Seismicity along the continental margin of Vancouver Island
Notice bibliographique
Résumé
The oceanic Juan de Fuca and Explorer plates are subducting beneath the continental North America plate west of Vancouver Island at rates of 47 mm/yr and 21 mm/yr, respectively. The Nootka fault zone, which is the boundary between the two subducting plates, experiences left-lateral shear due to their different rate of subduction. The Juan de Fuca/North America interaction vector is normal to the boundary beneath central-south Vancouver Island and oblique beneath western Washington. During the last 15 years, seismograph station coverage in western Canada has been adequate to record a good number of small magnitude earthquakes lying mainly in three regions: the Nootka fault zone, the Georgia Strait-Puget Sound region, and along the west coast of Vancouver Island and immediate offshore region. A detailed study of seismicity data in the Vancouver Island and offshore region, within the depth range of 25-55 km and recorded in the Canadian Earthquake Catalogue during the period 1976-1989, has been undertaken. The objectives of this study are to determine the frequency of occurrence and b-value, to improve the hypocentral locations and to interpret them in terms of both structure and the subductions process, and to examine the focal mechanisms to gain understanding of the stress field. A total of 127 earthquakes satisfied the depth range criteria and were analyzed in detail. Earthquake depths, recalculated with a recently determined velocity structure from refraction-reflection data and using the best station distribution and the more reliable arrival times, delineate a zone of seismicity beneath central-south Vancouver Island. The hypocenters show a distinct band of activity which extends ~60 km down-dip at a distance range of 35 to 95 km from the shelf edge and at a depth of 25 to 45 km. The structure is about 9 km thick and dips at an angle of 14° at N29°E. Most of these deep earthquakes are located in the subducting oceanic crust, a conclusion consistent with the position of the oceanic plate from other geophysical studies. The b-value of the magnitude-frequency distribution calculated as 0.79 also is consistent with the conclusion of the seismicity occurring within the slab, on the basis of similar studies in western Washington and in other subduction zones. Areally, the new results confirm previous suggestions that the subducting plate is arched below the Georgia Strait-Puget Sound region. Composite focal mechanism solutions constructed for five groups of earthquakes show strike-slip and normal faulting mechanisms, but no thrust events. This important result confirms, at the small magnitude level, previous observations of the absence of thrust faulting earthquakes. Normal faulting may be associated with plate bending, an expected result, but the strike-slip mechanisms which suggest lateral shearing within the subducting plate, are an unexpected result. The composite of P (pressure) and T (tension) axes does not show a preferred orientation; the only noticeable feature is that the T axes indicate in-plane tensions. The diversity in the orientation of the P and T axes suggests a more complex state of stresses in the subducted slab than expected from the application of a normal subduction model. Such a complexity may be related to the arched plate geometry, to stresses generated by phase changes in the plate and to plate interactions at their boundaries.
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 distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,001 | 0,000 |
| Communication savante | 0,000 | 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) | 0,008 | 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 tête enseignante, 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 ».