Tidally Induced Icequake Swarms at the Grounded Margins of the Ross Ice Shelf, Antarctica

Session: Environmental and Near Surface Seismology: From Glaciers and Rivers to Engineered Structures and Beyond [Poster]
Type: Poster
Date: 4/29/2020
Time: 08:00 AM
Room: Ballroom
Description: 

The broadband RIS/DRIS seismic network deployed across the Ross Ice Shelf, Antarctica from late 2015 to early 2017 recorded persistent icequake swarms that correlate with ocean tides. Swarms are observed only at stations near the grounded margins, occur year-round, repeat diurnally during falling tides and feature event families with highly similar waveforms. A single swarm typically consists of 1000’s of detectable icequakes over the course of several hours. Signals are mainly surface wave energy in the ~4-10 Hz band with preceding weaker body wave energy in the ~20-30 Hz band. During a swarm, peak frequencies migrate slightly lower and event amplitude increases. We create an initial catalog of icequakes using STA/LTA detection to identify body and surface wave arrivals, then match arrival pairs to define an event. The regional-scale station spacing of the network requires a single-station methodology for locating sources. Back-azimuth is estimated from the Rayleigh polarization of the surface waves. Distance is estimated by arrival time differences between body and surface waves. Icequakes regularly show surface wave dispersion which may provide an additional constraint on distance. Event metrics (magnitude, peak frequency, etc.) are added to the catalog and aggregate swarm population statistics are computed. We interpret that surface crevasse activity in high-strain marginal regions is the source for the main event population. This is supported by coincident timing with high extensional stress during falling tides and by the high ratio of surface to body wave energy. This can be further supported by comparing observed signals to synthetic seismograms modelling near-surface and basal sources. A second much smaller population of swarms occurs at high stands (only during spring tides) and is distinguished by a lower ratio of surface to body wave energy, suggesting of a deeper (possibly basal) mechanism. Studying these swarms offers insight into marginal ice shelf dynamics and brittle properties for the Ross Ice Shelf.

Presenting Author: Hank M. Cole

Authors