Tidally-modulated icequakes reveal mechanisms governing rifting on Larsen C Ice Shelf, Antarctic Peninsula

Suture zones, formed in the wake of peninsulas, are known to stall rifts on the Larsen C Ice Shelf, stabilising the shelf by delaying mass calving events. What exactly these rifts are composed of, and therefore how they are able to stall rifts, has remained elusive. Here we present direct evidence for brittle deformation within a suture zone immediately ahead of a detained rift tip, as recorded by a dense array of 29 low-noise accelerometers and three geophones. 251 icequakes were identified to originate within the network, 108 of which were successfully relocated to show a concentration of seismicity within the suture zone’s interior ice. No events were observed in the lowermost 20 m of the shelf, indicative of a porous basal marine ice layer or crevasse/cavity. The magnitude-frequency distribution yielded a catalogue b-value = 1.20 ± 0.11. For events from which source mechanisms could be derived, there is a correlation between rising/falling tides and explosive/implosive events, respectively. Collectively, these results are indicative of tidally-driven infiltration of seawater into the suture through the rift tip which will act to corrode the suture and promote brittle failure. The time-integrated effect of this process as the rift advects downstream will eventually weaken the suture zone sufficiently to allow for the rift to propagate despite lower downstream stresses, limiting the stabilising role of sutures towards the calving front.