Poro-viscoelastic materials are well modelled with Biot-Allard equations. This model needs a number of geometrical parameters in order to describe the macroscopic geometry of the material and elastic parameters in order to describe the elastic properties of the material skeleton. Several characterisation methods of viscoelastic parameters of porous materials are studied in this thesis. Firstly, quasistatic and resonant characterization methods are described and analyzed. Secondly, a new inverse dynamic characterization of the same modulus is developed. The latter involves a two layers metal-porous beam, which is excited at the center. The input mobility is measured. The set-up is simplified compared to previous methods. The parameters are obtained via an inversion procedure based on the minimisation of the cost function comparing the measured and calculated frequency response functions (FRF). The calculation is done with a general laminate model. A parametric study identifies the optimal beam dimensions for maximum sensitivity of the inversion model. The advantage of using a code which is not taking into account fluid-structure interactions is the low computation time. For most materials, the effect of this interaction on the elastic properties is negligible. Several materials are tested to demonstrate the performance of the method compared to the classical quasi-static approaches, and set its limitations and range of validity. Finally, conclusions about their utilisation are given.

An empirically-based classification of lower Paleozoic carbonate-bearing rocks was created for field-based geotechnical applications. Geotechnical parameters were subsequently correlated to that classification. Seven hundred seventy-seven samples were used as the basis for the classification. Thirteen categories based on visual and tactile properties and a hydrochloric acid test were created. Samples were from central, north-central, and south-central Kentucky and represented the majority of Ordovician exposures in the state, and some Mississippian exposures. Few Silurian and Devonian units were included in the sample set. Geotechnical parameters, including density as well as elastic constants (shear and compression wave velocities, Poisson’s ratio, Young’s modulus, and shear modulus), were calculated for 113 representative samples from the classification. Compression strength testing was completed on 29 samples and the slake durability index was calculated for 18 samples. Testing values were correlated to the classification system in an attempt to use the classification as a predictive and comparative tool for geotechnical applications. Despite samples being heterogeneous and isotropic, each of the 13 categories behaved differently and predictably, with the sharpest contrast in siliciclastic and carbonate rocks.

A spherical wave AVO response is investigated by measuring ultrasonic reflection amplitudes from a water/Plexiglas interface. The experimental results show substantial deviation from the plane-wave reflection coefficients at large angles. However there is an excellent agreement between experimental data and full-wave numerical simulations performed with the reflectivity algorithm. By comparing the spherical-wave AVO response, modeled with different frequencies, to the plane-wave response, I show that the differences between the two are of such magnitude that three-term AVO inversion based on AVA curvature can be erroneous. I then propose an alternative approach to use critical angle information extracted from AVA curves, and show that this leads to a significant improvement of the estimation of elastic parameters. Azimuthal variation of the AVO response of a vertically fractured model also shows good agreement with anisotropic reflectivity simulations, especially in terms of extracted critical angles which indicated that (1) reflection measurements are consistent with the transmission measurements; (2) the anisotropic numerical simulation algorithm is capable of simulating subtle azimuthal variations with excellent accuracy; (3) the methodology of picking critical angles on seismograms using the inflection point is robust, even in the presence of random and/or systematic noise.

