The seismogenic zones of an M2.0-5.5 earthquakes successfully recovered in deep South African gold mines: the outcomes and the follow-up plan
Notice bibliographique
Résumé
<p>This paper reports on the outcomes of the ICDP drilling into seismogenic zones of M2.0-5.5 earthquakes in South African (SA) gold mines (DSeis; 2017-2018), the follow-up work in 2019, and planned post-drilling activity from 2020 onwards.</p><p>In deep SA gold mines, seismogenic zones evolve ahead of thin tabular excavations. Normal faulting prevails because mining enhances the vertical maximum principal stress. At 1km depth at the Cooke 4 mine, we elucidated the evolution of the seismogenic zone with a dense acoustic emission network. In 2017, we successfully recovered both the metasedimentary host rock (mainly quartzite ~2.8 Ga) and samples of the seismogenic zone with well-preserved fracture systems using a triple-tube (BQ 1.5m-long). Subsequent laboratory work investigated critical characteristics of rock-rock friction.</p><p>In 2014, an M5.5 earthquake, the largest in deep South African gold mining districts, took place. Dense seismic networks, both on the Earth’s surface and at 2-3 km depth, showed that this event was atypical because it was a sinistral event on an unknown geological structure below the mining horizon in West Rand Group strata (~2.9 Ga). Inversion and back-projection of the ground motion showed complicated but unilateral rupture propagation. The densest population of aftershocks shows a sharp upper cut-off and streaks, both dipping to the south.  Its centroid lies outside the significant main rupture zone. In 2017, we commenced drilling at a site at 2.9km depth in a tension quadrant of the sinistral faulting, several hundreds of meters above the upper fringe of the M5.5 aftershock plane. During 2017-2018, we drilled holes, of a total length of 1.6 km. With a 1.5m NQ triple-tube for the critical section, we could recover the fault materials and the host rock with the seismic fracture system well preserved. Borehole logging and core curation in SA and laboratory work at international organizations, including Kochi Core Center Japan (KCC), followed during 2017-2019. With the geology data mapped on the mining horizons and the legacy seismic reflection data as additional information, the following picture is emerging: (a) transition of the stress regime from normal-faulting to sinistral-faulting; (b) stress localization; (c) heterogeneity in the aftershock distribution as well as the segregation between the main rupture and aftershocks, potentially correlated with significant heterogeneity in mechanical properties; (d) a role of an altered lamprophyre dike; (e) hypersaline brine with salinity even higher than measurements at other deep gold mines, potentially as old as brine found at Kidd Creek mine, Canada; and (f) abiogenic gas and organic carbon.</p><p>These data sets allow us to address questions in earthquake and deep-life sciences raised in the ICDP Science Plan (2014-2019). In 2019, the ICDP Executive Committee described DSeis as a ‘successful’ project. To integrate and discuss the outcomes in greater depth and plan additional follow-up work, we are planning a post-drilling workshop in November 2020 or January 2021 at KCC before we return the imported critical section of the core to South Africa.</p>
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 | 0,000 | 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) | 0,000 | 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 ».