Local Geodynamic Model And Layer Structure For Enhancing Understanding Of The Earth And Lunar Dynamics

Geophysical data can be used as key data to discover and understand the dynamic process or characteristics of the Moon and the outer layer of the Earth.Despite well-established approaches to understand the Earth and the Moon,geophysical constrains in some areas are missing.For instance,difficulties in installation of seismometers in some areas due to inaccessibility and the financial constraints,renders the Earth to not fully be covered with seismic stations.Lack of seismic constraints data did not spare the Moon,with available data acquired in the 1960‘s by the Apollo mission within a very small area.Despite the increase in the volume of dense seismological networks in some parts of the world,some areas in Africa,Mainland China and Antarctica still suffers from lack of dense coverage of seismological network.The advent of satellite derived potential field data from GRACE,GOCE and/or GRAIL missions have produced a global geophysical data coverage.However,seismic data are still used as constraints and prior information in subsurface modeling due to the non-uniqueness of the potential field data.Besides geophysical data(GOCE-gravity models and seismological data),geological information is also exploited to cover the gaps in creation of optimal gravity-derived models using existing geophysical methods.The regularizing inversion,which is based on the Gauss-Newton formulation of Bott‘s equation,was used to derive the Moho topography for Botswana,Mainland China and Antarctica,in spherical approximation using tesseroids,which were validated using seismic data.Gravity data were first corrected for the Bouguer effect,terrain effect,and gravity effect due to sediments.In Antarctica,the gravity effect due to vertical deformation of the lithosphere caused by ice load was introduced and included to resolve the Moho on a fully-relaxed lithosphere.3D density models for the Rümker region(Proposed landing site for Chang‘E-5 mission)in the Northern Oceanus Procellarum and for the Von Kármán Crater(Landing site for the Chang‘E-4 mission)in the South-Pole Aitken and Eastern Botswana were resolved using a depth weighting algorithm in spherical coordinates.Due to lack of seismic data,the gravity inversion was constrained using known geological/geophysical parameters,a regularizing parameter obtained from the L?curve method,and restrictive condition implemented using Lagrangian multiplier approach.In the first part of this thesis,in Chapter three(3),the geodynamics of Mainland China and Antarctica is explained based on the improved crustal thickness models.The crustal thickness model for Antarctica shows a thicker average crust in East Antarctica and a thinner one in West Antarctica.The thickest crust is in the Gamburtsev Sub-glacial Mountains with a Moho depth of over 40 km.Comparisons with existing models show a good correlation in gravity-constrained areas.Differences appear in the sedimentary basins and crust with thickness closer to seismic point observations.The crustal thickness model for Mainland China exhibits a minimum value of?26 km in Eastern China to a thick crust of over 75 km under the Tibetan Plateau.The model also exposed two East-West fold belt trends on the Tibetan Plateau that was not visible in previous models,which indicates the effect of collision of Indian and Eurasian Plates.Western and Eastern China is separated by a 44 km thick crust,and a 37 km NNE trend line separates the stable eastern cratonic blocks from the thinned crustal blocks.Both models in mainland China and Antarctica yields an improved representation of crustal features over previously crustal thickness models,in comparison with tectonic and geologic information.In the second part of this thesis,in Chapter four(4),the crustal thickness and density structure models beneath Botswana were integrated with previously obtained geophysical and geological information,which enables the understanding of the recent geodynamic processes.The occurrence of a M_w 6.5 Earthquake on 3^rd April 2017,in an area with no historical record of large magnitude Earthquakes or active faults and?350 km away from the seismically active Okavango Rift Zone,bring into perspective a need for further understand the geodynamics of Botswana.The crustal thickness model exhibit a thinner crust(35-41 km)that underlies the Okavango Rift Zone and sedimentary basins.Cratonic regions and orogenic belts show a thicker crust(40-46 km).The boundary of the Congo craton in Botswana,which was illusive,is clearly defined from the model.The model also shows localized zone of thinned crust(?40 km)along the edge of the Kaapvaal Craton,surrounded by thick crust(42-46 km).Lower crustal erosion that resulted in a thin crust is also proposed as the result of thermal fluid movement from East African Rift System to Botswana Earthquake region.The Botswana Earthquake region is underlain by relatively thin crust(?40 km)and elevated heat flow(as the result of inflow of thermal fluid).Further,the Botswana Earthquake region show steep blocks of density anomalies,with the aftershocks clustering along a prominent NW-trending,NE-dipping density contrast separating a high-density(>2708 kg/m³)footwall and lower-density(2670-2700 kg/m³)hanging wall blocks.The region is also characterized by extensional forces predicted by local stress regime.Integration of the information led to suggestion that the Botswana Earthquake Region is a possible region of tectonic reactivation that came about due to multiple activities at play that could lead to future intraplate Earthquakes.In the final part of this thesis,in Chapter five(5),different theories of lunar crust evolution are proposed,which are based on the density distribution of crustal rocks.The density models show that lunar volcanism in the Rümker region exhibits different modes of emplacement.The Mons Rümker volcanic complex,that is located at the center of the Rümker region,is fed by an intrusion-like structure at a depth of?6-18 km that contains high-density basaltic materials of>3000 kg/m³.Conversely,Western and Eastern Rümker regions indicate a mantle source of volcanism,which were proposed to be fed by dikes.A quasi-circular mass anomaly(QCMA)with high gravity amplitude(?130 m Gal)and high density(>3000 kg/m³)represents deeper and thicker buried mare basalts with a bowl-shaped geometry formed by an impact event.The geophysical properties of the QCMA enable us to identify multiple impacts events in the Von Karman Crater that are partly responsible for mantle exposure on the surface of the South-Pole Aitken.The identification of possible source of lunar volcanism was integrated with geological and spectral data to develop a workable model for selection of a suitable landing and sampling area for future lunar missions,with specific and immediate application to the Chang‘E-5 sample return mission.To summarize,this thesis brings insight into the geodynamics of areas that were previously poorly constrained by seismic data.The three divisions of the thesis show how satellite-gravity data can be modeled into crustal thickness models and density models with limited prior information.The improvement of the geodynamic understanding of the selected areas on Earth and the Moon,especially in poorly covered by seismic studies will help us to better understand the geodynamics of the Earth and the Moon.