Peter Lelievre

Peter Lelievre
Mount Allison University · Department of Mathematical and Computer Science

PhD Geophysics

About

58
Publications
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1,076
Citations

Publications

Publications (58)
Article
Full-text available
Scanning magnetic microscopy (SMM) is a modern magnetometry technique that maps the magnetic anomalies resulting from small‐scale variations of remanent magnetization within a sample. This information is vital to understand the origin of rock behavior in laboratory experiments and in larger scale magnetic surveys. To quantify the fine‐scale remanen...
Presentation
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3D Image reconstruction with Deep Learning AI on hi resolution drone magnetometer
Article
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Seafloor massive sulfide deposits form in remote environments, and the assessment of deposit size and composition through drilling is technically challenging and expensive. To aid the evaluation of the resource potential of seafloor massive sulfide deposits, three-dimensional inverse modeling of geophysical potential field data (magnetic and gravit...
Conference Paper
Full-text available
We present a general scheme for 3D geophysical inversion using a deep learning convolutional neural network that enables three-dimensional inversions of useful size to be solved on laptops and desktops. A priori constraints of maximum smoothness or compactness on model parameters used during conventional geophysical inversion are not necessary. In...
Article
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Imaging the internal structure of volcanoes helps highlighting magma pathways and monitoring potential structural weaknesses. We jointly invert gravimetric and muographic data to determine the most precise image of the 3D density structure of the Puy de Dôme volcano (Chaîne des Puys, France) ever obtained. With rock thickness of up to 1,600 m along...
Article
Magnetic and gravity data are used in the early stages of exploration for uranium deposits in the Athabasca Basin of Canada, just as for many other mineral exploration scenarios. Uranium mineralization in the Athabasca Basin is located where faults in the basement intersect the unconformity between the basement and the overlying sandstones. Both th...
Article
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Hydrothermal fluid circulation beneath the seafloor is an important process for chemical and heat transfer between the solid Earth and overlying oceans. Discharge of hydrothermal fluids at the seafloor supports unique biological communities and can produce potentially valuable mineral deposits. Our understanding of the scale and geometry of subseaf...
Article
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Geologists’ interpretations about the Earth typically involve distinct rock units with contacts between them. 3D geological models typically comprise surfaces of tessellated polygons that represent the contacts. In contrast, geophysical inversions are typically performed on voxel meshes comprising space-filling elements. Standard minimum-structure...
Article
Gravity signatures from features associated with the footprints of uranium deposits within the sandstones and basement of the Athabasca Basin are masked in the measured gravity by the contribution from glacial sediments (overburden), in particular by the variable thickness of the overburden. 2D inversions of seismic refraction and gravity data are...
Article
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Reduction to pole and other transformations of total field magnetic intensity data are often challenging to perform at low magnetic latitudes, when remanent magnetization exists, and when large topographic relief exists. Several studies have suggested use of inversion‐based equivalent source methods for performing such transformations under those c...
Article
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S U M M A R Y Gravimetry is a technique widely used to image the structure of the Earth. However, inversions are ill-posed and the imaging power of the technique rapidly decreases with depth. To overcome this limitation, muography, a new imaging technique relying on high energy atmospheric muons, has recently been developed. Because muography only...
Article
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Muography is a relatively new geophysical imaging method that uses muons to provide estimates of average densities along particular lines of sight. Muography can only see above the horizontal elevation of the detector and it is therefore attractive to attempt a joint inversion of muography data with gravity data, which is also responsive to density...
Article
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The creation of 3D models is commonplace in many disciplines. Models are often built from a collection of tessellated surfaces. To apply numerical methods to such models it is often necessary to generate a mesh of space-filling elements that conforms to the model surfaces. While there are meshing algorithms that can do so, they place restrictive re...
Article
We have developed a multiple level-set method for simultaneous inversion of gravity and seismic traveltime data. The method recovers the boundaries between regions with distinct physical properties assumed constant and known, creating structurally consistent models of two subsurface properties: P-wave velocity and density. In single level-set metho...
Article
Quantitative morphometric analyses of form are widely used in palaeontology, especially for taxonomic and evolutionary research. These analyses can involve several measurements performed on hundreds or even thousands of samples. Performing measurements of size and shape on large assemblages of macro- or microfossil samples is generally infeasible o...
Article
