Sea effect correction in magnetotelluric (MT) data and its application to MT soundings carried out in Jeju Island, Korea

Abstract

When magnetotelluric (MT) data are obtained in the vicinity of the coast, the surrounding sea makes it difficult to interpret subsurface structures, especially at the deep parts of the subsurface. We apply an iterative method to remove the sea effect. The iterative method was originally developed to remove the distortion due to topographic changes from MT data recorded on the seafloor. The iterative sea-effect correction method is carried out in two steps. The first corrects the sea effect, whereas the second inverts the sea-effect-corrected responses. The two steps are alternatively carried out, until the criterion for either the inversion or the sea-effect correction is satisfied. Because the surrounding 3-D sea bathymetry is only incorporated into forward modelling for the sea-effect correction, it can be more robust than the method that directly incorporates 3-D sea bathymetry into a model space for inversion. The synthetic examples show that the sea-effect correction method yields an inverted model comparable to the true model. By applying the sea-effect correction method to real field data acquired in Jeju Island, Korea, we also demonstrate that the sea-effect correction method effectively removes the sea effects from the 1-D and 2-D real field data, which helps enhance the inversion results. On the basis of these results, it may be concluded that the iterative sea-effect correction method can be used as a promising technique for recovering the true response of the subsurface in MT data suffering from sea effects.