| Titre | Lithospheric strength and stress revisited: pruning the Christmas tree |
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| Auteur | Ellis, S; Wang, K |
| Source | Earth and Planetary Science Letters vol. 595, 117771, 2022 p. 1-13, https://doi.org/10.1016/j.epsl.2022.117771 |
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| Année | 2022 |
| Séries alt. | Ressources naturelles Canada, Contribution externe 20220167 |
| Éditeur | Elsevier |
| Document | publication en série |
| Lang. | anglais |
| DOI | https://doi.org/10.1016/j.epsl.2022.117771 |
| Media | papier; numérique; en ligne |
| Formats | pdf |
| Sujets | lithosphère; détermination des contraintes; craton; frontières de plaques; milieux tectoniques; tectonique; Sciences et technologie |
| Illustrations | modèles; graphiques; coupes lithologiques; tableaux |
| Programme | Géoscience pour la sécurité publique Risques géologique du tremblement de terre |
| Diffusé | 2022 08 07 |
| Résumé | (non publié)
Whether lithospheric stress can reach the maximum level predicted by the Christmas-tree strength envelope is a fundamental question but with controversial answers. There is little
controversy that a deforming lithosphere in high heat flow regions is likely critically stressed, i.e., at full yield at all depths, as described by the envelope. But different conceptual frameworks offer opposite views for very cold lithosphere,
either at full yield or far below yield. Here, we use simple numerical models to investigate stresses in end-member cold cratonic lithosphere (e.g., Canadian Craton) in comparison with end-member warm plate-boundary lithosphere (e.g., Canadian
Cordillera). The two key elements of our modelling are (1) that lithospheric stress builds up elastically with horizontal tectonic loading not only in the elastic-frictional brittle regime but also in the viscoelastic ductile regime, and (2) that the
stress level is limited by the available tectonic force. In a cratonic lithosphere, the limiting tectonic force is sustained by competent rock material over a large depth range, represented by the competent thickness Tc that exceeds 90 km. The
lithosphere undergoes mostly elastic deformation at a stress level of a few tens of MPa. While weakly stressed strong lithosphere can still produce limited earthquakes at shallow depths due to structural and stress heterogeneity, the lithospheric
stress under horizontal tectonic loading is theoretically predicted to be orders of magnitude lower than predicted by the Christmas-tree envelope. Stresses in a real lithosphere may substantially deviate from this theoretical level because of
spatiotemporal variations in rheology and structure. For example, the stress memory of past loading history in cold lithosphere may or may not be erased by more recent tectonic loadingstresses. Because much of previous scientific debates on
lithospheric stress levels and comparison with seismicity were focused on topographically induced flexural stress, we also investigate the effect of vertical loading. We show that the effective elastic thicknesses Te derived from the flexural
response is a reasonable proxy for Tc derived from horizontal tectonic loading; a very large Te such as > 80 km is generally associated with very low tectonic stress far below yield. However, the flexure-induced bending stress is not directly
comparable with seismicity because it may either enhance or suppress seismogenic stress in the crust. |
| Sommaire | (Résumé en langage clair et simple, non publié)
Une question fondamentale, mais extrêmement controversée pour comprendre les processus et les risques de séismes intraplaques, est le degré de
contrainte tectonique qui provoque les séismes. Selon l'opinion la plus répandue, la contrainte doit être suffisamment élevée partout pour que la croûte soit toujours au bord de la rupture sismique, c. à d. prête à produire des séismes lors de
petites perturbations. Dans la présente étude théorique, nous faisons la preuve que dans les anciennes régions cratoniques, comme dans une grande partie de l'est du Canada, la contrainte est très faible et la croûte est généralement loin de la
rupture. L'occurrence de séismes dans le cas d'une très faible contrainte tectonique de fond reflète une hétérogénéité structurelle avec soit une contrainte localement élevée, soit des failles localement faibles. Ces résultats constituent un cadre
conceptuel pour l'étude des séismes naturels et induits dans les plaques tectoniques. |
| GEOSCAN ID | 330336 |
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