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MS Plan A Defense: A Comparative Study of the Tsunamis from the 2021 and 2023 Loyalty Islands Mw 7.7 Thrust-Fault and Normal-Fault Earthquakes
July 29 @ 1:00 pm - 2:00 pm
William Robert
Master’s Student
Department of Ocean and Resources Engineering
University of Hawai’i at Mānoa
**This defense will be held both in person (POST 723) and over Zoom**
Meeting ID: 940 0074 6297
Passcode: WillMS
https://hawaii.zoom.us/j/94000746297
The Vanuatu Subduction Zone is an active tectonic region with a history of moderate to large tsunamigenic earthquakes. While over 40 earthquakes of Mw 7.0 or stronger have occurred along the New Hebrides trench within the past quarter-century, the subduction dynamics, tsunamigenic potential, and coastal risk of tsunamigenic earthquakes emanating from the southern trench remain understudied. We compare the tsunami signals from the 2021 and 2023 Mw 7.7 thrust-fault and normal-fault earthquakes along the South New Hebrides Trench. The 2021 megathrust earthquake was determined to have a relatively shallow slip patch with a focal depth of 10.0 km. The 2023 outer-rise normal-faulting earthquake occurred westward of the 2021 event at a depth of 18.1 km. The comparable moment magnitude and proximity of their epicenters provide an opportunity to examine the influence of fault mechanisms at the Southern New Hebrides Trench on the tsunami waveform throughout the Southwest Pacific. The preferred finite-fault rupture models for each earthquake event were determined through iterative inversion of teleseismic P-waves and forward modeling of the tsunami waveform to match measurements at DART and coastal tide gauge stations. Analysis of the computed tsunami waveforms reveals that the 2021 and 2023 tsunamis are primarily influenced by the location of the seafloor deformation with respect to major bathymetric features in the near field. The width of seafloor deformation and subsequent period of tsunami waves have a strong effect on the far-field pattern of energy lobes, but the overall wave patterns exhibit similarities because the effects of bathymetry and resonance dominate at a larger scale.