Ar-Rehman

Seismic events have been detected beneath Antarctica’s Doomsday Glacier

Hundreds of hidden earthquakes discovered beneath Antarctica, and they're happening in a very odd location. Antarctica was long thought to be seismically calm, but new technology makes it possible to detect unexpected types of earthquakes beneath the ice. Hundreds of previously overlooked seismic events have been detected beneath Antarctica, including 245 near the marine edge of the Thwaites Glacier. Many appear to be glacial earthquakes caused when huge icebergs break off, capsize and collide with the glacier. The surge in activity coincided with a period when Thwaites was flowing faster toward the ocean, hinting that changing ocean conditions may be destabilizing the ice. Massive icebergs break off from the glacier edge, roll over or capsize, and slam back into the main ice body. This violent collision sends strong mechanical vibrations and low-frequency seismic waves through the ground. These events stayed hidden because they do not produce the high-frequency waves typical of tectonic earthquakes, making them invisible to standard global sensor networks. Researchers analyzed seismic data recorded between 2010 and 2023.Findings: Out of 362 total glacial earthquakes detected across Antarctica during this period, 245 were concentrated right at the edge of the Doomsday Glacier. The study was conducted by Thanh-Son Pham from the Australian National University.

The surge in seismic activity lined up with periods when the glacier was flowing faster into the ocean. Thwaites Glacier holds enough ice to raise global sea levels significantly if it collapses completely, making these hidden tremors a crucial warning sign of structural change driven by warming ocean forces. Glacial earthquakes are a special type of earthquake generated in cold, icy regions. First discovered in the northern hemisphere more than 20 years ago, these quakes occur when huge chunks of ice fall from glaciers into the sea. Until now, only a very few have been found in the Antarctic. In a study, evidence found for hundreds of these quakes in Antarctica, mostly at the ocean end of the Thwaites Glacier, the so-called Doomsday Glacier which could send sea levels rising rapidly if it were to collapse. Artificial intelligence (AI) has revealed hundreds of previously unknown earthquakes beneath the East Antarctic Ice Sheet, including some in an unexpected place: in the middle of a tectonic plate, far from a plate boundary. The findings reveal that Antarctica is more seismically active than previously thought and new technologies can help to uncover hidden earthquakes in surprising locations.

In the new study, scientists used machine learning, a type of AI, to reanalyze seismic data taken from 49 seismic stations over the past two decades: one dataset from 2001 to 2004, and another from 2012 to 2015. The data revealed over 500 previously unrecognized earthquakes about 60 to 90 miles (100 to 150 km's) beneath David Glacier, which stretches nearly 700 miles (1,100 km's), bridging East and West Antarctica. This major outlet glacier drains about 4% of the East Antarctic Ice Sheet into the ocean, and its ice has thinned over the past several thousand years. A glacial earthquake is created when tall, thin icebergs fall off the end of a glacier into the ocean. When these icebergs capsize, they clash violently with the “mother” glacier. The clash generates strong mechanical ground vibrations, or seismic waves, which propagate thousands of km's from the origin. What makes glacial earthquakes unique is that they do not generate any high-frequency seismic waves. These waves play a vital role in the detection and location of typical seismic sources, such as earthquakes, volcanoes and nuclear explosions. Due to this difference, glacial earthquakes were only discovered relatively recently, despite other seismic sources having been documented routinely for several decades. Most glacial earthquakes detected so far have been located near the ends of glaciers in Greenland, the largest ice cap in the northern hemisphere. Earthquakes over 50 miles (80 km) deep are called intermediate-depth earthquakes. This type of earthquake is typically seen only at tectonic plate boundaries, specifically subduction zones, where one tectonic plate dives beneath another. Yet the study showed that these earthquakes are happening in the middle of the tectonic plate, far from active plate boundaries.