Orientador: Lucio Tunes Dos Santos / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica e Instituto de Geociências / Made available in DSpace on 2018-08-11T01:05:43Z (GMT). No. of bitstreams: 1 Grosfeld_Valeria_D.pdf: 2985169 bytes, checksum: 82ddf2042ee5ce573f870e3deebfa469 (MD5) Previous issue date: 2007 / Resumo: Neste trabalho estudamos os coeficientes de reflexão RPP e RPS para ondas elásticas. Introduzimos uma nova aproximação tipo impedância para o coeficiente RPS, baseados no êxito deste tipo de aproximações para o RPP na região de ângulos críticos e pós-críticos. Apesar de não ter-se mostrado tão eficiente quanto a aproximação tipo impedância de reflexão para RPP na região de interesse, se comparamos nossa aproximação com algumas já existentes, o comportamento é um pouco melhor que as aproximações precedentes. Esta análise foi feita mediante uma nova metodología, baseada em curvas de desempenho de algoritmos. Também mostramos que aproximando o coeficiente de reflexão RPP por uma aproximação tipo impedância é possível obter um indicador da presença de hidrocarbonetos sem necessidade de inverter os dados. Por outro lado discutimos como, com algumas hipóteses adicionais, se podem estimar alguns parâmetros elásticos das rochas diretamente dos dados. Por último, analisamos o efeito de parte do processamento sísmico na obtenção de nossas estimações em dados sintéticos / Abstract: In this work we are concerned with the reflection coefficients RPP and RPS for elastic waves. Based on the success of an impedance type approximation for the coefficient RPP in the critical region, we introduce a new approximation for the coefficient RPS. Although the new approximation was not so good as for the previous in the RPP case, comparing our approach with the existing ones we found that its behaviour is a little better than the preceding approaches. This comparison was made using a new methodology based on performace profile curves. Moreover, we show that, using the impedance type approximation for the reflection coeficient RPP , it is possible to get an indicator that reacts to the presence of hydrocarbons without the necessity of the invert the data. We also demostrate that under suitable conditions some elastic parameters of the rocks can be estimated directly from the data. Finally, we analyse the effect of seismic processing in order to obtain our estimate in synthetic data / Doutorado / Reservatórios e Gestão / Doutor em Ciências e Engenharia de Petróleo

En géomécanique, la caractérisation de l’état de contrainte et de la rhéologie d’un massif rocheux peut être obtenue en mesurant la réponse en déformation du terrain sous l’effet d’une sollicitation connue. Une méthode parmi d’autres consiste à recourir pour cela à une cellule de mesure intégrée (comportant des capteurs de déformation orientés selon différentes directions) installée dans un forage et rendue solidaire du massif par l’intermédiaire d’une colle époxy. Ce principe de mesure est utilisé, notamment, pour déterminer l’état de contraintes in situ par la méthode dite de « surcarottage » et les caractéristiques élastiques de la roche à partir de l’essai « biaxial ».Entre novembre 2005 et janvier 2006, une campagne d’essais géomécaniques de ce type a été menée dans l’argilite de Tournemire (Aveyron, France), à l’aide des cellules CSIRO. Les mesures de déformation obtenues ont révélé des phénomènes inhabituels qui ont rendu délicate la détermination des caractéristiques élastiques anisotropes de la roche et impossible l’accès aux contraintes du site.La présente thèse a pour objectif de contribuer, par la recherche d’explications à l’origine de ces phénomènes, d’une part, à l’amélioration de la connaissance du comportement de l’argilite de Tournemire et, d’autre part, à l’amélioration du protocole de mesure et d’interprétation de déformations obtenues par cellules CSIRO.Notre démarche consiste, dans un premier temps, à émettre un certain nombre d’hypothèses explicatives des phénomènes observés par la recherche bibliographique. Dans un deuxième temps, nous testons ces hypothèses à travers la modélisation analytique et numérique des essais de surcarottage et biaxiaux, puis à travers la réalisation de nouvelles expérimentations in situ et en laboratoire sur l’argilite, mais aussi sur des matériaux-tests (ciment, échantillon de colle).Nous concluons que les phénomènes inhabituels observés résultent, pour l’essentiel, des