Enhanced Resolution of the Subducting Plate Interface in Central Alaska From Autocorrelation of Local Earthquake Coda

Subducting plates below 10-km depth are primarily imaged using phases from teleseismic earthquakes at frequencies dominantly below 1Hz, resulting in low-resolution images compared to fault zone thickness. Here we image the plate boundary zone in Alaska using scattered body wave arrivals in local earthquake coda to produce a higher-resolution image of the slab. An autocorrelation method successfully extracts coherent arrivals from the local earthquake signals. Our autocorrelation results image interfaces associated with the subducting oceanic plate at higher resolution than our teleseismic receiver functions, with increased coherence and sharper boundaries. Our results provide one of the first coherent structural images of the seismogenic zone using scattered local body waves. Amplitudes suggest that seismic wave speed decreases with increasing depth within the low-velocity zone, supporting lithologic rather than purely overpressure models for the zone in our region. Similar methodologies using dense stations could provide higher-resolution images to characterize crustal and uppermost mantle boundaries globally.