Subduction Zone Interface Structure within the Southern MW9.2 1964 Great
Alaska Earthquake Asperity: Constraints from Receiver Functions Across a
Spatially Dense Node Array
Abstract
We conduct a high-resolution teleseismic receiver function investigation
of the subducting plate interface within the Alaskan forearc beneath
Kodiak Island using data collected as part of the Alaska Amphibious
Community Seismic Experiment in 2019. The Kodiak node array consisted of
398 nodal geophones deployed at ~200 m spacing on
northeastern Kodiak Island within the southern asperity of the 1964
MW9.2 Great Alaska earthquake. Receiver function images
at frequencies of 1.2 and 2.4 Hz show a coherent, slightly dipping
velocity increase at ~30-40 km depth consistent with the
expected slab Moho. In contrast to studies within the northern asperity
of the 1964 rupture, we find no evidence for a prominent low-velocity
layer above the slab Moho thick enough to be resolved by upgoing P-to-S
conversions. These results support evidence from seismicity and geodetic
strain suggesting that the 1964 rupture connected northern (Kenai) and
southern (Kodiak) asperities with different plate interface properties.