The seismic activity was the result of a massive landslide in Greenland's Dickson Fjord, which caused a 200-meter-high mega-tsunami that sloshed back and forth roughly 10,000 times in nine days. (Image credit: Wikipedia)
On September 16, 2020, a mega-tsunami struck Greenland's Dickson Fjord, leaving evidence of flooding up to 200 meters (650) high in some areas. Earthquake scientists around the world quickly noted something was off when seismic stations didn't pick up a frequency-rich rumble associated with earthquakes but rather a continuous hum with only a single frequency that lasted for nine days and reverberated around the globe.
Scientists have recently analyzed the seismic data from earthquake monitoring stations worldwide that uncovered another remarkable event – the mega-tsunami triggered a standing wave that oscillated back and forth in the Dickson Fjord, much like splashing around in a bathtub full of water, for over a week. The international team of scientists released their findings in a paper entitled "A rockslide-generated tsunami in a Greenland fjord rang Earth for 9 days."
The tsunami was triggered by a massive landslide, enough rock and ice to fill 10,000 Olympic-sized swimming pools, which triggered earthquake measuring stations from over 3,000 miles away and registered the event as a short signal. However, there was also a 10.88-millihertz (92-second) monochromatic very long period (VLP) signal that was produced by the sloshing wave of the mega-tsunami over the course of those nine days. "The mere fact that the VLP signal of a wave sloshing back and forth triggered by a landslide in a remote area of Greenland can be observed worldwide and for over a week is exciting," stated Angela Carrillo Ponce, a doctoral student at the German Research Centre for Geosciences. "That’s why we in seismology have been most concerned with this signal.”
Standing waves and VLPs are widely known occurrences and are normally associated with large break-offs from glaciers' edges; however the accompanying VLP that lasted for days is unusual. What is impressive about the event was how clear the VLP signal was being picked up by monitoring stations in Alaska, North America and even Germany. A comparison of satellite images confirmed the cause of the incident and how well the seismic signals correlated with the strength and direction of the rockfall that triggered the mega-tsunami.
“Our findings highlight how climate change is causing cascading, hazardous feedbacks between the cryosphere, hydrosphere, and lithosphere, state the scientists. They also hope their results can be used to detect and analyze similar events from the past and use that information to predict future events.
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