Authors:	Baumann, Tobias Samuel
Title:	Geodynamic inversion to constrain the rheology of the lithosphere
Online publication date:	26-Apr-2016
Year of first publication:	2016
Language:	english
Abstract:	The aim of this thesis is to link both, an inversion approach and physically consistent numerical models of lithospheric deformation to infer rheological properties of the lithosphere directly from geophysical observations at the Earth’s surface. Experimental results can be incorporated as prior knowledge with large uncertainties such that the method of geodynamic inversion is complementary to rock deformation experiments and describes an independent approach to verify geodynamic and geological concepts. The thesis is a cumulative work with four chapters composed as mostly independent papers that have already been published in peer reviewed journals, submitted or prepared for submission. Chapter 2 covers the first attempts of constraining effective viscosities and densities through joint inversion of gravity and surface velocity data. The study is divided into two parts, a theoretical part, where the benefits of a joint inversion of gravity and velocity are analytically demonstrated, and a synthetic case study to demonstrate the feasibility of Bayesian-type inversions in the context of numerical geodynamics. In chapter 3, the methodology is applied to the full scale of the lithosphere. A synthetic study is conducted to test the methodology for the use with non-linear rheologies, which naturally involves a lot more of unknowns. Tests with a known and a parameterised temperature structure reveal the effect of temperature on the inversion results and show that the effective non-linear viscosity structure can be estimated within the uncertainty limits. Beside the synthetic study, the major part of the chapter deals with a 2D profile through the India-Asia collision system. The results are not unique and multiple end-member models coexist. However, there are stable features that most of the acceptable models have in common, for example a strong, i.e. high-viscosity, lithospheric mantle of India. Chapter 4 deals with the appraisal of non-unique geodynamic inversion results, which is conducted with a two-level approach that involves a well-established unsupervised machine learning technique and additional clustering. The analysis enables a successful classification of all models into four end-member categories, which are mainly confined through the existence of a few key characteristics. The classification also reveals what causes the non-uniqueness of the inversion results in terms of observational constraints. Chapter 5 focusses on the India-Asia collision system as well, but from a 3D perspective. The aim of this study is twofold and involves (i) a compilation of multiple seismological data into a 3D geometry of the present-day India-Asia collision, and (ii) an inversion approach to constrain a best-fit effective viscosity structure by minimising the misfit to the observed horizontal GPS velocity field. The analysis demonstrates that an interplay of strike-slip faults, a low-viscous lower crust and lateral heterogeneities, i.e. cratonic blocks, such as the Sichuan basin, is crucial to reproduce the characteristic flow field that is observed in the Eastern Himalayian syntaxis.
DDC:	550 Geowissenschaften 550 Earth sciences
Institution:	Johannes Gutenberg-Universität Mainz
Department:	FB 09 Chemie, Pharmazie u. Geowissensch.
Place:	Mainz
ROR:	https://ror.org/023b0x485
DOI:	http://doi.org/10.25358/openscience-2489
URN:	urn:nbn:de:hebis:77-diss-1000004140
Version:	Original work
Publication type:	Dissertation
License:	In Copyright
Information on rights of use:	https://rightsstatements.org/vocab/InC/1.0/
Extent:	179 S.
Appears in collections:	JGU-Publikationen