Subduction Zone Interface Structure Within the Southern M9.2 1964 Great Alaska Earthquake Asperity: Constraints From Receiver Functions Across a Spatially Dense Node Array
Kodiak Island is an exposed part of an accretionary complex along the Alaska-Aleutian subduction zone that formed as the Pacific plate subducted below the North American plate. Subduction of the Pacific plate beneath Alaska has produced more >M8 earthquakes than any other plate boundary system during the last ~100 yrs, including the 1964 M9.2 Great Alaska earthquake. Kodiak Island lies on a section of the subduction zone that ruptured in the 1964 event and experiences seismic tremors, suggesting multiple modes of plate interface slip. Unconsolidated sediment thickness and fluid distribution along the subduction zone interface are some of the factors thought to affect slip stability. 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 autonomous three-component 5-Hz Fairfield Nodal Zland geophones deployed at ~200-300 m spacing on northeastern Kodiak Island within the southern asperity of the 1964 M9.2 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.
Session: Crustal Imaging of High Seismic Hazard Regions
Type: Oral
Room: 209B
Date: 4/20/2023
Presentation Time: 08:00 AM (local time)
Presenting Author: Evans A. Onyango
Student Presenter: No
Additional Authors
Evans Onyango Presenting Author Corresponding Author eaonyango@alaska.edu University of Alaska Fairbanks |
Lindsay Worthington lworthington@unm.edu University of New Mexico |
Brandon Schmandt bschmandt@unm.edu University of New Mexico |
Geoffrey Abers abers@cornell.edu Cornell University |
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Subduction Zone Interface Structure Within the Southern M9.2 1964 Great Alaska Earthquake Asperity: Constraints From Receiver Functions Across a Spatially Dense Node Array
Category
Crustal Imaging of High Seismic Hazard Regions
Description