conditions de mise en œuvre in situ des cellules CSIRO. En particulier, nous mettons l’accent sur les artéfacts induits par le comportement visco-plastique de la colle époxy lorsqu’elle n’est pas parfaitement polymérisée. Le rôle de l’endommagement de la roche généré par les opérations de forage est également discuté. Nous en tirons des recommandations pratiques pour la réalisation de nouveaux essais dans des conditions similaires / In Geomechanics, determining the state of stress and the rheology of rock massive can be obtained by measuring the strain response of the ground under the effect of a known stress. A method among others is to use a cell integrated (with strain gauges oriented in different directions) installed in a borehole and secured to the mass through an epoxy glue. This measurement is used, notably, to determine the stress state in situ by the « overcoring » method and the elastic parameters of the rock from the « biaxial » test.Between November 2005 and January 2006, a geomechanical testing campaign was conducted in the argillaceous formation of the Tournemire experimental site (Aveyron, France) using CSIRO Hi cells. The strain measurements obtained during overcoring and biaxial tests, have shown unusual phenomena, which have made difficult the determination of anisotropic elastic parameters of the rock and the access to the site stress.Therefore, through researches for explanations of the origin of these phenomena, this thesis aims to improve and to contribute to the understanding of argillite Tournemire’s behaviour and to upgrade the measurement protocol as well as the interpretation of cells CSIRO’s strain.Our approach is, firstly, to issue a number of hypotheses to explain certain, phenomena observed in literature. In a second step, we test these hypotheses through analytical and numerical modelling of the biaxial and overcoring tests then through the realization of new experiments in situ within laboratory on argillite, and also on materials tests (cement, sample of glue).We conclude that the unusual phenomena observed are essentially the result of the conditions for implementing in situ CSIRO’s cell. In particular, we focus on the artefacts induced by the visco-plastic behaviour of the epoxy glue when it is incompletely polymerised. The role of damage on the rock generated by drilling operations is also discussed. We draw some practical recommendations for implementing new tests under similar conditions

L’objectif de ce travail est double : d’une part, il s’agit de développer une méthodologie intégrée pour la construction d’un modèle géomécanique ainsi que la représentation des incertitudes associées aux propriétés poro-élastiques des roches constitutives, en exploitant l’ensemble des données disponibles et en s’appuyant de façon cohérente sur les modèles de réservoir statique et dynamique classiquement utilisés par les géologues et les ingénieurs réservoir ; d’autre part, il s’agit d’analyser quel est l’impact des hétérogénéités géologiques, souvent négligées, dans la réponse mécanique du réservoir sollicité par son exploitation, et d’aboutir à des incertitudes sur les champs de contraintes et de déplacements, issues des incertitudes sur ces hétérogénéités et leurs paramètres mécaniques. Pour ce faire, une méthodologie intégrée s’appuyant sur des simulations géostatistiques a été développée. Après la construction du cadre géométrique 3D, le remplissage des propriétés au sein du réservoir suit une démarche de simulations géostatistiques 3D emboîtées, dans laquelle la représentation des hétérogénéités lithologiques conditionne la génération des propriétés poro-élastiques. La démarche consiste ensuite à représenter les incertitudes sur le modèle géomécanique par des ensembles de réalisations géostatistiques dont la réponse mécanique est alors calculée avec un simulateur mécanique aux éléments finis. Les incertitudes sur les champs de contraintes et de déformations sont déduites ensuite des différentes réponses mécaniques obtenues. La démarche a été mise en œuvre sur un réservoir réel, dans un environnement fluvio-deltaïque, produisant en Mer du Nord. Dans ce cadre, il a été démontré que les hétérogénéités du réservoir et leurs incertitudes influencent significativement les calculs des champs de contraintes et de déformations, ainsi que les risques mécaniques de rupture. Des incertitudes sur les quantités mécaniques analysées (premier invariant du