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1. Ocean-excited plate waves in the Ross and Pine Island Glacier ice shelves

   https://doi.org/10.1017/jog.2018.66  

   CHEN, ZHAO; BROMIRSKI, PETER D.; GERSTOFT, PETER; STEPHEN, RALPH A.; WIENS, DOUGLAS A.; ASTER, RICHARD C.; NYBLADE, ANDREW A. (October 2018, Journal of Glaciology)

   null (Ed.)

   Abstract Ice shelves play an important role in buttressing land ice from reaching the sea, thus restraining the rate of grounded ice loss. Long-period gravity-wave impacts excite vibrations in ice shelves that can expand pre-existing fractures and trigger iceberg calving. To investigate the spatial amplitude variability and propagation characteristics of these vibrations, a 34-station broadband seismic array was deployed on the Ross Ice Shelf (RIS) from November 2014 to November 2016. Two types of ice-shelf plate waves were identified with beamforming: flexural-gravity waves and extensional Lamb waves. Below 20 mHz, flexural-gravity waves dominate coherent signals across the array and propagate landward from the ice front at close to shallow-water gravity-wave speeds (~70 m s −1 ). In the 20–100 mHz band, extensional Lamb waves dominate and propagate at phase speeds ~3 km s −1 . Flexural-gravity and extensional Lamb waves were also observed by a 5-station broadband seismic array deployed on the Pine Island Glacier (PIG) ice shelf from January 2012 to December 2013, with flexural wave energy, also detected at the PIG in the 20–100 mHz band. Considering the ubiquitous presence of storm activity in the Southern Ocean and the similar observations at both the RIS and the PIG ice shelves, it is likely that most, if not all, West Antarctic ice shelves are subjected to similar gravity-wave excitation. 

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2. Ocean-excited plate waves in the Ross and Pine Island Glacier Ice Shelves

   https://doi.org/doi:/10.1017/jog.2018.66  

   Chen, Z. (July 2018, Journal of Glaciology)

   ABSTRACT. Ice shelves play an important role in buttressing land ice from reaching the sea, thus restrain- ing the rate of grounded ice loss. Long-period gravity-wave impacts excite vibrations in ice shelves that can expand pre-existing fractures and trigger iceberg calving. To investigate the spatial amplitude vari- ability and propagation characteristics of these vibrations, a 34-station broadband seismic array was deployed on the Ross Ice Shelf (RIS) from November 2014 to November 2016. Two types of ice-shelf plate waves were identified with beamforming: flexural-gravity waves and extensional Lamb waves. Below 20 mHz, flexural-gravity waves dominate coherent signals across the array and propagate land- ward from the ice front at close to shallow-water gravity-wave speeds (∼70 m s−1). In the 20–100 mHz band, extensional Lamb waves dominate and propagate at phase speeds ∼3 km s−1. Flexural- gravity and extensional Lamb waves were also observed by a 5-station broadband seismic array deployed on the Pine Island Glacier (PIG) ice shelf from January 2012 to December 2013, with flexural wave energy, also detected at the PIG in the 20–100 mHz band. Considering the ubiquitous presence of storm activity in the Southern Ocean and the similar observations at both the RIS and the PIG ice shelves, it is likely that most, if not all, West Antarctic ice shelves are subjected to similar gravity- wave excitation. 

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3. Ocean Surface Gravity Wave Excitation of Flexural Gravity and Extensional Lamb Waves in Ice Shelves

   https://doi.org/10.26443/seismica.v2i1.213  

   Abrahams, Lauren; Mierzejewski, Jose; Dunham, Eric; Bromirski, Peter D. (January 2023, Seismica)

   Flexure and extension of ice shelves in response to incident ocean surface gravity waves have been linked to iceberg calving, rift growth, and even disintegration of ice shelves. Most modeling studies utilize a plate bending model for the ice, focusing exclusively on flexural gravity waves. Ross Ice shelf seismic data shows not only flexural gravity waves, with dominantly vertical displacements, but also extensional Lamb waves, which propagate much faster with dominantly horizontal displacements. Our objective is to model the full-wave response of ice shelves, including ocean compressibility, ice elasticity, and gravity. Our model is a 2D vertical cross-section of the ice shelf and sub-shelf ocean cavity. We quantify the frequency-dependent excitation of flexural gravity and extensional Lamb waves and provide a quantitative theory for extensional Lamb wave generation by the horizontal force imparted by pressure changes on the vertical ice shelf edge exerted by gravity waves. Our model predicts a horizontal to vertical displacement ratio that increases with decreasing frequency, with ratio equal to unity at ~0.001 Hz. Furthermore, in the very long period band (<0.003 Hz), tilt from flexural gravity waves provides an order of magnitude larger contribution to seismometer horizontal components than horizontal displacements from extensional Lamb waves. 

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4. Ocean surface gravity wave excitation of flexural gravity and extensional Lamb waves in ice shelves

   https://doi.org/10.31223/X5GW60  

   Abrahams, L. S. (August 2022, Earth ArXiv)
5. Resonance excitation of atmospheric waves by vibration of the ground, ocean surface, and ice shelves

   https://doi.org/EGU2018/EGU2018-5584  

   Goin, O. A.; Zabotin, N. (January 2018, Geophysical research abstracts)

   null (Ed.)

   Atmosphere is known to respond in a resonant way to broad-band excitation associated with earthquakes, volcano eruptions, and convective storms. The resonances are observed via their ionospheric manifestations using HF Doppler radars, airglow observations, and the GPS-TEC technique and are seen as narrow frequency bands of greatly amplified oscillations. The resonances are normal modes of an atmospheric waveguide and occur at such frequencies that an acoustic-gravity wave, which is radiated at the ground level and is reflected from a turning point in the thermosphere or upper mesosphere, upon return to the ground level satisfies boundary conditions on the ground. Typically, the resonances correspond to near-vertical AGW propagation and have periods of about 3–5 minutes. Although the resonances are usually referred to as acoustic resonances, buoyancy effects are not negligible at such frequencies. The resonances correspond to most efficient coupling between atmosphere and its lower boundary and are promising for detection of such coupling. From the remote sensing prospective, the resonances are potentially significant because their frequencies are sensitive to variations in the vertical profile of neutral temperature up to thermospheric altitudes and to boundary conditions on the lower boundary, such as differences between the boundary conditions on the solid earth, ocean surface, and a finite ice layer overlying solid Earth or the ocean. Using recently developed consistent WKB approximation for acoustic-gravity waves, this paper investigates theoretically excitation of atmospheric resonances and quantifies the effects of buoyancy and non-vertical propagation, including the contribution of the Berry phase. Different kinds of atmospheric resonances are identified depending on the type of surface waves, including flexural waves in ice shelves, that are responsible for oscillations at the ground or sea level. 

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