반복적인 텐서 벗기기를 이용한 자기지전류 탐사 자료에서의 해양효과 제거

Abstract

When magnetotelluric (MT) data are obtained in vicinity of the coast, the sea can distort observed MT responses of subsurface, especially those of deep part. We introduce an iterative method to correct the sea effect, based on the previous topographic correction method which removes the distortions due to topographic changes in seafloor MT data. The method first corrects the sea effect in observed MT impedance, and then inverts corrected responses in a model space without the sea. Due to mutual coupling between sea and subsurface structure, the correction and inversion steps are iterated until changes in each result become negligible. The method is tested for 1-D and 2-D structure using synthetic MT data produced by 3-D forward modeling including surrounding seas. In all case, the method closely recovers the true structure assumed in generating synthetic responses after a few iterations. To test the applicability of the proposed method to field data, we apply the method to real MT data acquired from the Jeju Island, Korea. The distortions due to the surrounding sea start to appear below about 1Hz, and this result strongly suggests that the sea effect should be corrected in order to obtain more accurate and reliable interpretation on the subsurface.