tenseur des contraintes et subsidence) ont été aussi estimées / This work has two main objectives. The first one is to develop an integrated methodology allowing to build a 3D geomechanical model and also to image the uncertainties attached to the poro-mechanical properties of the constitutive rocks. This geomechanical model should be based on all related available data and should be consistent with the static and dynamic models, currently built by reservoir geologists and engineers. The second objective is to analyse the impact of geological heterogeneities, which are often neglected, in the mechanical response of the reservoir induced by its exploitation, and furthermore to derive uncertainties on the stress and deformation fields related to the uncertainties on the input properties of the geomechanical model. An integrated methodology based on geostatistical simulations is developed. First, the geometric frame is built; then an approach of embedded stochastic simulations is carried out to infill the different reservoir properties, the lithological description constraining the petrophysical and poro-elastic descriptions. The next step is to generate the mechanical responses of the stochastic realisations, using a finite-element mechanical simulator. The uncertainties on the resulting stress and displacement fields are then deduced from the multiple mechanical responses which are computed. This approach is demonstrated on a real field case, a fluvio-deltaic reservoir in North Sea. It is shown on this example that the reservoir heterogeneities and their uncertainties significantly influence the calculations of stress and strain fields, and also the risks of mechanical failure. Uncertainties on the mechanical quantities under analysis (first invariant of the stress tensor and subsidence) are also derived

Made available in DSpace on 2015-02-24T19:48:36Z (GMT). No. of bitstreams: 1 RobertoGO_Capa_ate_pag82.pdf: 4449318 bytes, checksum: a8a67621781bd4f76c4e2c0361bcc6a2 (MD5) Previous issue date: 2008-07-27 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / The Borborema Province (BP) is a geologic domain located in Northeastern Brazil. The BP is limited at the south by the S?o Francisco craton, at the west by the Parna?ba basin, and both at the north and east by coastal sedimentary basins. Nonetheless the BP surface geology is well known, several key aspects of its evolution are still open, notably: i)its tectonic compartmentalization established after the Brasiliano orogenesis, ii) the architecture of its cretaceous continental margin, iii) the elastic properties of its lithosphere, and iv) the causes of magmatism and uplifting which occurred in the Cenozoic. In this thesis, a regional coverage of geophysical data (elevation, gravity, magnetic, geoid height, and surface wave global tomography) were integrated with surface geologic information aiming to attain a better understanding of the above questions. In the Riacho do Pontal belt and in the western sector of the Sergipano belt, the neoproterozoic suture of the collision of the Sul domain of the BP with the Sanfranciscana plate (SFP) is correlated with an expressive dipolar gravity anomaly. The positive lobule of this anomaly is due to the BP lower continental crust uplifting whilst the negative lobule is due to the supracrustal nappes overthrusting the SFP. In the eastern sector of the Sergipano belt, this dipolar gravity anomaly does not exist. However the suture still can be identified at the southern sector of the Maranc? complex arc, alongside of the Porto da Folha shear zone, where the SFP N-S geophysical alignments are truncated. The boundary associated to the collision of the Cear? domain of the BP with the West African craton is also correlated with a dipolar gravity anomaly. The positive lobule of this anomaly coincides with the Sobral-Pedro II shear zone whilst the negative lobule is associated with the Santa Quit?ria magmatic arc. Judging by their geophysical signatures, the major BP internal boundaries are: i)the western sector of the Pernambuco shear zone and the eastern continuation of this shear zone as the Congo shear zone, ii) the Patos shear zone, and iii) the Jaguaribe shear zone and its southwestern continuation as the Tatajuba shear zone. These boundaries divide the BP in five tectonic domains in the geophysical criteria: Sul, Transversal, Rio Grande do Norte, Cear?, and M?dio Corea?. The Sul domain is characterized by geophysical signatures associated with the BP and SFP collision. The fact that Congo shear zone is now proposed as part of the Transversal domain boundary implies an important change in the original definition of this domain. The Rio Grande do Norte domain presents a highly magnetized crust resulted from the superposition of precambrian and phanerozoic events. The Cear? domain is divided by the Senador Pompeu shear zone in two subdomains: the eastern one corresponds to the Or?s-Jaguaribe belt and the western one to the Cear?