1F (2025-2027): Seismic study of flexural-gravity-wave band gaps, Bragg scattering and ice-damage processes on the McMurdo Ice Shelf

• University of Chicago

Theoretical studies show that ice shelves that are rumpled or otherwise disturbed by spatially periodic thickness and/or mechanical property variations cause incoming flexural-gravity waves (also known as asymmetric Lamb waves) generated by the ocean and meteorological conditions elsewhere to be subject to Bragg scattering. This makes rumpled areas of the ice shelf "opaque" to the transmission of incoming f-g waves, and for them to display band gaps in their local flexural-gravity wave eigenmodes. Bragg scattering is more commonly known by its influence on the reflection of electromagnetic waves by periodic structures such as atoms in a crystal. This scattering concept is also well documented for ocean waves that encounter large-scale ripples on the sea bed near shores. In fact, coastal engineering schemes exist for building periodic sand-bars on sea beds in soft river-estuary regions, where literal sea-walls are hard to build, as a means of protecting shore structures from damage due to incoming waves. The significance of Bragg scattering and band gaps on an ice shelf is to substantially protect the ice shelf from flexure-damage (fracture) due to the prolonged excitement of ambient flexural-gravity wave impact. This means that the process to be studied has an influence on ice-shelf stability and sea level rise. Our project seeks support to deploy 5 seismometers along a 2 km km transect of the "rumpled" part of the McMurdo Ice Shelf near Scott Base (the NZ Antarctic Program station). The seismometers will be operated from November of 2024 to January of 2025 (assuming year 1 of the field project will be during the 2024/5 field season). At the end of January 2025 4 seismometers will be recovered, leaving one seismometer to operate until late January or early February of 2026 to allow a full year of observation (including the better part of two summer seasons). Depending on data gathered during the November 2024 to 2025 timeframe, another summer season deployment of the full 5-seismometer array will be done during the 2025/6 season. The seismometers requested will be broad band and capable of measuring seismic signals between 100 Hz and 0.01 Hz. Rugged sensors that can be deployed in a snow pit or buried in a shallow surface drill hole would be ideal. The seismic array to operate during the summer of year 1 (Nov. to early Feb., 2024/5) will be deployed by the PI's of the project (if funded) and their graduate students. To assist the USAP in reducing station populations, the effort of recovering the 4 "non-winter-over" stations in late January or early February of 2025, and the setting up of the 5th sensor to operate over winter, can be done by the PASSCAL representative in McMurdo. If this is the case, only the sensors and their support materials (digitizers and power supplies) need be picked up, and any associated field infrastructure (poles, pits, etc.) can be left for the PI's to pick up during their deployment in year 2.

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