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The Mantle Seismic Structure below Canada and Alaska Constrained by a New Absolute P-wavespeed Tomographic Model
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  • Mitch Liddell,
  • Alistair Boyce,
  • Stephen Pugh,
  • Joe Brown,
  • Erin McMurchie,
  • Amber Parsons,
  • Clément Estève,
  • Scott Burdick,
  • Fiona Darbyshire,
  • Sanne Cottaar,
  • Ian Bastow,
  • Andrew Schaeffer,
  • Pascal Audet,
  • Derek Schutt,
  • Richard Aster
Mitch Liddell
University of Quebec at Montreal UQAM

Corresponding Author:[email protected]

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Alistair Boyce
University of Cambridge
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Stephen Pugh
University of Cambridge
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Joe Brown
University of Cambridge
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Erin McMurchie
University of Cambridge
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Amber Parsons
University of Cambridge
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Clément Estève
McGill University
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Scott Burdick
Wayne State University
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Fiona Darbyshire
University of Quebec at Montreal UQAM
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Sanne Cottaar
University of Cambridge
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Ian Bastow
Imperial College London
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Andrew Schaeffer
Sidney Subdivision Natural Resources Canada
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Pascal Audet
University of Ottawa
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Derek Schutt
Colorado State University
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Richard Aster
Colorado State University
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Abstract

Mapping absolute P-wavespeeds in the Canadian and Alaskan mantle will further our understanding of its present-day state and evolution. S-wavespeeds are relatively well constrained, especially across Canada, but are primarily sensitive to temperature while complimentary P-wavespeed constraints provide better sensitivity to compositional variations. One technical issue concerns the difficulties in extracting absolute arrival-time measurements from often-noisy data recorded by temporary seismograph networks. Such processing is required to ensure that regional Canadian datasets are compatible with supplementary continental and global datasets provided by global pick databases. To address this, we utilize the Absolute Arrival-time Recovery Method (Boyce et al., 2017). We extract over 180,000 new absolute arrival-time residuals from seismograph stations across Canada and Alaska that include both land and ocean bottom seismometers. We combine these data with the latest USArray P-wave arrival-time data from the contiguous US and Alaska. Using an adaptively parameterised least-squares tomographic inversion we develop a new absolute P-wavespeed model, with focus on Canada and Alaska (CAP21). Initial results suggest fast wavespeeds characterise the upper mantle beneath eastern and northern Canada. A sharp transition between the slow wavespeeds below the North American Cordillera and the fast wavespeeds of the stable continental interior appears to follow the Cordilleran Deformation Front (CDF) in southwest Canada. Slow wavespeeds below the Mackenzie Mountains may extend further inland of the CDF in northwest Canada. In Alaska, CAP21 illuminates both lithospheric structure and the along strike morphology of the subducting slab. The newly compiled data may also improve resolution of subducted slab remnants in the mid-mantle below the North American continent, crucial to help constrain the formation of the Alaskan peninsular at ≥50Ma.