Resolution test of GOCE satellite data applied to density anomalies at crustal and upper mantle levels

The Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite mission was devised by the European Space Agency to study the Earth’s gravity field with an unprecedented accuracy using gravity gradient data. The goal of this study is to analyze the resolution in terms of size, burial depth and density contrast of anomalous bodies related to geological structures that can be identified from GOCE data. A parametric study is performed by calculating the gravity gradients associated with rectangular prisms with fixed aspect ratio of 9:3:1 and varying the size, burial depth, and density contrast, selecting those structures showing amplitudes and wavelength variations comparable to the accuracy of GOCE data. Results show that the minimum size for crustal anomalies to be resolved for the vertical component of the gravity gradient is 22.5x7.5x2.5km for a Δρ=500kg/m3 , burial depth of 0km, and at computation height of 255km. To generate a sufficient signal in amplitude and wavelength in all the components, the size of the anomalous body is 270x90x30km. For a body with Δρ=50kg/m3 and 0km burial depth a minimum size of 41.4x13.8x4.6km is required for the vertical component at a computation height of 255km. In addition, the application to the 3D case of a passive continental margin which broadly resembles the crustal structure of the NW-Iberia shows that the signal of all gravity gradient components is dominated by the crustal thinning associated with the passive continental margins and the corresponding isostatic response

Efficient 3-D Large-Scale Forward Modeling and Inversion of Gravitational Fields in Spherical Coordinates With Application to Lunar Mascons

A novel efficient forward modeling algorithm of gravitational fields in spherical coordinates is developed for 3D large-scale gravity inversion problems. 3D Gauss-Legendre quadrature (GLQ) is used to calculate the gravitational fields of mass distributions discretized into tesseroids. Equivalence relations in the kernel matrix of the forward-modeling are exploited to decrease storage and computation time. The numerical investigations demonstrate that the computation time of the proposed algorithm is reduced by approximately two orders of magnitude, and the memory requirement is reduced by N'l times compared with the traditional GLQ method, where N'l is the number of model elements in the longitudinal direction. These significant improvements in computational efficiency and storage make it possible to calculate and store the dense Jacobian matrix in 3D large-scale gravity inversions. The equivalence relations could be equally applied to the Taylor series method or combined with the adaptive discretization to ensure high accuracies

Resolution test of GOCE satellite data applied to density anomalies at crustal and upper mantle levels

The GOCE satellite mission was devised by the European Space Agency to study the Earthâs gravity field with an unprecedented accuracy using gravity gradient data. The goal of this study is to analyze the resolution in terms of shape, minimum size, and density contrast of anomalous bodies related to geological structures that can be identified from GOCE data. A parametric study is performed by calculating the gravity gradients associated with rectangular prisms with fixed aspect ratio of 9:3:1 and varying the size, burial depth, and density contrast, selecting those structures showing amplitudes and wavelength variations comparable to the accuracy of GOCE data. Results show that the minimum size for crustal anomalies to be resolved is 270 x 90 x 30km for a Dr = 500kg/m3, burial depth of 0km, and a computation height of 255km. A minimum size of 585 x 195 x 65km is required for a body with Dr = 50kg/m3 and 200km burial depth. In addition, the application to the 3D case of a passive continental margin than resembles, in its main general trend, the crustal structure of the NW-Iberia shows that the signal of all gravity gradient components is dominated by the crustal thinning associated with the passive continental margins and the corresponding isostatic response

3-D multiobservable probabilistic inversion for the compositional and thermal structure of the lithosphere and upper mantle: III. Thermochemical tomography in the Western-Central U.S.

Acknowledgments We are indebted to F. Darbyshire and J. von Hunen for useful comments on earlier versions of this work. This manuscript benefited from thorough and constructive reviews by W. Levandowski and an anonymous reviewer. We also thank J. Connolly, M. Sambridge, B. Kennett, S. Lebedev, B. Shan, U. Faul, and M. Qashqai for insightful discussions about, and contributions to, some of the concepts presented in this paper. The work of J.C.A. has been supported by two Australian Research Council Discovery grants (DP120102372 and DP110104145). Seismic data are from the IRIS DMS. D.L.S. acknowledges support from NSF grant EAR-135866. This is contribution 848 from the ARC Centre of Excellence for Core to Crust Fluid Systems (http://www.ccfs.mq.edu.au) and 1106 in the GEMOC Key Centre (http://www.gemoc.mq.edu.au).Peer reviewedPublisher PD

Efficient 3D large-scale forward-modeling and inversion of gravitational fields in spherical coordinates with application to lunar mascons

An efficient forward modeling algorithm for calculation of gravitational fields in spherical coordinates is developed for 3D large‐scale gravity inversion problems. 3D Gauss‐Legendre quadrature (GLQ) is used to calculate the gravitational fields of mass distributions discretized into tesseroids. Equivalence relations in the kernel matrix of the forward‐modeling are exploited to decrease storage and computation time. The numerical tests demonstrate that the computation time of the proposed algorithm is reduced by approximately two orders of magnitude, and the memory requirement is reduced by N'λ times compared with the traditional GLQ method, where N'λ is the number of the model elements in the longitudinal direction. These significant improvements in computational efficiency and storage make it possible to calculate and store the dense Jacobian matrix in 3D large‐scale gravity inversions. The equivalence relations can be applied to the Taylor series method or combined with the adaptive discretization to ensure high accuracy. To further illustrate the capability of the algorithm, we present a regional synthetic example. The inverted results show density distributions consistent with the actual model. The computation took about 6.3 hours and 0.88 GB of memory compared with about a dozen days and 245.86 GB for the traditional 3D GLQ method. Finally, the proposed algorithm is applied to the gravity field derived from the latest lunar gravity model GL1500E. 3D density distributions of the Imbrium and Serenitatis basins are obtained, and high‐density bodies are found at the depths 10‐60 km, likely indicating a significant uplift of the high‐density mantle beneath the two mascon basins.</p

