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Unravelling a 2300 year long sedimentary record of megathrust and intraslab earthquakes in proglacial Skilak Lake, south-central Alaska

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Abstract
Seismic hazards in subduction settings typically arise from megathrust, intraslab and crustal earthquake sources. Despite the frequent occurrence of intraslab earthquakes in subduction zones and their potential threat to communities, their long-term recurrence behaviour is barely studied. Sedimentary sequences in lakes may register ground shaking from different seismic sources. This study investigates two long sediment cores (13 m and 16 m) from Skilak Lake, a proglacial lake in south-central Alaska, to evaluate whether different seismic sources leave a distinct imprint. The sedimentary record shows a continuously varved sediment sequence, occasionally interrupted by turbidites, slump deposits and tephra beds. Turbidites and slump deposits were objectively identified using a statistical outlier analysis on varve thickness. The earthquake origin of these deposits was ascertained by resemblance with deposits induced by instrumentally recorded earthquakes (for example, 1964 ce M-w 9.2 megathrust and 1954 ce M-w 6.4 intraslab earthquakes) and correlation with multiple coeval landslide deposits on sub-bottom profiles. The Skilak Lake record chronicles 19 earthquakes with moderate to very high confidence level in the past 1350 years. The sedimentary evidence of instrumentally-recorded intraslab and megathrust earthquakes within the past 70 years demonstrates that not only megathrust earthquakes, but also past intraslab events are recorded. Although reported seismic intensities at Skilak Lake are comparable for the 1964 ce megathrust and the 1954 ce intraslab earthquakes, the long duration and low frequency content of seismic ground motion during megathrust earthquakes facilitate the triggering of multiple, voluminous landslides and the generation of megaturbidites. In contrast, the shorter duration and higher frequency source spectrum of intraslab earthquakes may only induce surficial slope remobilization and the generation of thinner turbidites. This study demonstrates that the sedimentary record of Skilak Lake has the potential to decipher multiple seismic sources, which opens possibilities for a comprehensive seismic hazard analysis for south-central Alaska.
Keywords
UPPER COOK INLET, HISTORIC EARTHQUAKES, LACUSTRINE SEDIMENTS, VARVE, CHRONOLOGY, REDOUBT VOLCANO, KENAI PENINSULA, EKLUTNA LAKE, TEPHROCHRONOLOGY, DEPOSITS, TSUNAMI, Earthquake, proglacial lakes, south-central Alaska, subaqueous, landslides, tephra, turbidites

