Geologists believe we may be witnessing the birth of a new subduction zone. Researchers have long puzzled over a plain, featureless area off the coast of Portugal. The seemingly-boring area stood out in 1969 when it triggered a massive earthquake that generated a tsunami. This was highly unusual — earthquakes don’t just happen in random areas. Most often, they take place in tectonically active areas, at the edges of tectonic plates. The correlation is so good that if you’d look at a global map of large earthquakes (see below), it looks like a map of tectonic plates. So why then did a 7.9 earthquake shake the coast of Portugal? João Duarte, a marine geologist from the Instituto Dom Luiz at the University of Lisbon, believes he has the answer. According to a recent study published by Duarte, the tectonic plate off Portugal’s coast might be peeling away from its top. ADVERTISEMENT Actively tectonic The Earth might seem static from our point of view, but from a geological perspective, it’s very active. Our planet’s crust is split into rigid plates which are always in motion to each other, at a rate of a few centimeters per year — which, in millions of years, can dramatically change the surface of the Earth. Naturally, when the plates are moving, they will sometimes be pushing against each other. If one plate is heavier than the other, it will slide beneath it — a process called subduction. We’re quite familiar with subduction as we’ve observed it and its effects in several parts of the world, but we’ve never actually seen it start. Until now. Get more science news like this... Join the ZME newsletter for amazing science news, features, and exclusive scoops. More than 40,000 subscribers can't be wrong. Daily Weekly I have read and agree to the terms & conditions. Leave this field empty if you're human: Suspicions of a potential subduction-related peeling event started after the 1969 earthquake, but it wasn’t until 2012 that researchers got a good view of the area, using seismic wave analysis (which works somewhat similar to an ultrasound). In 2018, Chiara Civiero, a postdoctoral researcher at University of Lisbon’s Instituto Dom Luiz, and her colleagues published a high-resolution peek into Earth in this region, and confirmed the discovery of the unusual blob. ADVERTISEMENT Now, Duarte found new evidence to support this theory in a seemingly innocuous geological layer, one which allows water to percolate (infiltrate) through. This water transforms the minerals inside the plate, transforming them into softer minerals, producing just enough weakness to allow the bottom of the plate to peel away. “Now we are 100-percent sure it’s there,” Duarte told Nationl Geographic. Other researchers found that above this deep body, which stretches 155 miles below the surface, tiny quakes seemed to tremble. Of course, work is still needed to confirm the find, but Duarte is confident. “It’s a big statement,” Duarte says of the conclusions, acknowledging that he and his team still have work to do. “Maybe this is not the solution to all the problems. But I think we have something new here.”<doc-sep>In 1969, a giant earthquake off the coast of Portugal kicked up a tsunami that killed over a dozen people. Some 200 years prior, an even larger earthquake hit the same area, killing around 100,000 people and destroying the city of Lisbon. Two earthquakes in the same spot over a couple hundred years is not cause for alarm. But what puzzled seismologists about these tremors was that they began in relatively flat beds of the ocean — away from any faults or cracks in the Earth's crust where tectonic plates slip past each other, releasing energy and causing earthquakes. So what's causing the rumbles under a seemingly quiet area? [In Photos: Ocean Hidden Beneath Earth's Crust] One idea is that a tectonic plate is peeling into two layers — the top peeling off the bottom layer — a phenomenon that has never been observed before, a group of scientists reported in April at the European Geosciences Union General Assembly held in Vienna. This peeling may be creating a new subduction zone, or an area in which one tectonic plate is rammed beneath another, according to their abstract. The peeling is likely driven by a water-absorbing layer in the middle of the tectonic plate, according to National Geographic. This layer might have undergone a geological process called serpentinization, in which water that seeps in through cracks causes a layer to transform into soft green minerals. Now, this transformed layer might be causing enough weakness in the plate for the bottom layer to peel away from the top layer. That peeling could lead to deep fractures that trigger a tiny subduction zone, National Geographic reported. This group isn't the first to propose this idea, but it's the first to provide some data on it. They tested their hypothesis with two-dimensional models, and their preliminary results showed that this type of activity is indeed possible — but is still yet to be proven. This research has not yet been published in a peer-reviewed journal. Originally published on Live Science.<doc-sep>Based on computer simulations, Duarte and his team surmised that two layers of one plate could be peeling apart, separated by a squishy middle layer that is becoming saturated with water in a process known as serpentinization. This is enabling the two layers to separate, with one sliding under the other, forming what is known as a subduction zone – the region where two plates collide, with one dominating and the other sliding underneath it.<doc-sep>
Portuguese researchers have put forward a new hypothesis to explain what’s happening underneath the Atlantic off the coast of Portugal. At a recent conference, they presented numerical simulations that suggest the bottom of the oceanic plate is peeling away from the top. If so, this might be the beginning of a new subduction zone and the possible eventual reunification of North-America and Europe into a single continent. This peeling phenomenon, known technically as delamination, was proposed to explain several features related to the region, known as the Horseshoe abyssal plain. As the name suggests, it is a flat region about 4.8 kilometers (3 miles) under water. It has no known tectonic fault, so geologically it shouldn’t be particularly active. Yet it is, and researchers think delamination may be the answer. Two major quakes shook the region over the last 300 years. First was the Great Lisbon earthquake of 1755, one of the deadliest in history, which took the lives of between 10,000 and 100,000 people. The latest is the 1969 Portugal earthquake, a 7.9 magnitude event where 13 people (11 in Morocco and two in Portugal) perished. The latter has led to international interest in the region, with many researchers investigating the area. In 2012, researchers used seismic waves to study the region. They found evidence of a curious dense structure deep below the crust. The presence of this mass was shown in a subsequent study from a different team, and other researchers have identified tiny quakes emanating from the mass that stretches 250 kilometers (155 miles) below the Earth’s crust. Researchers have been considering a possible explanation for decades. Dr João Duarte, a marine geologist at the University of Lisbon, and colleagues ran numerical simulations to show that a peeling tectonic plate is certainly possible. Duarte presented the findings at the European Geosciences Union meeting last month. “It’s a big statement,” Duarte told National Geographic. “Maybe this is not the solution to all the problems. But I think we have something new here.” Although the research is yet to be submitted for peer review, it has started several discussions in geological circles about the likelihood of such an event. The idea is certainly in line with another hotly debated scenario about the cyclical formation of a super-ocean every billion years or so. In that hypothesis, the Atlantic ocean should stop expanding in the future and begin to sink underneath the continental plates. Evidence of a delaminated oceanic plate would provide great support for the super-ocean cycle hypothesis. [H/T: National Geographic]