Cálculo y análisis de atributos de curvatura mediante mediciones de gradiente de gravedad de la misión satelital GOCE

El objetivo de este trabajo es calcular distintos atributos de curvatura mediante los datos de gradiente de gravedad obtenidos por la misión satelital GOCE, de la Agencia Espacial Europea. Estos atributos fueron calculados para Sudamérica, África, los Himalayas y Canadá, dado que son regiones que presentan rasgos geológicos particulares por la presencia de cordilleras (de distinta génesis), cratones y grandes áreas planas. Primero se hizo un análisis de la información disponible y cómo fue adquirida, de manera de conocer cómo está referenciada para poder manipularla correctamente. Luego se describe el marco teórico del procesamiento de los datos, el cual se realizó mediante la implementación de teseroides, para pasar finalmente al cálculo de los atributos de curvatura y su interpretación. Se calcularon los atributos mediante los datos satelitales y mediante datos sintéticos, de manera de realizar un contraste entre ambos y obtener conclusiones en base a las diferencias. Estos cálculos pusieron en evidencia el potencial de los atributos de curvatura calculados mediante los datos satelitales de GOCE, mostrando cómo varían según la región en que se los calcule y cómo pueden relacionarse (y diferenciarse) regiones con características similares mediante ellos. Además, se plantea el potencial del Shape Index como parámetro de relevancia en la mejora de modelos isostáticos en dorsales oceánicas.Facultad de Ciencias Astronómicas y Geofísica

Processing and Inversion of Airborne Gravity Gradient Data

In this thesis, a data-driven method for determining and reducing noise in AGG data will be presented first. The new noise reduction method is based on the idea of iteratively projecting survey data onto a lower level, upward continuing the data back to the original survey height, and then subtracting the upward continued data from the survey data. This method is successfully applied to the AGG data over Karasjok, Norway. The results show that the new noise reduction method can detect and reduce some high-frequency noise. Next, a fast equivalent source approach based on Landweber iteration and Gauss-FFT is developed. By applying the method to a synthetic dataset, the method shows great efficiency. Subsequently, two applications to real data over Karasjok are presented. The first is to jointly denoise the data with carefully selected parameters. The results are comparable to the routinely processed data which represents the industry standard. The second is to estimate densities of the topography in Karasjok with the data. The results show that the estimation method is a fast way to acquire an overview of densities of topography when only sparse petrophysical samples are available. At last, to obtain detailed density distributions of the survey area and evaluate the possibilities for mineralization, a stochastic inversion constrained by a prior lithology model and petrophysical data is applied to the AGG data. By inverting various combinations of AGG components, the results suggest that noise reduction prior to inversion is not necessary when the existing noise level is low and behaves like zero-mean Gaussian noise. The results also indicate that the constructed and the measured components both can be used for inversion and the inclusion of more than four components in the inversion does not provide additional information. From the acquired density models, insights into potential mineralization in the Karasjok area are provided

GOCE Gradiometer Measurement Disturbances and their Modelling by Means of Ionospheric Dynamics

We examine the presence of residual non-gravitational signatures in gravitational gradients measured by GOCE Electrostatic Gravity Gradiometer. These signatures are observed over the geomagnetic poles during geomagnetically active days and contaminate the trace of the Gravitational Gradient Tensor by up to three to five times the expected noise level of the instrument (11 mE). We investigate these anomalies in the gradiometer measurements along many satellite tracks and examine possible causes by using external datasets, such as Interplanetary Electric Field observations from the ACE (Advanced Composition Explorer) and WIND spacecraft and Poynting flux (vector) estimated from Equivalent Ionospheric Currents derived from Spherical Elementary Current Systems over North America and Greenland. We show that the variations in the east-west and vertical electrical currents and Poynting flux (vector) components at the satellite position are highly correlated with the disturbances observed in the gradiometer measurements. We identify the relation between the ionospheric dynamics and disturbances and develop a data-driven model to reduce the effects of these disturbances. The results presented in this dissertation discover that the cause of the disturbances are due to intense ionospheric dynamics that are enhanced by increased solar activity which causes a dynamic drag environment. Moreover, using external information about the ionospheric dynamics, we successfully model and remove a high percentage of these disturbances for the first time in GOCE literature and promise improved data for future gravitational field models and studies of the Earth's upper atmosphere

Crustal and (sub)lithospheric structure beneath the Iranian Plateau from geophysical modeling

The thesis presents a geophysical study of the Iranian Plateau and the surrounding regions in order to understand the crustal and upper mantle structure. First, I present a study on the depth to basement and magnetic crustal domains beneath the Iranian Plateau by modeling aeromagnetic and gravity data. Inverse modeling of aeromagnetic data was carried out to estimate the depth to basement. Hereby, different magnetic domains in the uppermost crust (10-20 km depths) could be identified, which influence the medium to long wavelength trends of the magnetic anomalies. Next, the 3D crustal and upper mantle structure of Iran is investigated through integrated geophysical-petrological modeling combining elevation, gravity potential field, seismic data and petrological data. While tectonics and mantle xenolith suggest composition heterogeneities in the lithospheric mantle beneath Iranian Plateau, distinct mantle compositions are also required to make the model predictions and geophysical observables compatible. Sub-lithospheric sources have been disregarded in the initial model and I explore in the last step the effect of sub-lithospheric heterogeneities that might represent the remnants of a Neo-Tethys slab by adding a cold and fast body in the sub-lithosphere. My (sub)lithospheric thermochemical model structure provides synthetic seismic velocities comparable to model of Neo-Tethys slab break-off