過往地質事件留下的深層「傷疤」會對今日的地震造成重大影響

原文網址：www.sciencedaily.com/releases/2016/06/160610094437.htm

Deep 'scars' from ancient geological events play role in current earthquakes

過往地質事件留下的深層「傷疤」會對今日的地震造成重大影響

Super-computer modelling of Earth's crust and upper-mantle suggests that ancient geologic events may have left deep 'scars' that can come to life to play a role in earthquakes, mountain formation, and other ongoing processes on our planet.

以超級電腦對地球地殼以及上部地函做的模擬顯示，過往的地質事件可能會在這些地帶留下深遠的「傷疤」。當這些創傷再次發作就會對現今地球上發生的地震、造山運動及其他作用造成重大影響。

This changes the widespread view that only interactions at the boundaries between continent-sized tectonic plates could be responsible for such events.

這改變了廣為接受的看法中認為只有大陸尺寸的板塊在彼此之間的交界相互作用時，才會產生這些事件。

A team of researchers from the University of Toronto and the University of Aberdeen have created models indicating that former plate boundaries may stay hidden deep beneath the Earth's surface. These multi-million-year-old structures, situated at sites away from existing plate boundaries, may trigger changes in the structure and properties at the surface in the interior regions of continents.

由多倫多大學及亞伯丁大學組成的研究團隊建立的模型，指出先前的板塊邊界可以在地表深處潛伏許久。這些可以遠離現存板塊邊界長達數百萬年的構造，或許能造成陸塊內部地區的地表發生構造以及性質方面的變化。

"This is a potentially major revision to the fundamental idea of plate tectonics," says lead author Philip Heron, a postdoctoral fellow in Russell Pysklywec's research group in U of T's Department of Earth Sciences. Their paper, "Lasting mantle scars lead to perennial plate tectonics," appears in the June 10, 2016 edition of Nature Communications.

「這項研究可能使我們必須大幅重新審視板塊構造學說的中心思想。」第一作者 Philip Heron說。他是多倫多大學地球科學系 Russell Pysklywec研究團隊中的博士後研究員。他們這篇題名為「Lasting mantle scars lead to perennial plate tectonics」的論文刊登於2016年6月10日這期的《自然通訊》之上。

Heron and Pysklywec, together with University of Aberdeen geologist Randell Stephenson have even proposed a 'perennial plate tectonic map' of the Earth to help illustrate how ancient processes may have present-day implications.

Heron、Pysklywec以及亞伯丁大學的地質學家Randell Stephenson之前就已經共同提出一幅地球上「重複活動的板塊構造地圖」，幫助他們闡述過往的地質作用對現今的地質現象有何意涵。

"It's based on the familiar global tectonic map that is taught starting in elementary school," says Pysklywec, who is also chair of U of T's Department of Earth Sciences. "What our models redefine and show on the map are dormant, hidden, ancient plate boundaries that could also be enduring or "perennial" sites of past and active plate tectonic activity."

「這份地圖建立在大家都很熟悉的全球板塊構造地圖，小學入門課程中都會教到。」同時也是多倫多大學地球科學系主任的Pysklywec說。「我們的模型重新界定出那些休止、潛伏的古代板塊邊界並將它們標示在這份地圖上。它們也是過往及現今持續或『間歇』發生板塊運動的地區。」

To demonstrate the dominating effects that anomalies below the Earth's crust can have on shallow geological features, the researchers used U of T's SciNet -- home to Canada's most powerful computer and one of the most powerful in the world- to make numerical models of the crust and upper-mantle into which they could introduce these scar-like anomalies.

為了顯示地殼之下的異常地帶對淺部地質構造的主要影響，研究人員藉助了多倫多大學的SciNet，他們在此進行的數值模擬將這些傷痕似的異常構造引入地殼以及上部地函之內。SciNet是存放加拿大最強力，同時也是世上首屈一指的超級電腦的場所。

The team essentially created an evolving "virtual Earth" to explore how such geodynamic models develop under different conditions.

