A report in The Seismic Record reveals that the event triggered a week-long oscillating wave, or seiche, in Dickson Fjord.
Angela Carrillo-Ponce of the GFZ German Research Centre for Geoscience and her team identified two distinct seismic signals from the event: a high-energy signal from the colossal rockslide that initiated the tsunami, and a very long-period (VLP) signal that persisted for over a week.
The VLP signal-detectable up to 5000 kilometers away-suggests that the landslide and ensuing tsunami generated a seiche, a standing wave that oscillated for days between the shores of Dickson Fjord.
"The fact that the signal of a rockslide-triggered sloshing wave in a remote area of Greenland can be observed worldwide and for over a week is exciting, and as seismologists this signal was what mostly caught our attention," said Carrillo-Ponce.
"The analysis of the seismic signal can give us some answers regarding the processes involved and may even lead to improved monitoring of similar events in the future. If we had not studied this event seismically, then we would not have known about the seiche produced in the fjord system," she added.
These findings are expected to aid researchers studying the effects of landslides in Greenland and similar regions where global warming and permafrost loss are causing increased instability in rocky slopes and glaciers.
Recent tsunamis in western Greenland have had devastating outcomes, including the 2017 Karrat Fjord event where an avalanche-induced tsunami flooded the village of Nuugaatsiaq, claiming four lives. Additionally, megatsunamis exceeding 100 meters in height have reached Europe from Greenland's eastern coast.
The 16 September 2023 megatsunami occurred in Dickson Fjord, a remote area of East Greenland, first noticed via social media and reports of waves impacting a military installation on Ella Island.
Carrillo-Ponce and her colleagues combined seismic data with satellite imagery to accurately pinpoint and reconstruct the sequence of events.
By analyzing the initial high-energy seismic signal and satellite images showing a missing rock section along a cliff in Dickson Fjord, they traced the landslide's path, which incorporated glacier ice, turning into a mixed rock-ice avalanche before hitting the water. The resulting megatsunami reached over 200 meters near the impact site and averaged 60 meters along a 10-kilometer stretch of the fjord.
"While we were able to obtain information on the direction and magnitude of the force exerted by the landslide, we do not have data to investigate the original cause of the landslide," Carrillo-Ponce said.
The researchers found that the strength, radiation pattern, and duration of the subsequent VLP seismic signal indicated the creation of a prolonged seiche in the fjord.
VLP signals have been observed in Greenland before, usually linked to iceberg collapses caused by glacial earthquakes. "In our case we observed a VLP signal too, but the main difference is the long duration," Carrillo-Ponce explained. "It is quite impressive to see that we could use good-quality data from stations located as far as Germany, Alaska and North America, and that those records were strong enough for at least one week."
The researchers believe their approach could help study similar past events and explore potential connections to climate and environmental changes.
"We have compared our results with remote sensing data to validate our solutions, and our study shows that the force produced by the signals is well resolved," Carrillo-Ponce said. "Therefore it becomes a useful analysis as seismic signals contain information on the type of source generating the signal and how the energy is radiated."
Research Report:The 16 September 2023 Greenland Megatsunami: Analysis and Modeling of the Source and a Week-Long, Monochromatic Seismic Signal
Related Links
Seismological Society of America
Bringing Order To A World Of Disasters
When the Earth Quakes
A world of storm and tempest
| Subscribe Free To Our Daily Newsletters |
| Subscribe Free To Our Daily Newsletters |