-Central subdomain. The latter subdomain exhibits a positive ENE-W SW gravity anomaly which was associated to a crustal discontinuity. This discontinuity would have acted as a rampart against to the N-S Brasiliano orogenic nappes. The M?dio Corea? domain also presents a dipolar gravity anomaly. Its positive lobule is due to granulitic rocks whereas the negative one is caused by supracrustal rocks. The boundary between M?dio Corea? and Cear? domains can be traced below the Parna?ba basin sediments by its geophysical signature. The joint analysis of free air anomalies, free air admittances, and effective elastic thickness estimates (Te) revealed that the Brazilian East and Equatorial continental margins have quite different elastic properties. In the first one 10 km < Te < 20 km whereas in the second one Te ? 10 km. The weakness of the Equatorial margin lithosphere was caused by the cenozoic magmatism. The BP continental margin presents segmentations; some of them have inheritance from precambrian structures and domains. The segmentations conform markedly with some sedimentary basin features which are below described from south to north. The limit between Sergipe and Alagoas subbasins coincides with the suture between BP and SFP. Te estimates indicates concordantly that in Sergipe subbasin Te is around 20 km while Alagoas subbasin has Te around 10 km, thus revealing that the lithosphere in the Sergipe subbasin has a greater rigidity than the lithosphere in the Alagoas subbasin. Additionally inside the crust beneath Sergipe subbasin occurs a very dense body (underplating or crustal heritage?) which is not present in the crust beneath Alagoas subbasin. The continental margin of the Pernambuco basin (15 < Te < 25 km) presents a very distinct free air edge effect displaying two anomalies. This fact indicates the existence in the Pernambuco plateau of a relatively thick crust. In the Para?ba basin the free air edge effect is quite uniform, Te ? 15 km, and the lower crust is abnormally dense probably due to its alteration by a magmatic underplating in the Cenozoic. The Potiguar basin segmentation in three parts was corroborated by the Te estimates: in the Potiguar rift Te ? 5 km, in the Aracati platform Te ? 25 km, and in the Touros platform Te ? 10 km. The observed weakness of the lithosphere in the Potiguar rift segment is due to the high heat flux while the relatively high strength of the lithosphere in the Touros platform may be due to the existence of an archaean crust. The Cear? basin, in the region of Munda? and Icara? subbasins, presents a quite uniform free air edge effect and Te ranges from 10 to 15 km. The analysis of the Bouguer admittance revealed that isostasy in BP can be explained with an isostatic model where combined surface and buried loadings are present. The estimated ratio of the buried loading relative to the surface loading is equal to 15. In addition, the lower crust in BP is abnormally dense. These affirmations are particularly adequate to the northern portion of BP where adherence of the observed data to the isostatic model is quite good. Using the same above described isostatic model to calculate the coherence function, it was obtained that a single Te estimate for the entire BP must be lower than 60 km; in addition, the BP north portion has Te around 20 km. Using the conventional elastic flexural model to isostasy, an inversion of crust thickness was performed. It was identified two regions in BP where the crust is thickened: one below the Borborema plateau (associated to an uplifting in the Cenozoic) and the other one in the Cear? domain beneath the Santa Quit?ria magmatic arc (a residue associated to the Brasiliano orogenesis). On the other hand, along the Cariri-Potiguar trend, the crust is thinned due to an aborted rifting in the Cretaceous. Based on the interpretation of free air anomalies, it was inferred the existence of a large magmatism in the oceanic crust surrounding the BP, in contrast with the incipient magmatism in the continent as shown by surface geology. In BP a quite important positive geoid anomaly exists. This anomaly is spatially correlated with the Borborema plateau and the Maca?