Publication Date:
2020-10-04
Description:
Two-dimensional (2D) marine magnetotelluric (MT) observations are useful for offshore geological studies, such as natural resource exploration, fault mapping, fluid estimation at subduction zones, and the delineation of the lithosphere-asthenosphere boundary beneath the seafloor. Earth structures are often assumed to be 2D, which allows MT data to be decomposed into a transverse electric (TE) mode and a transverse magnetic (TM) mode. The 2D assumption can effectively reduce both acquisition and computational costs. However, offline three-dimensional (3D) effects and other problems, such as lack/failure of the compass on instruments, are often encountered, making it difficult to decompose data into the TE- and TM-modes. In these cases, 2D inversion may be misleading or may not provide an acceptable misfit to the marine MT observations. Thus, we introduce 2D determinant inversion to the marine MT method to mitigate these difficulties, implemented in the MARE2DEM code, and demonstrate its utility using synthetic examples and a field example. In synthetic examples, the determinant inversion demonstrates an ability to overcome 3D effects caused by 3D anomalies and bathymetry. With confidence from the synthetic tests, we interpret real data acquired in the Gulf of California, Mexico, where not only is the bathymetry 3D in nature, but the external compasses failed to record orientation. The field data can not only be fit to a reasonable misfit with a determinant inversion, but also the resolved conductive zones have a good correlation with known faults. A comparison between the resistivity model from the field data and a seismic reflection section shows that a previously interpreted fault, the Wagner Fault, should be shifted 5 km towards the southwest and made slightly steeper. Thus, the implementation of the determinant inversion may provide a new approach to utilize problematic 2D data.
Print ISSN:
0016-8033
Electronic ISSN:
1942-2156
Topics:
Geosciences
,
Physics
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