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A large part of the recent oil discoveries in the world is linked to the Brazilian Pre-Salt, and part of the mapped giant/supergiant reservoirs are found in the Campos basin at the Brazilian eastern continental margin. The onshore part of this basin is bordered by the Ribeira Orogenic Belt (ROB), which represents a NE–SW trending system controlled by sliding shear belts, reactivated during its evolution since the Paleoproterozoic. Crustal thermal models have been developed to examine the implications of the observed intracratonic variations on heat flow and thus build an understanding of the geodynamic parameters of basin formation. The geothermal database used in this modeling includes direct and indirect measurements, and was expanded with over 56 locations, providing a spatial extent of 0.5 x 0.5 degrees in the continental part of the basin. The thermal model took into account the variation of thermal conductivity with temperature, as well as the variation of radiogenic heat generation with depth. Results show high values for the heat flow (>70mW/m2) in the region of the Quadrilátero Ferrífero in the southern part of São Francisco Craton, surrounded by moderate heat flow pattern but increasing significantly in offshore regions where the crustal thickness is much smaller (aprox. 25km). Results of the crustal thermal model integrated with multiphysics (gravity, magnetic and seismic) datasets generate tools for imaging deep structures, especially in the distal portion of the Campos Basin, and map potential basement paleo highs and intrusive magmatic/volcanic features possibly associated to hydrocarbon and geothermal prospects., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

We have used magnetotelluric data imaging to determine the resistivity structure across southern Kenya and our results suggest the presence of a buckled blocky or segmented lithosphere across the region. Prominent steep conductive zones at the Oloololo (OLO) escarpment and eastern rift margin allow us to subdivide the region into three crustal domains. West of OLO, a bow-shaped conductor underlies a 10 km thick resistive upper crustal unit spatially correlating with an exposed Archaean greenstone belt. Between OLO and the eastern rift margin are found steeply dipping alternating conductive and resistive zones that appear buckled. East of this belt are found prominent, 5 to 20 km deep, subhorizontal conductors atop steep resistive blocks with flanking conductors. The main steep features in the crust appear to extend below the seismic Moho and thus suggest the presence of anomalously thick crust across the region. A 50 km-wide and 4–8 km deep w-shaped (double half-graben) structure is suggested at the position of the Kenyan rift. We show that our inferred lateral zoning is consistent with collocated gravity and seismic measurements. We propose a link between the deep resistivity heterogeneity and surface deformation pattern in the area.

Accurate interpretation of magnetotelluric (MT) data in the presence of static shift arising from near-surface inhomogeneities is an unresolved problem in three-dimensional (3-D) inversion. While it is well known in 1-D and 2-D studies that static shift can lead to erroneous interpretation, how static shift can influence the result of 3-D inversion is not fully understood and is relevant to improved subsurface analysis. Using the synthetic data generated from 3-D models with randomly distributed heterogeneous overburden and elongate homogeneous overburden that are consistent with geological observations, this paper examines the effects of near-surface inhomogeneity on the accuracy of 3-D inversion models. It is found that small-scale and shallow depth structures are severely distorted while the large-scale structure is marginally distorted in 3-D inversion not accounting for static shift; thus the erroneous near-surface structure does degrade the reconstruction of smaller-scale structure at any depth. However, 3-D joint inversion for resistivity and static shift significantly reduces the artifacts caused by static shifts and improves the overall resolution, irrespective of whether a zero-sum or Gaussian distribution of static shifts is assumed. The 3-D joint inversion approach works equally well for situations where the shallow bodies are of small size or long enough to allow some induction such that the effects of near-surface inhomogeneity are manifested as a frequency-dependent shift rather than a constant shift.

Tese de doutoramento, Ciências Geofísicas e da Geoinformação (Geofísica), Universidade de Lisboa, Faculdade de Ciências, 2012 Submitted by amelia Janeiro (ajaneiro@reitoria.ul.pt) on 2012-11-16T11:54:14Z No. of bitstreams: 1 ulsd063907_td_Rui_Goncalves.pdf: 20446397 bytes, checksum: a8c4e106d10133ffafd03aac58335168 (MD5) Made available in DSpace on 2012-11-16T14:31:26Z (GMT). No. of bitstreams: 1 ulsd063907_td_Rui_Goncalves.pdf: 20446397 bytes, checksum: a8c4e106d10133ffafd03aac58335168 (MD5) Previous issue date: 2012 Fundação para a Ciência e a Tecnologia (FCT, SFRH/BD/24640/2005 e projeto HYDROARID-POCI/CTE/GEX/55399/ 2004)

The presented thesis deals with the multi-dimensional reconstruction of the earth's conductivity distribution based on DC resistivity data. This task represents a nonlinear and ill-posed minimization problem with many degrees of freedom. In this work, techniques for regularization and controlling of this problem are depicted and classified. Particularly, it is concentrated on explicit regularization types, which impose constraints onto the model. The system of equations as resulting from the application of the Gauss-Newton minimization can be solved efficiently. Furthermore, it is shown how the regularization strength can be controlled. The method of non-linear resolution analysis plays a central role in the thesis. It represents a powerful tool to estimate the quality of inversion results. Furthermore, the derived resolution measures provide the basis for the optimization of experimental design concerning information content and efficiency. Methods of error estimation, forward modeling and the calculation of the Jacobian matrix for DC resistivity data are developed. Procedures for appropriate parameterization and inversion control are pointed out by studies of synthetic models. Different inversion and regularization methods are examined in detail. A linearized study is used to compare different data sets considering their efficiency. Moreover, a triplegrid-technique for the incorporation of topography into three-dimensional inversion is presented. Finally the inversion methods are applied to field data. The depicted optimization strategies are realized in practice, which increases the economic relevance of threedimensional data acquisition. The structure of the subsurface is imaged in detail for several applications in the fields of cavity detection, archaeology and the investigation of ground falls. The resolution analysis is successfully established to appraise the obtained results.