Magnitude conversion relations for very short distances: The Charlevoix, Quebec, Seismic Zone
Bibliographic record
Abstract
The Nuttli (MN) scale is the most commonly used magnitude scale in eastern Canada. It is based on the amplitude of the Lg phase and therefore is not appropriate for distances of less than 50 km where the Lg phase is not developed. The original Richter, ML, scale developed for use in California and known to be inappropriate for eastern North America, is used only when the Lg phase is non-existent or highly attenuated, generally for earthquakes recorded at distances of less than 50 km or earthquakes occurring in oceanic crust. In the Charlevoix, Quebec, Seismic Zone the station density is such that it is possible to routinely locate earthquakes of magnitude 1.0 or smaller. Magnitudes for these smallest earthquakes are usually ML. For many slightly larger earthquakes, the MN values are based on readings at a single station, most often DAQ, as the earthquakes are usually not well-recorded at greater distances. Establishing a magnitude relation between MN calculated at appropriate distances and MN or ML calculated at close distances would enable more magnitude readings to be used for the small earthquakes and a magnitude recurrence relation to be established over a wider magnitude range. Using data from earthquakes occurring within the Charlevoix Seismic Zone for which MN was reported as the preferred magnitude we calculated ML and MN from stations at less than 50 km from the epicenter and compared them to the published or event magnitudes. ML underestimates the magnitude by about 1 magnitude unit whereas the MN (close) values were only about 0.2 units smaller than the presumed magnitude. These results suggest that MN would be a better measure of the earthquake size even when calculated out of range and not from an Lg wave. We also evaluated the effect of using hypocentral distance instead of epicentral distance for earthquakes at less than 50 km but found that the difference was not significant in most cases. An evaluation of DAQ single station versus multi-station magnitudes suggests that DAQ station MN magnitudes may overestimate the size of the earthquake by about 0.2 magnitude units.
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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 | 0.003 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.003 | 0.004 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.014 | 0.002 |
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".