Magnetotelluric Data Analysis using Swift Skew, Bahr Skew, Polar Diagram, and Phase Tensor: a Case Study in Yellowstone, US
Magnetotelluric Data Analysis using Swift Skew, Bahr Skew, Polar Diagram, and Phase Tensor
Keywords:
Bahr skew, dimensionality, magnetotellurics, phase tensor, polar diagram, swift skewAbstract
Magnetotelluric (MT) method is a passive electromagnetic (EM) technique for measuring fluctuations of the nature electric (E) and magnetic (B) fields at the Earth surface, which correspond to apparent resistivity. Prior to MT data modeling, to convert apparent resistivity to true resistivity, analyzing the dimensionality of MT data is needed. In this study, the MT data were taken from US Array in Cascadia Subduction Zone, particularly around the Yellowstone National Park, US. The MT data analysis used four parameters, i.e., Swift skew, Bahr skew, polar diagram, and phase tensor. Additionally, 1D modeling for XY and YX components was performed. Thus, correlations between the model and the dimensionality data in the study areas were revealed. Data analysis from Swift skew parameter indicated the 3D character of MT data (i.e., Swift skew value more than 0.3). The majority of the polar diagrams were peanut shaped, and a lot of phase tensors had an ellipse shape with large β value, indicating 3D character. Although 3D inversion modeling for these data was more proper (because the data exhibited 3D character) than 1D inversion, the 3D inversion algorithm was computationally expensive. Thus, in this study, we performed 1D inversion MT modeling which revealed that in some cases, 1D and 3D inversion results exhibited similarities.
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