Glacial earthquakes at Jakobshavn Glacier: Improved Detections and Dynamic Effects

Abstract:

From calving events to basal sliding to water movements, cryoseismology provides insight into various processes in glaciated regions at timescales that remote sensing often cannot. Glacial earthquakes — minute-long low-frequency seismic signals generated by calving events — may help us understand the short term dynamics of tidewater glaciers as they rapidly retreat in a warming climate. Recent work (Olsen and Nettles, 2019) demonstrating the existence of smaller magnitude glacial earthquakes suggests that glacial earthquake counts may not be accurately represented in the Global CMT catalogue. We develop a matched-filter detection approach with 20 template events from 2012 and 2013, and apply the approach to re-evaluate and expand the catalogue for Jakobshavn glacier in West Greenland, which drains approximately 7% of the Greenland ice sheet. Sixteen of the templates are the largest magnitude events on record, while four are small amplitude events that happen within 15 minute of a large event. We first apply our method to seismic records at ILULI and JIG1 stations over a 6 month period in 2012 for comparison to the CMT glacial earthquake catalogue. In 2012, we detect over 60 additional events with a 4% false detection rate. Next, in order to better understand the relationship between these events and the glacier dynamics that are driving them, we consider a more recent period starting in 2018 with two additional stations (JIG2 and JIG3) and other available records of glacier change. We calculate the magnitudes of detected events and the cumulative seismic moment to constrain ice loss. Additionally, we compare the timing of the glacial earthquakes to records of glacier velocity from TerraSAR-X and TanDEM-X satellites, and show that higher glacier terminus velocities correlate to higher glacial earthquake frequency. We also show the preliminary results of a comparison to records of ocean tide changes from GNSS-Reflectometry to investigate the effect of tidal forcing on glacial earthquakes occurrence and characteristics. Our results suggest that improved glacial earthquake detection and characterization could provide constraints on frontal ablation at tidewater glaciers.