자신의 바다를 먹고 있는 지구 VIDEO: The Earth Is Eating Its Own Oceans
The Earth Is Eating Its Own Oceans
By Stephanie Pappas, Live Science Contributor | November 14, 2018 04:18pm ET
As Earth's tectonic plates dive beneath one another, they drag three times as much water into the planet's interior as previously thought.
The Earth Is Eating Its Own Oceans
At earthquake-prone subduction zones, where tectonic plates dive beneath one another, massive amounts of
sea water are dragged into the planet's interior, a new study has revealed. Credit: visdia/Getty
자신의 바다를 먹고 있는 지구 섭입대(subduction zone), 3배나 많은 물 흡수해 지진 발생 가능성도 높여 지구의 지각판이 서로 아래로 내려갈 때, 그들은 이전에 생각했던 것보다 3배나 많은 물을 지구 내부로 끌어온다. 오늘(11월 14일) 네이처지에 실렸던 신간 논문의 결과다. 연구원들은 태평양 판이 필리핀 판 아래로 미끄러지고 있는 마리아나 해구의 지진 발생 지역에서 얼마나 많은 물이 깊은 바위들에 흡수되는지를 추정할 수 있었다. 이 발견은 지구의 깊은 물의 순환을 이해하는 데 큰 영향을 끼치고 있으며, 콜럼비아 대학의 라몬트-도어 지구 관측소의 해양 지질학과 지질물리학 연구원 도나 실링턴은 이 내용을 신문 기고 글과 함께 게재했다. "지구의 표면 아래에 있는 물은 마그마의 형성에 기여할 수 있고 결함에 활성화시켜 지진의 가능성을 높일 수 있다"고 실링턴은 말했다. * 섭입대 subduction zone 판구조론에서는 판의 이동에 의해 판과 판이 서로 충돌하는 경우가 나타나는데, 이때 해양판과 대륙판이 충돌할 경우 상대적으로 무거운 해양판이 가벼운 대륙판 밑으로 밀려들어가는데, 이러한 작용이 일어나는 곳을 섭입대라고 한다. 일반적으로 대륙 연변부의 깊은 해저인 해구는 이러한 섭입작용에 의해 형성된 것이며, 이러한 섭입작용에 의해서 부근의 지층은 심한 교란과 접촉변성작용이 일어나고, 부근지역에는 판의 충돌에 의한 에너지가 분출되면서 습곡산맥, 화산지형 등이 형성된다. 지진활동도 천발지진에서 심발지진에 이르기까지 다양하게 발생한다. [네이버 지식백과] geo.cornell.edu 황기철 콘페이퍼 에디터 큐레이터 Ki Cheol Hwang, conpaper editor, curator |
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Those are the results of a new paper published today (Nov. 14) in the journal Nature. Using the natural seismic rumblings of the earthquake-prone subduction zone at the Marianas trench, where the Pacific plate is sliding beneath the Philippine plate, researchers were able to estimate how much water gets incorporated into the rocks that dive deep below the surface. [In Photos: Ocean Hidden Beneath Earth's Surface]
The find has major ramifications for understanding Earth's deep water cycle, wrote marine geology and geophysics researcher Donna Shillington of the Lamont-Doherty Earth Observatory at Columbia University in an op-ed accompanying the new paper. Water beneath the surface of the Earth can contribute to the development of magma and can lubricate faults, making earthquakes more likely, wrote Shillington, who was not involved in the new research.
The deep water cycle
Water is stored in the crystalline structure of minerals, Shillington wrote. The liquid gets incorporated into the Earth's crust both when brand-new, piping-hot oceanic plates form and when the same plates bend and crack as they grind under their neighbors. This latter process, called subduction, is the only way water penetrates deep into the crust and mantle, but little is known about how much water moves during the process, study leader Chen Cai of Washington University in St. Louis and his colleagues wrote in their new paper.
"Before we did this study, every researcher knew that water must be carried down by the subducting slab," Cai told Live Science. "But they just didn't know how much water."
The researchers used data picked up by a network of seismic sensors positioned around the central Marianas Trench in the western Pacific Ocean. The deepest part of the trench is nearly 7 miles (11 kilometers) below sea level. The sensors detect earthquakes and the echoes of earthquakes ringing through Earth's crust like a bell. Cai and his team tracked how fast those temblors traveled: A slowdown in velocity, he said, would indicate water-filled fractures in rocks and "hydrated" minerals that lock up water within their crystals.
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Missing water
The researchers observed such slowdowns deep into the crust, some 18 miles (30 km) below the surface, Cai said. Using the measured velocities, along with the known temperatures and pressures found there, the team calculated that the subduction zones pull 3 billion teragrams of water into the crust every million years (a teragram is a billion kilograms).
Seawater is heavy; a cube of this water 1 meter (3.3 feet) long on each side would weigh 1,024 kilograms (2,250 lbs.). But still, the amount pulled down by subduction zones is mind-boggling. It's also three times as much water as subduction zones were previously estimated to take in, Cai said.
And that raises some questions: The water that goes down must come up, usually in the contents of volcanic eruptions. The new estimate of how much water is going down is larger than estimates of how much is being emitted by volcanos, meaning scientists are missing something in their estimates, the researchers said. There is no missing water in the oceans, Cai said. That means the amount of water dragged down into the crust and the amount spouted back out should be about equal. The fact that they aren't suggests that there's something about how water moves through the interior of Earth that scientists don't yet understand.
"Many more studies need to be focused on this aspect," Cai said.