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MLA
Praet, Nore, et al. “Unravelling a 2300 Year Long Sedimentary Record of Megathrust and Intraslab Earthquakes in Proglacial Skilak Lake, South-Central Alaska.” SEDIMENTOLOGY, 2022, doi:10.1111/sed.12986.
APA
Praet, N., Van Daele, M., Moernaut, J., Mestdagh, T., Vandorpe, T., Jensen, B. J. L., … De Batist, M. (2022). Unravelling a 2300 year long sedimentary record of megathrust and intraslab earthquakes in proglacial Skilak Lake, south-central Alaska. SEDIMENTOLOGY. https://doi.org/10.1111/sed.12986
Chicago author-date
Praet, Nore, Maarten Van Daele, Jasper Moernaut, Thomas Mestdagh, Thomas Vandorpe, Britta J. L. Jensen, Robert C. Witter, Peter J. Haeussler, and Marc De Batist. 2022. “Unravelling a 2300 Year Long Sedimentary Record of Megathrust and Intraslab Earthquakes in Proglacial Skilak Lake, South-Central Alaska.” SEDIMENTOLOGY. https://doi.org/10.1111/sed.12986.
Chicago author-date (all authors)
Praet, Nore, Maarten Van Daele, Jasper Moernaut, Thomas Mestdagh, Thomas Vandorpe, Britta J. L. Jensen, Robert C. Witter, Peter J. Haeussler, and Marc De Batist. 2022. “Unravelling a 2300 Year Long Sedimentary Record of Megathrust and Intraslab Earthquakes in Proglacial Skilak Lake, South-Central Alaska.” SEDIMENTOLOGY. doi:10.1111/sed.12986.
Vancouver
1.
Praet N, Van Daele M, Moernaut J, Mestdagh T, Vandorpe T, Jensen BJL, et al. Unravelling a 2300 year long sedimentary record of megathrust and intraslab earthquakes in proglacial Skilak Lake, south-central Alaska. SEDIMENTOLOGY. 2022;
IEEE
[1]
N. Praet et al., “Unravelling a 2300 year long sedimentary record of megathrust and intraslab earthquakes in proglacial Skilak Lake, south-central Alaska,” SEDIMENTOLOGY, 2022.
@article{8756916,
  abstract     = {{Seismic hazards in subduction settings typically arise from megathrust, intraslab and crustal earthquake sources. Despite the frequent occurrence of intraslab earthquakes in subduction zones and their potential threat to communities, their long-term recurrence behaviour is barely studied. Sedimentary sequences in lakes may register ground shaking from different seismic sources. This study investigates two long sediment cores (13 m and 16 m) from Skilak Lake, a proglacial lake in south-central Alaska, to evaluate whether different seismic sources leave a distinct imprint. The sedimentary record shows a continuously varved sediment sequence, occasionally interrupted by turbidites, slump deposits and tephra beds. Turbidites and slump deposits were objectively identified using a statistical outlier analysis on varve thickness. The earthquake origin of these deposits was ascertained by resemblance with deposits induced by instrumentally recorded earthquakes (for example, 1964 ce M-w 9.2 megathrust and 1954 ce M-w 6.4 intraslab earthquakes) and correlation with multiple coeval landslide deposits on sub-bottom profiles. The Skilak Lake record chronicles 19 earthquakes with moderate to very high confidence level in the past 1350 years. The sedimentary evidence of instrumentally-recorded intraslab and megathrust earthquakes within the past 70 years demonstrates that not only megathrust earthquakes, but also past intraslab events are recorded. Although reported seismic intensities at Skilak Lake are comparable for the 1964 ce megathrust and the 1954 ce intraslab earthquakes, the long duration and low frequency content of seismic ground motion during megathrust earthquakes facilitate the triggering of multiple, voluminous landslides and the generation of megaturbidites. In contrast, the shorter duration and higher frequency source spectrum of intraslab earthquakes may only induce surficial slope remobilization and the generation of thinner turbidites. This study demonstrates that the sedimentary record of Skilak Lake has the potential to decipher multiple seismic sources, which opens possibilities for a comprehensive seismic hazard analysis for south-central Alaska.}},
  author       = {{Praet, Nore and Van Daele, Maarten and Moernaut, Jasper and Mestdagh, Thomas and Vandorpe, Thomas and Jensen, Britta J. L. and Witter, Robert C. and Haeussler, Peter J. and De Batist, Marc}},
  issn         = {{0037-0746}},
  journal      = {{SEDIMENTOLOGY}},
  keywords     = {{UPPER COOK INLET,HISTORIC EARTHQUAKES,LACUSTRINE SEDIMENTS,VARVE,CHRONOLOGY,REDOUBT VOLCANO,KENAI PENINSULA,EKLUTNA LAKE,TEPHROCHRONOLOGY,DEPOSITS,TSUNAMI,Earthquake,proglacial lakes,south-central Alaska,subaqueous,landslides,tephra,turbidites}},
  language     = {{eng}},
  pages        = {{30}},
  title        = {{Unravelling a 2300 year long sedimentary record of megathrust and intraslab earthquakes in proglacial Skilak Lake, south-central Alaska}},
  url          = {{http://dx.doi.org/10.1111/sed.12986}},
  year         = {{2022}},
}

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