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Plateau subduction, intraslab seismicity, and the Denali (Alaska) volcanic gap Chuang, Yuling (Lindsay)
Abstract
Tectonic tremors in Alaska (USA) are associated with subduction of the Yakutat plateau, but their origins are unclear due to lack of depth constraints. We have processed tremor recordings to extract low-frequency earthquakes (LFEs), and generated a set of six LFE waveform templates via iterative network matched filtering and stacking. The timing of impulsive P (compressional) wave and S (shear) wave arrivals on template waveforms places LFEs at 40–58 km depth, near the upper envelope of intraslab seismicity and immediately updip of increased levels of intraslab seismicity. S waves at near-epicentral distances display polarities consistent with shear slip on the plate boundary. We compare characteristics of LFEs, seismicity, and tectonic structures in central Alaska with those in warm subduction zones, and propose a new model for the region’s unusual intraslab seismicity and the enigmatic Denali volcanic gap (i.e., an area of no volcanism where expected). We argue that fluids in the Yakutat plate are confined to its upper crust, and that shallow subduction leads to hydromechanical conditions at the slab interface in central Alaska akin to those in warm subduction zones where similar LFEs and tremor occur. These conditions lead to fluid expulsion at shallow depths, explaining strike-parallel alignment of tremor occurrence with the Denali volcanic gap. Moreover, the lack of double seismic zone and restriction of deep intraslab seismicity to a persistent low-velocity zone are simple consequences of anhydrous conditions prevailing in the lower crust and upper mantle of the Yakutat plate.
Item Metadata
Title |
Plateau subduction, intraslab seismicity, and the Denali (Alaska) volcanic gap
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
2018
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Description |
Tectonic tremors in Alaska (USA) are associated with subduction of the Yakutat
plateau, but their origins are unclear due to lack of depth constraints. We have
processed tremor recordings to extract low-frequency earthquakes (LFEs), and
generated a set of six LFE waveform templates via iterative network matched filtering
and stacking. The timing of impulsive P (compressional) wave and S (shear) wave
arrivals on template waveforms places LFEs at 40–58 km depth, near the upper
envelope of intraslab seismicity and immediately updip of increased levels of
intraslab seismicity. S waves at near-epicentral distances display polarities consistent
with shear slip on the plate boundary. We compare characteristics of LFEs, seismicity,
and tectonic structures in central Alaska with those in warm subduction zones, and
propose a new model for the region’s unusual intraslab seismicity and the enigmatic
Denali volcanic gap (i.e., an area of no volcanism where expected). We argue that
fluids in the Yakutat plate are confined to its upper crust, and that shallow subduction
leads to hydromechanical conditions at the slab interface in central Alaska akin to
those in warm subduction zones where similar LFEs and tremor occur. These
conditions lead to fluid expulsion at shallow depths, explaining strike-parallel
alignment of tremor occurrence with the Denali volcanic gap. Moreover, the lack of
double seismic zone and restriction of deep intraslab seismicity to a persistent
low-velocity zone are simple consequences of anhydrous conditions prevailing in the
lower crust and upper mantle of the Yakutat plate.
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Genre | |
Type | |
Language |
eng
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Date Available |
2018-01-19
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Provider |
Vancouver : University of British Columbia Library
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Rights |
Attribution-NonCommercial-NoDerivatives 4.0 International
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DOI |
10.14288/1.0363105
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
2018-02
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Campus | |
Scholarly Level |
Graduate
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Rights URI | |
Aggregated Source Repository |
DSpace
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Rights
Attribution-NonCommercial-NoDerivatives 4.0 International