Velocity structure of the subducted Yakutat Terrane, Alaska: Insights from guided waves

• Published in: Geophysical Research Letters
• Main Authors: Coulson, S, Garth, T, Rietbrock, A
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: American Geophysical Union 2018
• Subjects: Yakutat; Alaska
• Online Access: https://doi.org/10.1002/2017GL076583; https://ora.ox.ac.uk/objects/uuid:a04cbd57-a5ae-46be-9325-517f1582ea81

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.