Structural characteristics of a subducting oceanic plate off Western Canada
Notice bibliographique
Résumé
The plate tectonic regime off the southwest coast of British Columbia is convergent; the oceanic Juan de Fuca and Explorer plates are obliquely subducting beneath the continental America plate. To investigate the structural complexity of this region, the Vancouver Island Seismic Project was conducted in August 1980. The principal component of this project was a reversed refraction profile perpendicular to the continental margin, extending 350 km from the America plate to the deep ocean of the Juan de Fuca plate. This work deals with the marine section of the profile. Data from large explosive sources and an airgun were recorded on three ocean bottom seismographs (in the deep ocean, on the continental rise and on the shelf). Continuous seismic reflection profiles complemented the refraction information. To adequately model the seismic structure of this complex region required the application of ray-tracing procedures and a synthetic seismogram technique, based on asymptotic ray theory, for laterally varying media. Consistency between the seismic interpretation and previously published gravity anomaly variations across the margin was verified with the aid of empirical velocity-density relations. Additional seismic constraints were provided by multichannel reflection sections and sonic log data from a nearby well. The aim of all procedures for data modelling was to obtain velocity and density models which had the least structure consistent with all available geophysical information. The interpreted structural section indicates that the sediments thicken from 1 km in the deep ocean to 2 km at the base of the continental rise, where the eastward dip of the oceanic basement increases from 1.4° to about 3° and sediment velocities increase landwards. A stratified upper crustal velocity sequence has been derived below the deep ocean which is similar to that deduced from other studies on the Juan de Fuca plate. This stratification is discordant with the descending oceanic plate further east; it is replaced by a block of relatively low velocity material beneath the continental rise. This unit is interpreted to be a highly sheared and compressed melange. Lower crustal structure remains constant over the entire marine profile, suggesting that the melange material may have been formed as upper crustal layers were scraped off the descending oceanic plate. The lower crust has been modelled as a constant velocity gradient region, extending down to approximately 9 km below sea floor in the deep ocean. At this depth there is a strong decrease in velocity gradient, interpreted to be the Mohorovicic discontinuity. Resolution of Moho structure is poor, but no velocity discontinuity at the boundary is required by the data. There is an increase in the dip of the Moho under the continental rise from about 1° to 6°. The refraction data are thus explicable in terms of a relatively simple, two-dimensional velocity model, which is consistent with multichannel, well-log, and gravity information.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,001 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,002 | 0,003 |
| Études des sciences et des technologies | 0,001 | 0,001 |
| Communication savante | 0,001 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».