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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.
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RAPID: Response to the 29 July 2021 Chignik Earthquake
The July 2021 Chignik earthquake (M8.2) was the biggest earthquake in the US since 1965 (Rat Islands). It ruptured a segment of the megathrust offshore of the Alaska Peninsula, which last ruptured in 1938, although there are some differences. It is also the middle of the recent AACSE project, which deployed 30 PASSCAL Broadbands, 75 OBSs, and 398 Nodes in 2018-8, making it among the best-characterized megathrust segments. This dataset contains the on-shore seismic aftershock survey, where we reoccupy several AACSE sites on the Shumagin Islands, Alaska Peninsula and Kodiak, with one new deployment on the Semidi islands close to the epicenter. Stations are deployed from Kodiak or Chignik. Sites are deployed in early August 2021, within 2 weeks of the mainshock, and continue until May-June 2022 when they are recovered. All sites have compact broadband sensors and are powered by Air-Alkaline Cells, which are relatively winter- and bear-resistant. All data are to be made open as rapidly as possible.
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- Award ID(s):
- 2147438
- PAR ID:
- 10553222
- Publisher / Repository:
- International Federation of Digital Seismograph Networks
- Date Published:
- Format(s):
- Medium: X Size: 100000 MB Other: SEED data
- Size(s):
- 100000 MB
- Location:
- (East Bound Longitude:-151.464; North Bound Latitude:58.764; South Bound Latitude:53.744; West Bound Longitude:-161.308)
- Institution:
- Cornell University
- Sponsoring Org:
- National Science Foundation
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Abstract The Alaska Amphibious Community Seismic Experiment (AACSE) comprised 75 ocean-bottom seismometers and 30 land stations and covered about 650 km along the segment of the subduction zone that includes Kodiak Island, the Alaska Peninsula and the Shumagin Islands between May 2018 and September 2019. This unprecedented onshore-offshore dataset provided an opportunity to compile a greatly enhanced earthquake catalog for the region by both increasing the number of detected earthquakes and improving the accuracy of their source parameters. We use all available regional and AACSE campaign seismic data to compile an earthquake catalog for the region between Kodiak and the Shumagin Islands including the Alaska Peninsula (51° N–59° N, 148° W–163° W). We apply the same processing and reporting standards to additional picks and events as the Alaska Earthquake Center currently uses for compilation of the authoritative regional earthquake catalog. Over 7200 events (both newly detected and previously reported) have been processed with AACSE data. We added about 30% more events, 60% more phase picks, lowered the magnitude of completeness by about 0.2 on average across the region, and improved location errors. All data have been published in public data archives. In addition, we test the machine-learning earthquake detection and picking algorithm EarthquakeTransformer (EQT) on the AACSE seismic dataset, comparing EQT-determined P and S picks with the new catalog. EQT is entirely trained on land data, whereas AACSE is amphibious. Overall, EQT finds 59% of P and 63% of S arrivals in the catalog within 300 km epicentral distance. The percent of catalog picks detected by EQT varies inversely with earthquake epicentral distance, and EQT performs particularly poorly on data from earthquakes recorded by instruments in the outer rise.more » « less
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