6 Conclusions
We analyzed teleseismic P waves from 398 autonomous three-component 5-Hz
nodal geophones on Kodiak Island as part of the Alaska Amphibious
Community Seismic Experiment. We calculated RFs with a Gaussian value of
2.5 (~1.2 Hz) and a Gaussian value of 5.0
(~2.4 Hz). The lower frequency (1.2 Hz) RFs were
comparable to RFs from near-collocated broadband seismometers, and the
higher frequency (2.4 Hz) RFs image produced more details. In both low
and high frequency images, there is a coherent, SE to NW dipping
positive phase at the expected slab Moho depth but no observable
negative arrival to indicate phase conversions at the oceanic crust. To
help explain the observed RFs, we calculated synthetic RFs from 1-D
models. These synthetic tests suggest that the overriding forearc
material and Pacific oceanic crust have nearly identical seismic
velocities and densities. We conclude that the 1964 Great Alaska
Earthquake ruptured beyond the extent of the low-velocity shear zone
observed in the Kenai asperity into a structural setting beneath Kodiak
Island with little seismic contrast across the plate boundary interface.