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Local, regional, and distal recordings of seismic unrest at Taʻū Island volcano, American Samoa

Aaron Wech1 , Matt Haney1, Jefferson C. Chang2, Art Jolly2, Clara Yoon3, and Robert Skoumal4

  • Affiliations: 1 U.S. Geological Survey, Alaska Volcano Observatory, Anchorage, Alaska, USA 2 U.S. Geological Survey, Hawaiian Volcano Observatory, Hilo, Hawaii, USA 3 U.S. Geological Survey, Earthquake Science Center, Pasadena, California, USA 4 U.S. Geological Survey, Earthquake Science Center, Moffett Field, California, USA

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 123

  • Programme No: 2.1.33

  • Theme 2 > Session 1

Abstract

A seismic swarm near Taʻū Island, a volcanic island in eastern American Samoa, occurred from July to October 2022. The earliest unrest was noted as felt shaking reports in late July. The U.S. Geological Survey Hawaiian Volcano Observatory responded by installing temporary and then permanent seismometers to monitor the activity. This network variability made it difficult to characterize the earliest seismicity and contextualize the entire sequence to discriminate between an underlying tectonic or volcanic source. We analyze hydroacoustic detections from a hydrophone array near Wake Island, 4500 km northwest of Taʻū Island volcano. Using least-squares beamforming analysis, we create a catalog of T-wave detections from the direction of Taʻū Island to track the earthquakes. Both the rate and hydroacoustic pressures, which we interpret as a proxy for earthquake size, gradually increased from late July to August, peaking on August 19 (rate) and August 24 (size), before decreasing to background in late September. Minutes-long bursts of tremor were also recorded as local network data became available August 20. Tremor activity increased, peaking on August 25, before ending in early September. Bursts were band-limited to ~1-5 Hz and recorded as S waves at a regional station 250 km away. Our results do not constrain the tremor locations, but comparisons of earthquake and tremor reduced displacements recorded locally and regionally suggest a deeper tremor source. We interpret the increase in earthquake size and rate, together with the occurrence and relative depth of the tremor to reflect magmatic activity beneath Taʻū Island volcano.