-Queimadas volcanic lineament. The integrated interpretation of geoid height anomaly data, global shear velocity model, and geologic data allow to propose that and Edge Driven Convection (EDC) may have caused the Cenozoic magmatism. The EDC is an instability that presumably occurs at the boundary between thick stable lithosphere and oceanic thin lithosphere. In the BP lithosphere, the EDC mechanism would have dragged the cold lithospheric mantle into the hot asthenospheric mantle thus causing a positive density contrast that would have generated the main component of the geoid height anomaly. In addition, the compatibility of the gravity data with the isostatic model, where combined surface and buried loadings are present, together with the temporal correlation between the Cenozoic magmatism and the Borborema plateau uplifting allow to propose that this uplifting would have been caused by the buoyancy effect of a crustal root generated by a magmatic underplating in the Cenozoic / A Prov?ncia Borborema (PB) ? um dom?nio geol?gico-estrutural localizado no Nordeste do Brasil, limitado a sul pelo Cr?ton do S?o Francisco, a oeste pela Bacia do Parna?ba e a norte e leste pelas bacias costeiras. Embora bastante estudada por geologia de superf?cie, na PB ainda est?o em aberto aspectos importantes de sua evolu??o, notadamente: i) a sua compartimentagem tect?nica ap?s a Orog?nese Brasiliana, ii) a arquitetura da margem continental implantada no Cret?ceo, iii) as propriedades el?sticas de sua litosfera, e iv) as causas do magmatismo e do soerguimento no Cenoz?ico. Esta Tese empregou dados geof?sicos de cobertura regional (eleva??o, gravimetria, magnetometria, altura geoidal e tomografia), para aportar informa??es de geologia profunda aos problemas acima colocados. A sutura gerada pela colis?o neoproteroz?ica entre o Dom?nio Sul da PB e a Placa Sanfranciscana (PSF) ? marcada, na Faixa Riacho do Pontal e no oeste da Faixa Sergipana, por uma forte anomalia gravim?trica dipolar, cujo pico positivo corresponde ao al?amento da crosta inferior da PB e o negativo corresponde ?s nappes de supracrustais empurradas sobre a PSF. Na regi?o leste da Faixa Sergipana n?o h? assinaturas gravim?tricas que indiquem cavalgamento e flexura de placas, mas a interpreta??o de truncamentos de assinaturas geof?sicas de dire??o N-S da PSF permite localizar a sutura na margem sul do complexo de arco Maranc?, ao longo da Z. C. Porto da Folha. Por sua vez, o limite colisional do Dom?nio Cear? da PB com o Cr?ton Oeste-Africano, ao longo da Z. C. Sobral-Pedro II, ? tamb?m marcado por uma anomalia gravim?trica dipolar, cujo pico positivo coincide com a Z. C. Sobral-Pedro II, e o negativo coincide com o arco magm?tico de Santa Quit?ria. A julgar pela express?o geof?sica, os limites internos mais importantes da PB s?o: i) a Z. C. Pernambuco Oeste e sua continua??o na Z. C. Congo, ii) a Z. C. Patos e iii) a Z. C. Jaguaribe e sua continua??o na Z. C. Tatajuba. Estes limites dividem a PB em cinco grandes dom?nios geof?sicos-tect?nicos: Sul (ou Externo), Transversal, Rio Grande do Norte, Cear? e M?dio Corea?. O Dom?nio Sul ? marcado por assinaturas geof?sicas associadas ? colis?o da PB com a PSF. O Dom?nio Transversal teve a sua concep??o original de limites modificada porque a parte leste do seu limite sul foi associada com a Z. C. Congo. O Dom?nio Rio Grande do Norte apresenta a crosta mais magn?tica da PB, com superposi??o de fontes pr?-cambrianas e faneroz?icas. No Dom?nio Cear?, a Z. C. Senador Pompeu ? o divisor de dois subdom?nios: o leste corresponde ? Faixa Or?s-Jaguaribe e o oeste corresponde ao Cear?-Central, onde ocorre uma assinatura gravim?trica interpretada como uma descontinuidade crustal de dire??o ENE-WSW, que funcionou como um anteparo para as nappes brasilanas, com sentido de deslocamento para sul. O Dom?nio M?dio Corea? apresenta uma anomalia gravim?trica dipolar, cujo pico positivo est? associado com rochas granul?ticas, e o negativo com rochas supracrustais. A assinatura geof?sica do seu limite com o Dom?nio Cear? ? evidente, apesar dos sedimentos da Bacia do Parna?ba. A an?lise conjunta da anomalia ar-livre, admit?ncia ar-livre e estimativas da espessura el?stica efetiva (Te) evidenciou que as margens Leste e Equatorial possuem propriedades el?sticas bastante diferentes: enquanto a primeira tem Te entre 10 e 20 km, a segunda tem Te em torno ou inferior a 10 km. Essa diferen?a ? devida ao enfraquecimento da litosfera da Margem Equatorial produzida pelo magmatismo cenoz?ico. A margem continental da PB apresenta segmenta??es que incorporaram heran?as das estruturas e dos dom?nios pr?