Tidally Induced Cryoseismicity Observed Along the Periphery of the Ross Ice Shelf, Antarctica

Date: 4/26/2019

Time: 06:00 PM

Room: Grand Ballroom

Repeating swarms of local cryoseismic events were recorded by a broadband seismic network deployed on the Ross Ice Shelf, Antarctica from late 2014 to early 2017. The swarms are observed exclusively at stations near the grounding line. They occur in phase with modeled tidal cycles and produce peak seismicity with an approximate 90° phase lag following high tide. Swarms commonly persist for over 6 hours, gradually increasing in event intensity and frequency before terminating abruptly to pre-swarm background levels. Total swarm intensity correlates with the modeled tide range, which is highly variable in the Ross Sea. Swarm seismicity may also be sensitive to seasonal changes in environmental conditions. Waveforms also show that events originate from multiple distinct source regions. Signals from these regions trigger repeatedly, resulting in families of events with similar seismograms. Our work aims to locate the source regions and determine their seismogenic processes. Particle motion analysis shows that the seismograms are dominated by Rayleigh waves, so we use surface wave analysis to constrain their mechanism and location. Given azimuthal and perhaps range (determined from dispersion) information, source regions can be constrained then evaluated via satellite imagery for association with surface features. Preliminary results suggest a shallow source possibly related to crevassing, but other candidate mechanisms will continue to be explored. Additionally, we will analyze swarm aggregate metrics and statistics to quantitatively examine how mechanisms vary spatially and evolve over time and through tidal variations. We hypothesize that these swarms arise from increasing tensile stresses during falling tide as bending occurs near the grounded margins. We anticipate that these observations will provide further insight into the dynamics and brittle properties of the ice shelf. This should also guide efforts to observe and utilize this phenomenon to improve understanding of other tidally stressed glacial masses.

Presenting Author: Hank Cole

Authors