric (MT), audio Magnetotelluric (AMT), and controlled source audio Magnetotelluric (CSAMT) sounding data in terms of a layered earth (1-D) model.  Sounding curves can be entered as a function of period or frequency, and apparent resistivity amplitude data can be interpreted with or without impedance phase data.

Data can be shifted (scaled by a constant) either by using mathematical operation in the Magnetotelluric Data and Error Bars spreadsheet, or by using the Shift curve option while in interactive graphics mode of the INTERPRET command.

Inverse modeling enables you to obtain a model that best fits the data in a least squares sense. This is done using ridge regression (Inman, 1997) to interactively adjust the parameters of a starting model supplied by the user. Starting models for inversion can have up to 8 layers.  You can constrain some of the starting model parameters so the inversion will not adjust them. Constants can be applied by fixing (or freezing) a parameter, or by imposing limits on a parameter.  Parameters can be resistivity + thickness of layers, or resistivity + depth to bottom  of layers.  If phase data are present, each layer has an additional parameter.

Smooth modeling enable you to automatically interpret MT amplitude and impedance phase sounding data in terms of a smooth model with up to 19 layers. The model depths are logarithmically spaced and are generated from a minimum and maximum depth.  The minimum and maximum depth can be user-specified or can be automatically generated.  Model resistivity are normally initialized to the best fit homogeneous half-space resistivity. Inversion can be carried out in either interactive or batch mode, using ridge regression or William of Occan's smooth model concept.

Equivalence analysis enables you to generate a set of equivalent layered models, which are alternative models that fit the data nearly as well as the best-fit model, but differ from it. Equivalence analysis also indicates the allowable range of each of the model parameters.

New- Emix MT allows for the specification of a profile distance, land-based or lake/sea bottom and TE, TM or No specified mode. For lake bottom data, magnetic sensor position is specified in addition to profile distance. This allows Emix MT2D to access the Emix MT database and assign a TE and a TM mode sounding to a station at the specified location along the profile.

Emix MT can also handle controlled source data taken with a grounded wire. The grounded wire is assumed to be a dipole and the receiver is assumed to be oriented so that the electric field receiver is parallel to the source wire.

Standard Components

Emix MT v2 software and manual.