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Sédimentation gravitaire et paléosismicité d'une marge active : Exemple de la marge en subduction Hikurangi en Nouvelle-Zélande

Abstract : Earthquakes are known to trigger gravity flows and turbidites along continental margins. These deposits provide meaningful tools to establish long-term paleo-earthquake records. The detailed analysis of a series of sediment cores, collected strategically in three distinct sedimentary basins along the Hikurangi subduction margin of New Zealand, allows the characterisation of gravity flow sedimentation since 18,000 years, as well as the identification of the controlling parameters and the triggering mechanisms of turbidites. The sedimentary record is comprised of alternating lithofacies and depositional modes, namely hemipelagite (marine sedimentation), turbidites (turbidity currents), debrites (debris flows), and tephra (ash fall), which are controlled by margin morphology and glacio-eustatic fluctuations. Floods, volcanic eruptions and slope failures are the three triggering mechanisms of turbidites along the margin. More than 90% of them are triggered by slope failures from the upper slope (150-1,200 m deep) consecutively to earthquakes. The adaptation of empirical relationships to evaluate slope stability suggests that these turbidites are the sedimentary record of repetitive ruptures of three active faults, including the plate interface, and correspond to Mw≥7.3 earthquakes occurring with a return time of 150±50 years. Amongst theses turbidites, 20 show a synchronicity of trigger across the entire margin and are more voluminous. They correspond to ruptures on the plate interface, which generate Mw7.5-8.4 earthquakes. Return times show a clustering of interface earthquakes with alternating active periods of low return time (305-610 years) and quiescence periods of high return time (1480-2650 years). Integrated to ongoing simulations, this earthquake calendar would provide new constraints to ascertain the seismic hazard.
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Submitted on : Wednesday, November 21, 2012 - 1:16:23 PM
Last modification on : Thursday, June 2, 2022 - 2:48:11 PM
Long-term archiving on: : Friday, February 22, 2013 - 3:48:27 AM

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  • HAL Id : tel-00755471, version 1

Citation

Hugo Pouderoux. Sédimentation gravitaire et paléosismicité d'une marge active : Exemple de la marge en subduction Hikurangi en Nouvelle-Zélande. Stratigraphie. Université Rennes 1, 2011. Français. ⟨NNT : ⟩. ⟨tel-00755471⟩

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