基本上，研究團隊創造了一顆「虛擬地球」來探討在不同的情況下這類地質動力學模型會如何發展。

"For these sorts of simulations, you need to go to a pretty high-resolution to understand what's going on beneath the surface," says Heron. "We modeled 1,500 kilometres across and 600 kilometres deep, but some parts of these structures could be just two or three kilometres wide. It is important to accurately resolve the smaller-scale stresses and strains."

「對於這類型的模擬來說，你必須要達到相當高的解析度才能了解在地表之下究竟發生了何種作用。」 Heron說。「我們可以模擬範圍寬達1500公里，深達600公里的構造，然而，這些構造當中可能有部分僅約2至3公里寬。因此要能準確解析尺度比這還要小的應力及應變是相當重要的。」

Using these models, the team found that different parts of the mantle below the Earth's crust may control the folding, breaking, or flowing of the Earth's crust within plates -- in the form of mountain-building and seismic activity -- when under compression.

利用這些模擬結果，研究團隊發現當受到壓力時，位於地殼之下的地函異常部分，可能會控制板塊內部的地殼產生褶皺、破裂與移動，並形成造山運動和地震。

In this way, the mantle structures dominate over shallower structures in the crust that had previously been seen as the main cause of such deformation within plates.

如此說來，過往認為是板塊內變形主因的淺層構造，實際上是受到地函中的構造控制。

"The mantle is like the thermal engine of the planet and the crust is an eggshell above," says Pysklywec. "We're looking at the enigmatic and largely unexplored realm in the Earth where these two regions meet."

「地函就像是地球的熱機，而地殼則是覆於其上的蛋殼。」Pysklywec說。「我們目前正在研究的是這兩個區域相交之處，是地球上充滿謎團且大多仍未被好好探討的區域。」

"Most of the really big plate tectonic activity happens on the plate boundaries, like when India rammed into Asia to create the Himalayas or how the Atlantic opened to split North America from Europe," says Heron. "But there are lots of things we couldn't explain, like seismic activity and mountain-building away from plate boundaries in continent interiors."

「真正大型的板塊構造運動多半是發生在板塊邊界，像是印度衝撞亞洲而創造喜馬拉雅山脈，或是大西洋打開使得北美從歐洲分裂出來。」Heron說。「但有很多事物是我們無法解釋的，比如在遠離板塊邊界處的大陸內部為何會有地震活動以及造山運動發生。」

The research team believes their simulations show that these mantle anomalies are generated through ancient plate tectonic processes, such as the closing of ancient oceans, and can remain hidden at sites away from normal plate boundaries until reactivation generates tectonic folding, breaking, or flowing in plate interiors.

研究團隊認為古代的板塊構造作用，像是海洋閉合，會在地函產生這些異常帶。它們可以隱藏在遠離一般板塊邊界的地方許久，直到再次活動而在板塊內部產生構造皺褶、破裂或移動作用。

"Future exploration of what lies in the mantle beneath the crust may lead to further such discoveries on how our planet works, generating a greater understanding of how the past may affect our geologic future," says Heron.

「未來對地殼之下的地函有何構造進行的探索，或許可以讓我們對地球的運作方式上有更多類似發現，並更加了解過去發生的事物會如何影響未來的地質活動。」 Heron說。

The research carries on the legacy of J. Tuzo Wilson, also a U of T scientist, and a legendary figure in geosciences who pioneered the idea of plate tectonics in the 1960's.

此篇研究傳承了 J. Tuzo Wilson。這位地質科學界的傳奇人物同樣是多倫多大學的科學家，他在1960年代便已率先倡導板塊構造學說。

"Plate tectonics is really the cornerstone of all geoscience," says Pysklywec. "Ultimately, this information could even lead to ways to help better predict how and when earthquakes happen. It's a key building block."

「板塊構造學說確實是地質科學各領域中的基石。」 Pysklywec說。「最終這些資訊甚至能讓我們更準確的預測地震會在何時及如何發生。這絕對會是至關重要的一塊拼圖。」

引用自：University of Toronto. "Deep 'scars' from ancient geological events play role in current earthquakes." ScienceDaily. ScienceDaily, 10 June 2016.