Velocity structure of the subducted Yakutat Terrane, Alaska: Insights from guided waves
Dispersed P wave arrivals from intermediate-depth earthquakes in the Alaskan subduction zone provide insight into the low-velocity structure of the subducting oceanic crust. P wave arrivals from 41 earthquakes in the eastern section of the arc show significant guided wave dispersion, with high-frequ...
| Main Authors: | , , |
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| Format: | Journal article |
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American Geophysical Union
2018
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| Summary: | Dispersed P wave arrivals from intermediate-depth earthquakes in the Alaskan subduction zone provide insight into the low-velocity structure of the subducting oceanic crust. P wave arrivals from 41 earthquakes in the eastern section of the arc show significant guided wave dispersion, with high-frequency ( > 1 Hz) energy delayed by up to 2-3 s. We simulate this dispersion using a 2-D finite difference waveform propagation model, systematically varying both P wave velocity and low-velocity layer thickness parameters to find the lowest misfit between the observed and synthetic waveforms. We infer a 6 to 10 km thick low-velocity layer with a P wave velocity contrast of 7-15% with the overriding mantle, velocities which cannot be entirely accounted for by metamorphosed mid-ocean ridge basalt compositions. We postulate that this structure is the remnant of the subducted Yakutat terrane, significantly thinned at depth by metamorphism or delamination of material during subduction. |
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