The Greenland glacial earthquakes are relatively large in magnitude. The largest ones are similar in size to those caused by nuclear tests conducted by North Korea in the past two decades. As such, they have been detected by a high-quality, continuously operating seismic monitoring network worldwide. The Greenland events vary with the seasons, occurring more often in late summer. They have also become more common in recent decades. The signs may be associated with a faster rate of global warming in the polar regions. Although Antarctica is the largest ice sheet on Earth, direct evidence of glacial earthquakes caused by capsizing icebergs there has been elusive. Most previous attempts to detect Antarctic glacial earthquakes used the worldwide network of seismic detectors. However, if Antarctic glacial earthquakes are of much lower magnitude than those in Greenland, the global network may not detect them. "The earthquakes occur where the cold, rigid crust and upper mantle beneath East Antarctica meets warmer, softer rock beneath West Antarctica, and this contrast creates an abrupt change in tectonic strength," Long Ho, a University of Alabama geologist and first author of the new paper, said. The detected earthquakes have magnitudes ranging from 1.6 to 3.5. The warm, buoyant material of the upper mantle extends beyond the edges of David Glacier from below, uplifting the edges of the nearby crust and bending them, and this concentrated stress causes the ground to shake, Ho explained.

It was surprising to find so many earthquakes at these depths, far from plate boundaries, Ho said, but similar earthquakes may be occurring in other geographic regions and going unnoticed given their small magnitudes. AI could help to identify those hidden quakes by reanalyzing past seismic data. In the study, seismic stations in Antarctica itself to look for signs of these quakes. It turned up more than 360 glacier seismic events, most of which are not yet included in any earthquake catalogue. The events detected were in two clusters, near Thwaites and Pine Island glaciers. These glaciers have been the largest sources of sea-level rise from Antarctica. Thwaites Glacier is sometimes known as the Doomsday Glacier. If it were to collapse completely it would raise global sea levels by 3 metres, and it also has the potential to fall apart rapidly. About two-thirds of the events detected were located near the marine end of Thwaites. Most of these events are likely glacial earthquakes due to capsizing icebergs. The strongest driver of such events does not appear to be the annual oscillation of warm air temperatures which drives the seasonal behaviour of Greenland glacier earthquakes. Instead, the most prolific period of glacial earthquakes at Thwaites, between 2018 and 2020, coincides with a period of accelerated flow of the glacier’s ice tongue towards the sea. The ice-tongue speed-up period was independently confirmed by satellite observations. This speed-up could have been caused by ocean conditions, the effect of which is not yet well understood.

Deep earthquakes result from bending and flexure at the boundary between East and West Antarctica, beneath David Glacier. "As machine-learning tools continue to improve, they could reveal that deep, continental-interior earthquakes are more common than currently recognized," Ho said. "If so, the role of such events within the plate tectonics framework may need to be re-evaluated." The results also show that Antarctica is more dynamic than previously thought. The data from this is now yielding new results as modern techniques have been developed to analyze the data. The findings suggest the short-term scale impact of ocean states on the stability of marine-terminating glaciers. This is worth further exploration to assess the potential contribution of the glacier to future sea-level rise. The second largest cluster of detections occurred near the Pine Island Glacier. However, these were consistently located 60–80 km's from the waterfront, so they are not likely to have been caused by capsizing icebergs. These events remain puzzling and require follow-up research. The detected earthquakes are not strong enough to threaten the overlying ice sheets or the Antarctic ecosystem, so the research team is not concerned about that. Antarctica’s sudden sea ice loss is one of the most extreme and confusing events in the modern climate record. Scientists now know why it's happening. The detection of glacial earthquakes associated with iceberg calving at Thwaites Glacier could help answer several important research questions. These include a fundamental question about the potential instability of the Thwaites Glacier due to the interaction of the ocean, ice and solid ground near where it meets the sea.

Better understanding may hold the key to resolving the current large uncertainty in the projected sea-level rise over the next couple of centuries. To explore how the enormous weight of the Antarctic Ice Sheet might contribute to the location of earthquakes, and how changes in the ice sheet could affect underlying seismic activity. It's still puzzling that seismic activity is concentrated at David Glacier rather than spread along the mountains in this region, the answer could be linked to the recent history of the ice sheet growing and shrinking, or to a longer history of the ice sheet eroding. However, work like this is continued and expanded, to help us understand the history and improve our understanding of possible futures.