The Børglum fault, Sorgenfrei-Tornquist Zone, northern Denmark: a natural laboratory to investigate a hidden active intra-plate fault
Bibliographic record
Abstract
Intra-plate faults are a special challenge in seismology, because of the long intervals between individual seismic events and the fact that such faults are often hidden below young sediments. This makes such faults difficult to detect and thus they can be the source of unexpected and fatal earthquakes. The Børglum fault is located in a slowly deforming area in northern Denmark and represents one of the northern boundary faults of the Sorgenfrei-Tornquist Zone. With a length of at least 250 km, it is capable to produce significant seismic events. Previous studies indicated that the Børglum fault is seismically active and this fuelled the demand for further analysis of the fault structure and its seismic hazard potential. Due to excellent coastal outcrops and available high-resolution DEMs, the Børglum fault is a perfect natural laboratory to analyse a hidden active fault. We present a multi-method approach based on outcrop analyses, shear-wave seismic reflection surveys, DEM analysis and numerical simulations of deglaciation-induced Coulomb failure stress change. The 2D seismic surveys show that the analysed segment of the Børglum fault is a complex fault system with a strike-slip component. This interpretation is based on positive flower structures on the seismic surveys, the presence of elongated mini-basins and the geometry of the drainage pattern in the study area. On the basis of soft-sediment deformation structures and disaggregation bands developed in Late Pleniglacial to Lateglacial marine and lacustrine deposits, we derive repeated phases of fault activity with earthquake magnitudes of up to M=7. The geometry of the drainage pattern in the study area indicates a close relationship between fault activity and topography. Based on the timing of fault activity and results from numerical simulations of deglaciation-related lithospheric stress build-up, it is likely that the Børglum fault is a glacially triggered fault and that the analysed part of the Sorgenfrei-Tornquist Zone is susceptible to glacially triggered fault reactivation.
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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 | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".