地球每26秒脈動一次已60年，科學家追蹤到非洲某處依然無解
2020-11-01
地球正在有節律地脈動，每26秒一次，這是科學家在1960年代初發現的。然而60年過去了，雖然經過很多科學家的努力，已經將引發脈動的地方定位到很小的區域——非洲西海岸畿內亞灣的邦尼灣，引發脈動的原因依然撲朔迷離，沒有確切的解釋。
最早記錄這種脈動的，是一位名叫傑克·奧利弗（Jack Oliver）的研究人員，1960年代他在哥倫比亞大學的拉蒙特-多爾蒂地球觀測所工作。那時還沒有數字地震儀，奧利弗在紙質記錄中發現，在「南部或赤道大西洋」的某個地方，出現了這種周期性的震動，在北半球的夏季（南半球的冬季）表現更強烈。
美國地質調查局地質學家加里·霍爾科姆（Gary Holcomb）在1980年更仔細地觀察了這種奇怪的微地震後，發現它在暴風雨中最強；2005年，科羅拉多博爾德大學實驗室的格雷格·本森（Greg Bensen）在排除了儀器問題和分析錯誤後，將這個強烈的震動信號定位到了非洲西海岸的畿內亞灣。
到了2011年，聖路易斯華盛頓大學地震學家道格·維恩斯（Doug Wiens）實驗室的研究生加勒特·歐拉（Garrett Euler）終於確認，這種震動來自畿內亞灣的邦尼灣。在2013年發表的論文中，他的解釋是，海浪在海洋中傳播時，雖然水壓差可能不會對海床產生太大影響，但當它撞擊大陸架時，會導致海床變形，並產生地震脈衝，就像敲桌子會在桌面其它地方感受到震動一樣。
不過2013年也發表了另一篇論文，中科院測地所武漢大地測量國家野外科學觀測研究站一個研究小組認為，這種26秒的周期性脈衝信號，最有可能來自靠近邦尼灣的聖多美島（SãoTomé）的一座火山，日本的阿蘇火山也曾經引發過這種微地震。
然而科學家們對這兩個解釋都持懷疑態度，全球很多地方的海浪都會撞擊大陸架，世界各地也有很多火山，為什麼只有邦尼灣的海浪火山會引發這種持續60年，每26秒就震動一次的脈衝信號呢？邦尼灣的海浪、大陸架或火山有什麼特別之處嗎？
研究仍在進行，科學家們希望藉助這次新冠肺炎病毒在全球爆發，更多人都隔離在家的安靜時期，更仔細地檢查世界各地的地震儀，從中發現更多的信號，徹底解開地球每26秒就脈動一次的神秘原因。
Earth keeps pulsating every 26 seconds and no one knows why
Oct 31, 2020
Why is Earth pulsating every 26 seconds, and why can’t scientists explain it after 60 years? This is an enigma wrapped in a periodically predictable mystery motion.
It could be a harmonic phenomenon, a regular seismic chirp caused by the sun’s energy, or a beacon drawing scientists to its source to begin a treasure hunt.
When was this Earth pulse first discovered?
In the early 1960s, a geologist named Jack Oliver first documented the pulse, also known as a “microseism,” according to Discover. Oliver, who worked at Columbia University’s Lamont-Doherty Geological Observatory at the time, heard the noise, but didn’t have the advanced instruments seismologists have now at his disposal.
Since then, scientists have spent a lot of time listening to the pulse and even finding out where it comes from: “a part of the Gulf of Guinea called the Bight of Bonny,” Discover says.
What is Earth’s pulse?
1. waves crashing on continental shelf?
Earth’s pulse is a mystery. Some researchers think the pulse has a kind of prosaic cause. Under the world’s oceans, the continental shelf acts as a gigantic wave break — it’s the boundary off the very far edge of, for example, the North American continental mass where the highest part of the plate finally falls off into the deep abyssal plain.
Scientists have theorized that as waves hit this specific place on the continental shelf in the Gulf of Guinea, this regular pulse is produced.
If that sounds improbable, consider all the different shapes of drums, from timpani to bass drums to bongos that you hit with your hands. It’s not impossible that just one shape of continental shelf “drum” would create the right harmonic bang to rattle the Earth. If that’s true, we’re probably lucky it’s just one.
Here’s an article corroborating this hypothesis:
https://strangesounds.org/2014/10/humming-sounds-earth-breathing-sounds.html
2. A volcano?
But other researchers think the cause is a volcano that’s also very near the critical spot: “That’s because the pulse’s origin point is suspiciously close to a volcano on the island of São Tomé in the Bight of Bonny,” Discover explains. And there’s a similar volcanic microseism that’s already well documented in Japan.
Well it really seems the Earth is breathing. Look at the gifs in the article below.
https://strangesounds.org/2013/07/our-earth-is-breathing-and-her-heart-is-beating.html
It seems like reams of new scientific research emerge every day, but the mystery pulse is a good reminder that so much remains to be discovered. Scientists have studied the pulse and debate its origin, but it just hasn’t reached a tipping point of interest to be solved.
Discover explains that researchers have likely been studying higher-priority seismic events instead, which makes sense.
This year, for example, seismologists have an important opportunity to study a much quieter Earth during global quarantine. That could mean they all redouble efforts on high-priority subjects, or it could mean that the right listener at the right time could finally understand the 26-second chirp once and for all. In a perfect world, we could have both.
http://strangesounds.org/2020/10/earth-pulse-mystery-geology.html
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