FY 2025

Detection and analysis of Aleutian Arc seismicity (2022–2023) using an autonomous hydrophone array

Ingale, V.V., G. Tepp, R.P. Dziak, and R. Parnell-Turner

Geochem. Geophys. Geosyst., 26(8), e2025GC012320, doi: 10.1029/2025GC012320, View open access article at AGU/Wiley (external link) (2025)

The Aleutian trench, extending from the Gulf of Alaska to Kamchatka, marks the subduction boundary between the Pacific and North-American plates. It hosts the Aleutian Islands, one of Earth's most significant volcanic arcs, with 52 historically active volcanoes. Given the long history of eruptions and strong earthquake-induced tsunamis that pose hazards to Aleutian communities, studying this area is essential for assessing geohazards and subduction zone processes. To investigate submarine volcanism and seismicity along the western Aleutian Islands, four autonomous underwater hydrophones (AUH) were deployed in June 2022 for 12 months ∼100 km north of Adak Island. The AUHs were moored at depth of ∼500 m in a diamond-shaped array with 10 km spacing. The AUHs recorded different types of acoustic signal packets (events), including long-duration (∼40 s) spindle-shaped T-phases with frequencies <60 Hz, that are characteristics of tectonic earthquakes and short-duration (∼10 s), impulsive signals with a wide range of frequencies (40–100 Hz) were observed, peaking in activity during March 2023, that are associated with shallow seismic events. We characterized all hydroacoustic events by their temporal distribution, back-azimuths, rise time, and received level to establish acoustic signal categories based on the likely source mechanisms. By comparing hydroacoustic detections with a land-based earthquake catalog, we observe that short-duration events originated from seismic unrest beneath Tanaga Island. The temporal distribution of magnitudes and depths of seismic events, coupled with rise times and received levels of matched hydroacoustic signals, suggests that the seismic unrest is linked to magma transport at shallow depths beneath Tanaga Island.

Plain Language Summary. The Aleutian Island arc, formed by the convergence of two tectonic plates in the north Pacific, hosts several active volcanoes. These volcanic centers produce seismicity through mechanisms such as subsurface magma movement, volcanic eruption, and subduction processes. But seismic monitoring is difficult due to their remoteness and the limited availability of land-based stations. We analyze a year-long hydroacoustic data recorded on an array of four hydrophones moored in the Bering Sea. We detected 4,586 hydroacoustic events mainly consisting of two types: long duration (∼40 s) T-phases and short-duration (∼10 s) impulsive signals. These events were characterized by temporal distribution, source direction, wave shape, and acoustic energy. After correlating these events with the records from the United States Geological Survey earthquake catalog, we observed that the impulsive signals are primarily associated with the seismic unrest beneath the Tanaga volcanic center, situated in the central western part of the volcanic arc. We observed distinct periods of higher seismic activity in both the hydroacoustic and seismic catalogs, which we attribute to subsurface magmatic processes occurring during the Tanaga unrest between November 2022 and March 2023.