Plateau subduction, intraslab seismicity, and the Denali (Alaska) volcanic gap

Geology
By: , and 

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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.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Plateau subduction, intraslab seismicity, and the Denali (Alaska) volcanic gap
Series title Geology
DOI 10.1130/G38867.1
Volume 45
Issue 7
Year Published 2018
Language English
Publisher Geological Society of America
Contributing office(s) Volcano Science Center
Description 4 p.
First page 647
Last page 650
Country United States
State Alaska
Other Geospatial Denali volcanic gap