Three-dimensional finite-volume time-domain modeling of graphitic fault zones in the Athabasca Basin using unstructured grids.
Bibliographic record
Abstract
In this thesis, numerical modeling methods for geophysical time-domain electromag- netic (EM) problems and their applications in modeling graphitic faults in the Atha- basca Basin are investigated. A finite-volume time-domain numerical modeling method is developed. The method uses unstructured Delaunay-Voronoï dual meshes. Such unstructured meshes are more flexible and efficient when models containing geological units with complex geometries and topography need to be considered. A model build- ing procedure is established to construct arbitrarily complex models with topography. The procedure locally refines the mesh quality at certain areas such as loop sources and receivers in order to obtain better numerical results. For modeling time-domain EM problems, two approaches are used: the electric field approach and the potential approach. The electric field method directly solves the electric field Helmholtz equation while the potential method solves the Helmholtz equation expressed using vector and scalar potentials. The electric field method is simpler in theory and results in a smaller linear system of equations compared to potential methods. The potential method, on the other hand, is more complex intheory and a larger linear system of equations needs to be solved. However, using the potentials method enables the decomposition of the electric field into galvanic and inductive parts, which is helpful for understanding the physics behind the behaviour of the EM fields in the ground. In addition, the linear system of equations is better conditioned which potentially allows the use of iterative methods to solve it. Both methods are validated by comparing the modeling results with analytic solu- tions for homogeneous half-space models and numerical results for models presented in the literature. The modeling methods developed in this thesis are then applied to the modeling of real EM data collected in the Athabasca Basin. Thin, steeply dip- ping graphitic fault systems, which are linked to the formation of uranium deposits are present in the basin and have a large conductivity contrast with the background host. Because of the close relationship between the graphitic faults and the uranium deposits, time-domain EM surveys are important tools for uranium exploration in the basin. Geological models of the graphitic fault systems are discretized with unstruc- tured grids using the model building procedure developed in this thesis. Two real data sets that were previously collected from the Athabasca Basin are modeled and the modeling results are compared with the real data. The match between the calculated three-component responses and real data is good for models built based on geological information, drilling information, and trial-and-error. These models can help us to infer the complex geometry and conductivity features of the subsurface conductor be- yond the areas targeted by drilling. Therefore, 3D modeling of realistic, complicated real-life conductive targets such as in the uranium exploration in the Athabasca Basin or any other classic mineral exploration for a conductive target with complex shape is an important tool.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".