A study of seismicity within the Perunika Glacier on Livingston Island in Antarctica has revealed a variable frequency of ice shaking, possibly related to melting ice.
For more than 30 years, studies of glacial seismicity – the frequency of non-tectonic seismic events in ice – have focused on Greenland, and for good reason. Greenland’s “ice earthquakes,” as scientists call underground tremors in glaciers, are increasingly breaking records, raising alarms about the effects of melting glaciers and climate change.
At the opposite pole of Antarctica, seismicity is also largely driven by the movement and collapse of ice in the thick layer covering the continent. As a global phenomenon, ice shaking indicates a large correlation between climate change and ice mass, and ice shaking can serve as an indicator of the overall condition of glacial ice – more ice shaking, more melting. As part of an ongoing project, seismologist Gergana Georgieva of the Bulgarian Academy of Sciences and Sofia University and her colleagues are studying seismic activity in the Antarctic Perunica Glacier, located near the St. Clement of Ohrid Island base in Bulgaria on Livingstone Island.
Tracking Antarctic ice earthquakes
Antarctica is a remarkably seismically active region, and glacier behavior is crucial to understanding both base topography and climatic influences on the region.
There is one Bulgarian seismic station near Perunica Glacier that has been recording seismic events during the Australian summer since 2015. Beginning in January 2020, the station will collect data year-round. Such research has never been done in the area, Georgieva said. By monitoring these ice shocks, Georgieva’s team has accurately located more than 16,000 events – no easy feat with just one station. By accurately identifying the epicenters of ice shaking – a point on the Earth’s surface directly above where the seismic event occurred – scientists can better understand the origin of these curious earthquakes, their seasonal variability and changes over time.
Estimating epicenters and clusters
Georgieva and her team developed a localization code that calculated and mapped the epicenter of events that lasted from one to three seconds. In this code, a sophisticated algorithm determined the direction of the first incoming seismic wave in three dimensions (north/south, east/west, and vertical). Then, by calculating the difference between the first and second incoming seismic waves generated by the event, the code could accurately locate the epicenter. To test this process, Georgieva calculated the epicenter of several earthquakes recorded by both the Bulgarian seismic station and the Spanish research team in the area-the locations matched.
Through this localization process, the team obtained reliable data with which to study the frequency and distribution of ice shaking. “We traced the events that occurred in the glacier and then noticed three clusters of epicenters in different parts of the glacier,” says Georgieva. Two of these clusters of ice shaking corresponded to areas of the glacier known for high glacial flow rates, and the third cluster was located near Johnson Dock, another glacier terminus in the region.
More time, more events
Seismicity has also increased over the course of the study. “We don’t have enough data yet to understand how activity changes seasonally,” says Georgieva, “so this will be an important next step,” made possible by the year-round installation of the station. In addition to tracking changes in seasonal activity, Georgieva and her team will compare seismic data with long-term meteorological information to examine the relationship between seismicity and weather, which they hope to eventually link to climate.
“Each seismic station and each season of data collection will allow us to better understand changes in the region,” Georgieva said, “and allow us to learn about this glacier and others in the area at different time scales.”