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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 ∼200–300 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.

 

Abstract The Alaska Amphibious Community Seismic Experiment (AACSE) is a shoreline-crossing passive- and active-source seismic experiment that took place from May 2018 through August 2019 along an ∼700  km long section of the Aleutian subduction zone spanning Kodiak Island and the Alaska Peninsula. The experiment featured 105 broadband seismometers; 30 were deployed onshore, and 75 were deployed offshore in Ocean Bottom Seismometer (OBS) packages. Additional strong-motion instruments were also deployed at six onshore seismic sites. Offshore OBS stretched from the outer rise across the trench to the shelf. OBSs in shallow water (<262  m depth) were deployed with a trawl-resistant shield, and deeper OBSs were unshielded. Additionally, a number of OBS-mounted strong-motion instruments, differential and absolute pressure gauges, hydrophones, and temperature and salinity sensors were deployed. OBSs were deployed on two cruises of the R/V Sikuliaq in May and July 2018 and retrieved on two cruises aboard the R/V Sikuliaq and R/V Langseth in August–September 2019. A complementary 398-instrument nodal seismometer array was deployed on Kodiak Island for four weeks in May–June 2019, and an active-source seismic survey on the R/V Langseth was arranged in June 2019 to shoot into the AACSE broadband network and the nodes. Additional underway data from cruises include seafloor bathymetry and sub-bottom profiles, with extra data collected near the rupture zone of the 2018 Mw 7.9 offshore-Kodiak earthquake. The AACSE network was deployed simultaneously with the EarthScope Transportable Array (TA) in Alaska, effectively densifying and extending the TA offshore in the region of the Alaska Peninsula. AACSE is a community experiment, and all data were made available publicly as soon as feasible in appropriate repositories. 

NORTH AMERICA’S LARGEST EARTHQUAKES and most powerful volcanic eruptions occur along the Alaska Peninsula subduction zone, a meeting of two tectonic plates that sweeps an arc across the North Pacific margin between Alaska and Russia. However, studies that would help us understand these hazards are few and far between in this remote, sparsely populated region. A major new shoreline- crossing community seismic experiment spans the Alaska Peninsula subduction zone, with the intention of filling gaps in our knowledge of this region. Information that we collect along this margin can provide direct information about many first- order questions about subduction zone processes that influence earthquakes and volcanism. 

North America’s largest earthquakes and most powerful volcanic eruptions occur along the Alaska Peninsula subduction zone, a meeting of two tectonic plates that sweeps an arc across the North Pacific margin between Alaska and Russia. However, studies that would help us understand these hazards are few and far between in this remote, sparsely populated region. A major shoreline-crossing community seismic experiment, now under way, spans the Alaska Peninsula subduction zone, with the intention of filling gaps in our knowledge of this region. Information that we collect along this margin can provide direct information about many firstorder questions about subduction zone processes that influence earthquakes and volcanism.