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This paper is concerned with the applicability of Pareto Multi-Objective Global Optimization (PMOGO) algorithms for solving different types of geophysical inverse problems. The standard deterministic approach is to combine the multiple objective functions (i.e. data misfit, regularization and joint coupling terms) in a weighted-sum aggregate object...
Conference Paper
Geologists' interpretations about the Earth typically involve distinct rock units with contacts between them. In contrast, standard minimum-structure mesh-based inversions recover smooth models inconsistent with such interpretations. We are researching a fundamentally different type of inversion that parameterizes the Earth in terms of contact surf...
Conference Paper
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The standard deterministic approach to joint inversion is to combine the multiple objectives (data misfits, regularization and joint coupling terms) into a weighted sum (aggregate) and minimize using a descent-based method. This approach has some disadvantages: appropriate weights must be determined for the aggregate, the use of local optimization...
Chapter
Many joint and cooperative inversion approaches have been applied to mineral exploration problems with varying levels of success but typically performing better than individual independent inversions. The geological scenarios encountered in mineral exploration are varied and complicated. This chapter demonstrates the great potential offered by inte...
Conference Paper
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Geological mapping in remote areas or in areas with limited out crop exposure can be a challenging and expensive endeavour. The development of predictive pseudo-geological maps from remote sensing data which make an educated guess at the potential lithological distribution in a region may present a potential avenue by which these challenges could b...
Article
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Joint inversion, the inversion of multiple geophysical data sets containing complementary information about the subsurface, has the potential to significantly improve inversion results by reducing the nonuniqueness of the inverse problem. One of the challenges of joint inversion is deciding how to couple the multiple physical property models. If a...
Article
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Using unstructured tetrahedral meshes to specify 3D geophysical Earth models has a numer of advantages. Such meshes can conform exactly to the triangularly tessellated wireframe surfaces in the 3D Earth models used by geologists. This offers up the possibility ofboth geophysicists and geologists working with a single unified Earth model. Unstructur...
Article
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The non-uniqueness of the underdetermined inverse problem requires that any available geological information be incorporated to constrain the results. Such information commonly comes in the form of a geological model comprising unstructured wireframe surfaces. Hence, we perform geophysical modelling on unstructured meshes, which provide the flexibi...
Article
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Gravity methods have long been used in mineral exploration. However, gravity methods have difficulty resolving small details. Seismic methods provide high resolving potential for use in mineral exploration. However, complicated hard-rock geology can make seismic data processing and interpretation difficult. By jointly inverting seismic tomography...
Article
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The underdetermined geophysical inverse problem is inherently non-unique, requiring additional information to recover geologically interpretable solutions. This additional information commonly includes petrophysical and structural measurements. It can also involve 3D geological Earth models, e.g. ore deposit models commonly created during delineati...
Conference Paper
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Conference Paper
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To be reliable, Earth models used for mineral exploration, or other subsurface investigations, should be consistent with all available geological and geophysical information. Geophysical inversion provides the means to integrate geological data such as lithology and structure, physical property data such as measurements taken on rock samples, and g...
Conference Paper
Full-text available
Joint inversion is a type of inversion carried out for two different physical properties simultaneously. When a single Earth model is derived which fits different, complementary survey data that are sensitive to two physical properties it is more likely to be closer to the true subsurface structure than a single property inversion. A number of synt...
Article
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Earth models used for mineral exploration or other subsurface investigations should be consistent with all available geological and geophysical information. Geophysical inversion provides the means to integrate geological information, geophysical survey data, and physical property measurements taken on rock samples. Incorporation of geological info...
Article
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Throughout the growth of a mineral exploration site, geological ore deposit models are developed based on available data and subsequent interpretations. The accuracy of these models is crucial when used to determine if a deposit is economic. 3D geological Earth models typically comprise wireframe surfaces that represent the geological contacts betw...
Article
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Three-dimensional geological Earth models typically comprise wireframe surfaces of connected triangles that represent geological contacts. In contrast, Earth models used by most current 3D geophysical numerical modeling and inversion methods are built on rectilinear meshes. This is because the mathematics for computing data responses are simpler on...
