Franz, Gesa, Moorkamp, Max, Jegen, Marion , Berndt, Christian and Rabbel, Wolfgang (2021) Comparison of Earth models of the Namibian continental margin derived from Joint MT and Gravity Inversions. [Poster] In: 81. Jahrestagung der Deutschen Geophysikalischen Gesellschaft (DGG). , 01.03.-05.03.2021, Kiel (online) .

Abstract

Combined analysis of multiple geophysical methods is a key practice to reduce model uncertainties and improve geological interpretations. Various approaches to combine several data sets or physical models in joint inversion have different advantages and challenges. We present a comparison of two ways to integrate marine magnetotelluric (MT) with gravity data along the Namibian passive continental margin and also compare them to a single-method MT inversion. This study area offers an excellent setting, because multiple tectonic processes (e.g. rifting, magmatism, post-breakup sedimentation) lead to various lithological units with distinct physical properties (e.g. continental-, transitional-, and oceanic crust, fault systems or sedimentary depocenters). The two joint inversions are a cross-gradient coupled 3D inversion of marine magnetotelluric data with a fixed structural density model based on gravity modeling, and a joint inversion of the same MT data with satellite gravity data. Structural coupling with the blocky density model enforces harsh resistivity changes in an otherwise smooth model and helps reducing excessively smeared inversion artifacts. Although the edge-like features complicate direct model interpretation, they indicate alternative ways to fit the MT data, while simultaneously matching seismic observations integrated in the density cross-model. For the second approach, the large solution space of the satellite gravity data inversion limits the improvements through joint inversion compared to a single method MT inversion. The resulting joint inversion resistivity model differs only marginally from the single-method resistivity model, while the joint density model inherits some of the rather questionable resistivity model features. Our study demonstrates how joint inversion of multiple data aids model interpretation. The resulting resistivity models provide equally well-fitting alternatives to single-method evaluation, and additionally fit other geophysical method’s observations (i.e. gravity and seismic methods). The direct comparison of the impact of constraining MT inversion with either a fixed structural model or a coupled data inversion highlights how well the MT solution space may be confined. In our study, the fixed structural model constraint outperforms the joint MT-gravity data analysis.

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