Geophysical Research Letters | 2019
Tidal and Thermal Stresses Drive Seismicity Along a Major Ross Ice Shelf Rift
Abstract
18 Understanding deformation in ice shelves is necessary to evaluate the response of 19 ice shelves to thinning. We study microseismicity associated with ice shelf deformation 20 using 9 broadband seismographs deployed near a rift on the Ross Ice Shelf. From De21 cember 2014 November 2016, we detect 5948 icequakes generated by rift deformation. 22 Locations were determined for 2515 events using a least squares grid-search and double23 difference algorithm. Ocean swell, infragravity waves and a significant tsunami arrival 24 do not affect seismicity. Instead, seismicity correlates with tidal phase on diurnal timescales 25 and inversely correlates with air temperature on multi-day and seasonal timescales. Spa26 tial variability in tidal elevation tilts the ice shelf, and seismicity is concentrated while 27 the shelf slopes downward toward the ice front. During especially cold periods, thermal 28 stress and embrittlement enhance fracture along the rift. We propose that thermal stress 29 and tidally-driven gravitational stress produce rift seismicity with peak activity in the 30 winter. 31 Plain Language Summary 32 In Antarctica, large bodies of floating ice called ice shelves help prevent ice on land 33 from sliding into the ocean. To predict how Antarctica might respond to climate change, 34 we need to understand how ice shelves interact with the environment, including the at35 mosphere and the ocean. The largest ice shelf, the Ross Ice Shelf, is over 500,000 km 36 in area, making it the largest body of floating ice in the world. In this study, we deployed 37 9 seismographs, the same instruments used to study earthquakes, to monitor vibrations 38 and cracking within the Ross Ice Shelf over a two-year period. During that time, the in39 struments detected nearly 6000 fracture events along a 120 km long crack in the ice shelf. 40 We compared the timing of the cracking to air temperature data, ocean wave activity, 41 and tides to see whether these factors influenced the crackâs behavior. We found that 42 fracture occurs most frequently just after high tide during winter, when the air is very 43 cold. We also found that fracture at the rift is not triggered by ocean waves. This work 44 demonstrates that Antarctic ice shelves are very sensitive to the environment and high45 lights the need to continue studying them. 46