Point-source inversion neglecting a nearby free surface: simulation of the Underground Research Laboratory, Canada
Notice bibliographique
Résumé
The aim of this study was to investigate the effects of the inconsistency between the model used and the actual structure on the inversion of point-source parameters. Specifically, we studied the effects of ignoring a reflecting interface in the model. Such a situation frequently occurs when events with sources close to mine excavations are recorded and subsequently processed using a simplified model describing the interface only approximately or ignoring it completely. In this case, it is important to ask how reliable the retrieved mechanism is. An inversion algorithm with indirect parametrization of the source (INPAR) was applied. A numerical study was performed, in which the mechanism and source time function of a point source were sought in a model inconsistent with the actual structure. The ray synthetic wavefield generated by a source situated close to a free surface of a homogeneous half-space was treated as the observed data. The free surface was then ignored when constructing the Green's function necessary for the point-source inversion. Thus, the inconsistent response of the medium including only direct phases was used to invert the observed seismograms, which contain both direct and reflected phases. The configuration of the Underground Research Laboratory (URL) of the Atomic Energy Canada Ltd. was simulated in the synthetic experiments. 16 triaxial sensors were situated around the underground tunnel, the face of which was taken to represent the free surface near the hypocentre. High-frequency seismograms were synthetized with a frequency of around 10 kHz. This is close to the prevailing frequency of the actual URL records. It was found that gross features of the source such as orientation of the double couple and the general features of the source time function can be retrieved satisfactorily when the hypocentre is localized correctly. Formal error analysis, however, yields rather large error estimates due to the omission of the free surface, providing us with acceptably constrained solutions at about 70 per cent confidence level only. Mislocation of the hypocentre of the order of seven to 14 wavelengths and/or contamination of the data by noise with an amplitude amounting to 20 per cent of the data amplitude both distort retrieved source parameters and make them rather uncertain. The retrieved orientation deviates by more than 20° and its 70 per cent confidence region extends several tens of degrees. As a consequence of the mismodelling of the medium represented by the neglect of the free surface, spurious non-double couple (DC) components appear in the mechanism. Two URL events from 1991 September 25 separated by 4 s were processed, and a large majority of the compensated linear-vector dipole (CLVD) was found there. The CLVD along the P-axis at the earlier event was replaced by the CLVD along the T-axis at the following one, which suggests an over-relaxation of the stress during the first event and its partial restoration by the subsequent event.
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 | 0,001 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,001 | 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 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 ».