科学家利用光纤电缆发现海底断层
Scientists Spot an Undersea Fault Using Fiber-Optic Cables
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2019-12-03 00:38
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火星译客

Working from a beachside shack on California's Monterey Bay, Nate Lindsey fired a stream of infrared laser pulses down a long fiber-optic cable extending onto the ocean floor. The miles-long cable had been there for a decade, transmitting data to and from scientific instruments on the seafloor, but Lindsey, a geoscientist at UC Berkeley, was trying something new. He and his team had disconnected the cable from all its usual sensors so they could use the fiber itself to sense vibrations on the ocean floor.

内特-林赛在加利福尼亚州蒙特雷湾的一个海滨小屋里工作,他向延伸到海底的一根长长的光纤电缆发射了艺术红外激光脉冲。这条长达数英里的电缆已经在海底存在了十年,用于向海底的科学仪器传输数据,但是加州大学伯克利分校的地球科学家林赛正在尝试一些新的东西。他和他的团队已经切断了电缆与所有传感器的链连接,这样他们就可以利用纤维本身来感知海底的震动。

By monitoring how light beamed and bounced through the transparent fiber, Lindsey’s team was able to describe the texture and topography of the earth it was buried in. As they report in the journal Science today, the method led them to discover a new underwater fault 5 miles from the Monterey Bay coastline. The technique could potentially help monitor and characterize swaths of unmapped ocean floor, using the so-called dark fiber that telecom companies have already buried across oceans but do not actively use.

通过检测光线在透明光纤的传播和反射情况,林赛的研究小组能够描述埋藏在底下的土壤的结构和地形。正如他们今天在,《科学》杂志上报道的那样,这种方法是他们在距离蒙特蕾湾海岸线5英里的地方发现了一个新的水下断层。这项技术可能有助于监测和描述尚未绘制地图的大片海底,使用的是电信公司已经在大洋彼岸埋藏但并未积极使用的所谓暗光纤。

“To my knowledge, this is the first example of this technique used under the sea,” says geoscientist Philippe Jousset of the GFZ German Research Centre for Geosciences, who has used fiber to sense earthquakes and volcanic activity on land. “And with it, they could observe phenomena we were not aware of before.”

“据我所知,这是这项技术在海底使用的第一个例子,”GFZ德国地球科学研究中心的地球科学家飞利浦-乔赛特说,他曾利用光纤来感知地震和陆地上的火山活动。“有了它,他们可以观察到我们以前不知道的现象。

Called distributed acoustic sensing, this technique is a sharp departure from how earth scientists typically monitor the ocean floor. Conventional underwater seismometers, which can cost $100,000 apiece, sense vibrations only at a single location. Lindsey says that a 12-mile stretch of fiber-optic cable served the role of 10,000 conventional instruments. So exploiting existing, unused fiber networks could be a practical strategy for mapping the ocean floor. Jousset, for example, has already collaborated with Icelandic and Italian telecom companies to use their fiber to measure seismic activity on land.

这种被称为分布式声波传感技术,与地球科学家通监测海底的方法截然不同。传统的水下地震检波器,每台价值10万美元,只能在一个地点检测振动。林赛说,一段12英里长的光纤电缆承担了10000台传统仪器的使用。因此,利用现有的、未使用的光纤网络可能是绘制海底地图的一个实用策略。例如,乔赛特已经与冰岛和意大利的电信公司合作,利用他们的光纤来测量陆地上的地震活动。

To find the fault off Monterey Bay, Lindsey’s team spent four days in 2018 sending light pulses down the fiber, the same way it would transmit data. Most of the light travels straight through the clear, hair-thin stretch of glass. But because no fiber is perfectly transparent, some tiny amount of light will always scatter, bouncing back toward shore off microscopic flaws in the glass. From his shack onshore, Lindsey could detect this reflected light. If the earth surrounding some part of the fiber is stretched or compressed in any way—perhaps by an earthquake—the character of the reflected light changes. By timing how long it took the pulse to fire, bounce off the impurity, and return to shore, Lindsey could locate where the disturbance occurred.

为了找出蒙特雷湾的故障,林赛的研究小组在2018年花了四天时间沿着光纤发送光脉冲与光纤传输数据的方式相同。大部分光线直接穿过透明的、像头发丝一样薄的玻璃。但是因为没有一种光纤是完全透明的,一些微小的光总会散射开来,反射回玻璃上的微小瑕疵。从陆上的的小屋里,林赛可以探测到反射的光线。如果环绕纤维某部分的土壤以任何方式被拉伸或压缩——也许是由于地震——反射光的特性就会改变。通过计算脉冲发射,从杂质反弹,回到岸上的时间,Lindsey可以找到扰动发生的地方。

During their four-day experiment, a small earthquake rumbled about 30 miles away. The vibrations shook the earth near the fiber, and Lindsey’s team then mapped how the seismic waves moved through the area. From their analysis, they inferred the presence of an unexpected crack in the ocean floor: a new fault.

在他们为期四天的实验中,30英里外发生了一次小地震。这种振动使纤维附近的地面发生震动,林赛的研究小组随后绘制了地震波如何让穿过这一地区的地图。根据他们的分析,他们推断出海底出现了一个意向不到的裂缝:一个新的断层。

By mapping new faults, fiber cables could fill a much needed gap in scientists’ knowledge of the oceans. Less than 20 percent of the world’s earthquake sensors are in the oceans, even though they make up 70 percent of Earth’s surface area. More detailed maps will help scientists make more accurate predictions about earthquakes and tsunamis. “Locating small faults gives us more knowledge of the bigger faults and where the potential hazards could be,” says Jousset.

通过绘制新的断层图,光纤电缆可以填补科学家对海洋知识继续的空白。尽管海洋占地球表面积的70%,但全世界只有不到20%的地震传感器位于海中。更详细的地图将帮助科学家们对地震和海啸做出更准确的预测。”定位小断层可以让我们更好的了解更大的断层,以及潜在的危险在哪里,“朱塞特说。

One outstanding challenge is that fiber sensors produce massive quantities of data. Lindsey’s team collected 4 terabytes in this experiment, and scaling up to the entire ocean would generate an untenable amount of data. Some researchers have begun to investigate methods for compressing the data with machine learning, says Jousset.

一个突如其来的挑战是光纤传感器产生大量的数据。林赛的团队在这个实验中手机了4tb的数据,放大到整个海洋,将产生一个难以维持的数据量。一些研究人员已经开始研究用机器学习压缩数据的方法。

Still, Lindsey thinks the technology is mature enough to become a worldwide utility over the next decade. “There are really high hazard areas where this would be a great monitoring tool,” he says, citing locations off the coasts of Taiwan, India, and the western US, where telecom cables are already buried. That fiber could watch for earthquakes while you Netflix and chill.

尽管如此,林赛认为这项技术已经足够成熟,可以在未来十年成为全球公用事业,”在一些高危险地区,这将是一个很好的监测工具,"他表示。他指的是台湾、印度和美国西北部海岸的一些地方,电信电缆已经埋在那里。这种纤维可以用来观察地震,而你只需要在线观看和冷却。

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