-cambrianos, que se correlacionam com os limites conhecidos das bacias. Descrevendo de sul para norte, o limite da separa??o da Bacia Sergipe - Alagoas em duas sub-bacias coincide com a sutura entre o Dom?nio Sul da PB e a PSF; as estimativas de Te indicam, concordantemente, que a Sub-bacia Sergipe (Te ? 20 km) se instalou em uma litosfera mais resistente do que a da Sub-bacia Alagoas (Te ? 10 km). Adicionalmente, no interior da crosta da Sub-bacia Sergipe ocorre um grande corpo denso (underplating ou heran?a crustal?) que n?o continua na Sub-bacia Alagoas. A margem da Bacia de Pernambuco (15 < Te < 25 km) apresenta caracter?sticas diferentes das outras bacias costeiras, porque no Plat? de Pernambuco h? duas anomalias do efeito de borda , o que indica a exist?ncia no plat? de uma crosta continental afinada, contudo ainda relativamente espessa. A Bacia da Para?ba se apresenta bastante uniforme, com Te em torno de 15 km, e possui uma crosta inferior relativamente densa, que foi interpretada como uma modifica??o por underplating magm?tico relacionado com o magmatismo cenoz?ico. A segmenta??o da Bacia Potiguar em tr?s partes ? corroborada pelas estimativas de Te: Rifte Potiguar (Te ? 5 km), Plataforma de Aracati (Te ? 25 km) e Plataforma de Touros (Te ? 10 km). A fragilidade da litosfera na regi?o do Rifte Potiguar est? associada com fluxo t?rmico atual alto, e a resist?ncia relativamente maior da Plataforma de Touros pode ser devida a uma crosta arqueana. A margem da Bacia do Cear?, no trecho das sub-bacias Munda? e Icara?, possui anomalia ar-livre uniforme, com Te entre 10 e 15 km. A an?lise da admit?ncia Bouguer revelou que a condi??o isost?tica da PB ? compat?vel com um modelo em que ocorrem carregamentos combinados na superf?cie e na base da crosta, com a carga da base 15 vezes maior que a do topo. Em adi??o, a PB possui uma crosta inferior anormalmente densa. Estas afirma??es s?o especialmente adequadas para a parte norte da PB porque a? a ader?ncia dos dados observados ao modelo ? maior. Para o mesmo modelo isost?tico e usando a fun??o coer?ncia, estimou-se que a Te da PB deve ser inferior a 60 km, embora sua por??o norte tenha Te de apenas 20 km. A invers?o de espessura de crosta, usando o modelo isost?tico com carga apenas na superf?cie, indicou que existem na PB duas regi?es de espessamento: uma abaixo do Planalto da Borborema (de origem cenoz?ica) e a outra no Dom?nio Cear?, sob o arco magm?tico de Santa Quit?ria (vestigial do Pr?-cambriano). Por outro lado, ocorre um afinamento ao longo do Trend Cariri-Potiguar, que representa o registro no interior do continente de um rifteamento cret?ceo abortado. A interpreta??o das anomalias ar-livre de fontes oce?nicas levou ? proposi??o de que ocorreu um volumoso magmatismo na ?rea oce?nica adjacente ? PB, ao contr?rio da ?rea continental, como indicam as informa??es de geologia de superf?cie. A PB apresenta uma expressiva anomalia positiva de ge?ide, com correla??o espacial com o Planalto da Borborema e o Alinhamento Macau-Queimadas. A integra??o de dados de tomografia de ondas superficiais e de anomalias residuais de ge?ide permitiu interpretar que uma convec??o em pequena escala (Edge Driven Convection-EDC), gerada na interface entre a raiz da litosfera continental fria e o manto quente da ?rea oce?nica, pode ter sido a causa do magmatismo cenoz?ico. O mecanismo de EDC teria causado o arrasto do manto litosf?rico continental frio para dentro do manto astenosf?rico quente, ocasionando assim contraste positivo de densidade, que seria uma componente importante da origem da anomalia de ge?ide. A compatibilidade dos dados gravim?tricos da PB com o modelo isost?tico que combina carregamentos no topo e na base da crosta, e a correla??o temporal entre o magmatismo cenoz?ico e o soerguimento do planalto, permite propor que o soerguimento deste ocorreu por causa do empuxo provocado pela raiz da crosta, produzida por um underplating magm?tico no Cenoz?ico