Universität zu Köln

Nienhaus, Hannah ORCID: 0009-0000-5684-9626 (2025). Three-Dimensional Inversion of Multi-Component Loop-Source Transient Electromagnetic Data: Investigating the Roter Kamm Impact Crater, Namibia. PhD thesis, Universität zu Köln.

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Abstract

The Roter Kamm impact crater is located in the southern Namib Desert. This location has been restricted from public access for over a century, significantly limiting research activities. This thesis determines the multi-dimensional shape of the sediment cover of the impact structure by applying 1D and 3D inversion schemes to loop-source transient electromagnetic data, while simultaneously comparing the single-loop and multi-component fixed-loop set-ups in terms of model resolution. The Roter Kamm impact crater, which belongs to one of multiple survey areas of the Collaborative Research Center CRC 1211 "Earth Evolution at the Dry Limit", is of particular interest in this study. The CRC 1211 investigates the evolution of the areas in hyper-arid deserts by applying various methods from disciplines such as geosciences, physics and biology. In the framework of this thesis the fixed- and single-loop TEM set-ups were employed. The two methods can be used complementary to achieve a maximum resolution in shallow and large depths depending on their transmitter size. The single-loop configuration employs loop sizes smaller than those used for the fixed-loop configuration. The fixed-loop configuration uses one stationary large transmitter and several multi-component receivers, both inside and outside the transmitter. This configuration, especially the horizontal component, is sensitive to lateral conductivity boundaries. A variety of synthetic 3D TEM studies present the effects of a multi-dimensional subsurface and topography on transient data, and additionally highlight the superior performance of fixed-loop data-sets in multi-dimensional inversion schemes. Comprehensive 3D inversion results, corroborated by a 2D AMT resistivity model, reveal a large, lens-shaped conductor inside the impact structure. This conductor likely represents water-saturated sediments overlying brecciated bedrock. This work marks the first independent geophysical model of the Roter Kamm impact crater.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Nienhaus, Hannah h.nienhaus@uni-koeln.de orcid.org/0009-0000-5684-9626 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-780496
Date:	2025
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Geosciences > Institute for Geophysics and Meteorology
Subjects:	Earth sciences
Uncontrolled Keywords:	Keywords Language Electromagnetic Methods English 3D Modeling and Inversion English TEM English Time Domain English Roter Kamm UNSPECIFIED
Date of oral exam:	10 March 2025
Referee:	Name Academic Title Tezkan, Bülent Prof. Dr. Hördt, Andreas Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/78049