紐西蘭的地震學家有了驚人發現

原文網址：http://www.geologypage.com/2017/05/new-zealand-quake-scientists-discover-surprise.html

紐西蘭的地震學家有了驚人發現

紐西蘭的研究人員鑽入地震斷層深處時，他們偶然之間有了一項新發現。據表示，其可以提供給這個南太平洋國家非常大量的新能源。

科學家發現阿爾卑斯斷層中的地下水，比預期的還要熱上許多，因此或許可以用來發電，或者直接當作熱源供應給部分產業，像是酪農業者。

這項發現的驚人之處在於地熱能源通常跟火山活動有關，但科學家這次鑽探的地點並沒有火山存在。由於阿爾卑斯斷層在紐西蘭南島猶如脊柱般延伸了上百公里，因此它擁有的能源儲量可能相當可觀。

這份研究由紐西蘭威靈頓維多利亞大學的教授Rupert Sutherland主導，本周四刊登於期刊《自然》(Nature)。

Sutherland表示研究的最初目的是要在熱門觀光景點――法蘭士•約瑟夫冰川附近，取得岩芯樣品並裝設監測儀器，而非量測地下水溫，但研究人員還是對這項意料之外的發現感到十分興奮。

Sutherland在一次訪談中對美聯社表示：「它對紐西蘭的經濟價值可能相當重大。這個例子可說是前所未見。」

在他們的研究中，科學家表示他們認為熱水是由兩種作用造成。

他們說第一種作用是過往的地震將位於地球深處的高溫岩石，上推至斷層帶周遭的山脈裡面。

第二種作用是地震產生的晃動會碎裂岩石，使得雨水和融雪可以快速滲透至高溫的山脈內部，並將熱量集中於谷地下方。

Sutherland表示他們發現斷層中的水可以在地下630公尺就達到100℃的高溫。一般來說越往深處水的溫度就會越高，但在正常情況下要到地下3公里左右才能達到此溫度。

水在地表的沸點是100℃，但在地底達到此溫度水卻不會沸騰，這是因為在壓力下水能保持液態，就像是處在壓力鍋中一樣。

阿爾卑斯斷層是世上最活躍的斷層之一，它通常每300年左右就會產生一次大型地震。科學家估計在接下來的數十年內，它會再次破裂的機率達到三分之一。雖然此斷層附近沒有紐西蘭的大城市，但其產生的地震仍可能會摧毀一些小城鎮。

Sutherland表示發現高溫熱水跟預測下次地震可能襲來的時間沒有任何關聯。

他說在進行商業開採之前，科學家需要先測定熱水水量有多少、可以用在什麼地方、抽取的難易度有多高以及是否能安全利用。他說他不認為從斷層中抽出地下水會有引發地震的風險，但科學家仍然需要探討這項問題。

紐西蘭的電力已經有15%左右是來自於地熱，大多是從北島中部的陶波火山帶開採而來。Sutherland表示南島煤礦產業的縮減，可以提供探勘阿爾卑斯斷層的新地熱資源時，所需的專家意見、工程技術以及開採設備。

未參與此研究，紐西蘭奧塔哥大學的教授Dave Craw表示從全球角度來看，在此斷層中發現的高溫相當不尋常。

Craw在電子郵件中寫道：「著名的聖安地列斯斷層也有進行跟這次紐西蘭的新鑽井類似的鑽探活動，但他們遇到的溫度和地溫梯度皆遠低於阿爾卑斯斷層。對沒有活火山活動的地區來說，阿爾卑斯斷層是十分驚人的地熱異常帶。」

史丹佛大學的教授Bill Ellsworth雖然沒有直接參與此研究，但有幫忙評估研究的安全層面。他說由於液體壓力升高會弱化斷層，故此研究的發現也對了解世界各地類似斷層中，地震的形成機制有重要啟發。

New Zealand quake scientists discover surprise

When researchers in New Zealand drilled deep into an earthquake fault, they stumbled upon a discovery they say could provide a significant new energy source for the South Pacific nation.

The scientists found the water in the Alpine Fault was much hotter than expected, and could potentially be harnessed to generate electricity or provide direct heating in industries like dairy farming.

The finding was surprising because geothermal energy is usually associated with volcanic activity, but there are no volcanoes where the scientists drilled. Because the Alpine Fault stretches for hundreds of kilometers (miles) like a spine along the country’s South Island, the energy source could be enormous.

Led by Victoria University of Wellington professor Rupert Sutherland, the study was published Thursday in the journal Nature.

Sutherland said the intention of the study near the popular tourist destination of Franz Josef Glacier was to collect rock cores and install monitoring equipment rather than gauge water temperatures, but researchers are excited about their unexpected findings.

“Economically, it could be very significant for New Zealand,” Sutherland told The Associated Press in an interview. “It’s a totally new paradigm.”

In their study, the scientists say they believe two actions are creating the hot water.

First, they say, previous earthquakes have moved hot rocks up from deep within the Earth into the mountains along the fault line.

Second, the shaking has broken up the rocks, allowing rain water and snow melt to quickly percolate through the hot interior of the mountains, which concentrates the heat beneath the valleys.

Sutherland said they found the water in the fault reached 100 degrees Celsius (212 Fahrenheit) at a depth of 630 meters (2,100 feet). Water typically gets progressively hotter with depth, but under normal conditions it doesn’t reach that temperature until about 3 kilometers (2 miles) underground.

One hundred Celsius is boiling point on the Earth’s surface, although water doesn’t boil underground because it remains under pressure, much like the liquid inside a pressure cooker.

The Alpine Fault is among the most active faults in the world. It typically creates large earthquakes about once every 300 years, and scientists figure there is about a one-third chance it will rupture again in the next few decades. The resulting quake could devastate some New Zealand towns, although the fault is not located near any large cities.

Sutherland said the discovery of the hot water doesn’t have any bearing on predicting when the next quake might hit.

He said before any commercial ventures begin, scientists will need to determine the extent of the hot water, what purposes it could be used for, how easy it is to extract, and whether it can be done safely. He said he didn’t think removing water from the fault would risk triggering a quake but scientists would need to study that question as well.

New Zealand already generates about 15 percent of its electricity from geothermal sources, most of it from the Taupo volcanic zone in the central North Island. Sutherland said the declining coal mining industry in the South Island could provide needed expertise, engineering and infrastructure for any new geothermal ventures on the Alpine Fault.

He said the hot water could potentially be used by the dairy industry as a heating source to dry milk. Milk powder is one of the nation’s largest exports.

奶粉做為該國的最大出口貨物，他說熱水或許可以直接提供給酪農業作為熱源來乾燥牛乳。

Dave Craw, a professor at New Zealand’s University of Otago who was not involved in the study, said that in a global context, the high temperatures found in the fault are very unusual.

“The famous San Andreas Fault of California was drilled in a similar way to this New Zealand borehole, and the temperatures and thermal gradient encountered there were much lower than the Alpine Fault,” Craw wrote in an email. “The Alpine Fault is a spectacular thermal anomaly for an area without active volcanic activity.”

Bill Ellsworth, a professor at Stanford University who helped review safety aspects of the study but who was not involved in the research, said that because elevated fluid pressures weaken faults, the study’s findings also have important implications for understanding the workings of quakes on similar faults around the world.

原始論文：Rupert Sutherland et al., Extreme hydrothermal conditions at an active plate-bounding fault. Nature(2017). doi:10.1038/nature22355

引用自：Associated Press. ”New Zealand quake scientists discover surprise: Hot water .“ Geology Page. May 17, 2017.