Article
We develop a method for inverting first-arrival seismic traveltimes without using ray tracing in the forward solution, nor to calculate sensitivity information. We consider unstructured 2-D triangular and 3-D tetrahedral grids for discretizing the subsurface velocity distribution. Unstructured grids provide some computational advantages when dealin...
Article
The Fast Marching Method is an efficient numerical algorithm for propagating interfaces such as first-arrival seismic wave fronts travelling through a velocity distribution. Fast Marching solutions have been developed for use on rectilinear grids in 2-D and 3-D. We are interested in unstructured grids as they provide some computational advantages w...
Article
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Seismic methods continue to receive interest for use in mineral exploration due to the much higher resolution potential of seismic data compared to the techniques traditionally used, namely, gravity, magnetics, resistivity, and electromagnetics. However, the complicated geology often encountered in hard-rock exploration can make data processing and...
Article
Seismic methods have the potential to provide higher resolution than other geophysical techniques. First-arrival traveltimes can be reliably picked from seismic records and can be inverted to obtain distributions of the causative subsurface velocity. We have developed some new methods for forward modelling and inverting first-arrival traveltimes on...
Article
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A single Earth model consistent with multiple geophysical datasets (from different surveys) is more likely to represent the true subsurface than a model consistent with only a single type of data. This is especially true if the surveys sense different aspects of the subsurface and therefore provide complimentary information. For example, surface gr...
Article
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To be reliable, Earth models used for mineral exploration should be consistent with all available geological and geophysical information. During the past several years an important focus of inversion research has been towards advancing the integration of geological data (such as lithology and structure), physical property data (measurements taken o...
Article
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Inversion of magnetic data is complicated by the presence of remanent magnetization. To deal with this problem, we invert magnetic data for a three-component subsurface magnetization vector, as opposed to magnetic susceptibility (a scalar). The magnetization vector can be cast in a Cartesian or spherical framework. In the Cartesian formulation, the...
Article
In this paper, we investigate options for incorporating structural orientation information into under-determined inversions in a deterministic framework (i.e. minimization of an objective function). The first approach involves a rotation of an orthogonal system of smoothness operators, for which there are some important practical details in the imp...
Article
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Application of default, geologically-unconstrained inversions to obtain estimated subsurface physical property models from gravity and aeromagnetic datasets is a common step in many exploration programs. Although the recovered models can help target anomalous features in the subsurface, a reliable model, consistent with all observed geological and...
Article
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Earth models used for mineral exploration should be reliable and consistent with all information available. The current focus of the Geophysical Inversion Facility at the University of British Columbia (UBC-GIF) is towards the development of a new generation of geophysical inversion codes and utilities to advance the integration of geologic and geo...
Article
Geophysical inversion for mineral exploration typically involves a single type of data sensitive to a single physical property. Combining several complimentary types of geophysical data collected over the same Earth region reduces ambiguity and can enhance inversion results. This is important whenever the Earth can not be adequately resolved by any...
Article
We develop an algorithm to invert geophysical magnetic data to recover 3-D distributions of subsurface magnetic susceptibility when the bodies have complicated geometry and possibly high magnetic susceptibility. For the associated forward modelling problem, a full solution to Maxwell's equations for source-free magnetostatics is developed in the di...
Article
Full-text available
Inversion of magnetic data is complicated by the presence of remanent magnetization. To tackle this problem we design a methodology for inverting magnetic data for subsurface magnetization, as opposed to magnetic susceptibility. Our approach contains flexibility to obtain different types of magnetization models and the inversion routine is appropri...
Article
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Previous ecological and paleobiological studies of naticid gastropods have shown that naticids are energy maximizers, choosing prey with the lowest ratio of drilling time cost (determined by prey shell thickness) to energy return benefit (determined by prey internal volume). We tested if naticids select for prey shell thickness by offering two morp...
Article
Summary Magnetic data collected over bodies of high susceptibility contain significant self-demagnetization effects. Examples include mineral exploration surveys over banded iron formations and surveys for detection and discrimination of unexploded ordinance. Standard forward modeling methods that neglect the effects of self-demagnetization can pro...

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