Abstract
AbstractObservations of teleseismic earthquakes using broadband seismometers on the Ross Ice Shelf (RIS) must contend with environmental and structural processes that do not exist for land-sited seismometers. Important considerations are: (1) a broadband, multi-mode ambient wavefield excited by ocean gravity wave interactions with the ice shelf; (2) body wave reverberations produced by seismic impedance contrasts at the ice/water and water/seafloor interfaces and (3) decoupling of the solid Earth horizontal wavefield by the sub-shelf water column. We analyze seasonal and geographic variations in signal-to-noise ratios for teleseismic P-wave (0.5–2.0 s), S-wave (10–15 s) and surface wave (13–25 s) arrivals relative to the RIS noise field. We use ice and water layer reverberations generated by teleseismic P-waves to accurately estimate the sub-station thicknesses of these layers. We present observations consistent with the theoretically predicted transition of the water column from compressible to incompressible mechanics, relevant for vertically incident solid Earth waves with periods longer than 3 s. Finally, we observe symmetric-mode Lamb waves generated by teleseismic S-waves incident on the grounding zones. Despite their complexity, we conclude that teleseismic coda can be utilized for passive imaging of sub-shelf Earth structure, although longer deployments relative to conventional land-sited seismometers will be necessary to acquire adequate data.
Highlights
Multi-year seismic instrumentation of Antarctica has been historically sparse for regions not immediately accessible from the established science bases
We present a signal-to-noise and phenomenological analysis of 2 years of teleseismic earthquake signals recorded by a 34-station broadband seismic array deployed across the Ross Ice Shelf (RIS), Antarctica
Teleseismic observations in this environment must contend with a complex elastic and gravity wave displacement wavefield consisting of: (1) short period (0.4–4.0 s) ocean noise associated with shorter period microseism generation and/or direct ice front excitation; (2) primary and secondary microseisms; (3) flexuralgravity waves excited by infragravity and ocean swell waves; (4) water layer-decoupled P- and S-wave arrivals; (5) high-frequency (1–10 Hz) reverberations from the strong ice shelf basal and surface impedance contrasts and (6) intermediate to long period (10– 50 s) plate waves induced by oceanic and teleseismic forcings
Summary
Multi-year seismic instrumentation of Antarctica has been historically sparse for regions not immediately accessible from the established science bases. This largely reflects the engineering and logistical challenges of year-round seismograph operation under extreme environmental conditions and limited opportunities for maintenance and data recovery. Podolskiy and Walter, 2016; Aster and Winberry, 2017) and instrumentation advancements over the last two decades have resulted in a dramatic increase in available seismic data, driven by numerous deployments of long-term or permanent broadband seismic instruments in both West and East Antarctica (Anthony and others, 2015). Two key developments in particular have removed the scientific and technical barriers to long-term, broadband ice shelf seismology. Community advancements in power and other technologies have produced lightweight broadband seismographs that are capable of continuous operation throughout multiple Antarctic winters
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