Repeating Glacial Seismicity at the Foundation Ice Stream, West Antarctica

We investigate the occurrence of glacial seismicity located near the grounding line of the Foundation Ice Stream and further upstream using continuous broadband seismic data collected by Polar Earth Observing Network (POLENET/A-NET) stations from 2014 to 2019. Through manual identification and cross-correlation analysis, ~3000 discrete icequakes are detected. Seismic event locations are predominantly constrained using backazimuth estimates derived from surface wave polarization analysis; however, for icequakes with at least 4 clear P- and/or S-wave arrivals, event locations are refined using the Hypoinverse earthquake location software. Preliminary local magnitude (ML) estimates range from 1.0 to 3.2. From the five years of seismic data analyzed here, a seasonal variability in event timing at the grounding line of the Foundation Ice Stream is apparent. The seismic events located near the grounding line occur almost exclusively between 21:00 - 01:00 UTC from November to February (i.e., approximately austral summer) and between 10:00 - 13:00 UTC from May to August (i.e., approximately austral winter). Periods of time where seismic events occur between both 21:00 - 01:00 UTC and 10:00 - 13:00 UTC occur every year and largely span from March to late-April and mid-August to late-October. This long-period variability in icequake timing is likely attributable to tidal and/or meteorological variations occurring throughout the year. More specifically, the long-period variability in icequake timing may be associated with a long-period tide, such as the solar semiannual tide (Ssa), modulating ice flow. In addition to the grounding line seismicity, we locate repeating icequakes west of the Patuxent Range, ~180 km upstream of the Foundation Ice Stream grounding line.