How the communication cable can imagine the ground under us

With the help of IS & T employee John Morgante (right), EAPS Ph.D. Student Hillary Chan, a student, uses Mit’s existing optical fiber in -frustration as a way to imagine the ground under the campus. I have done it. Credit: Hillary Chang
When people think about optical fiber cables, it is usually about how they are used to access and access the Internet. However, optical fiber cable (glass or plastic chain that enables light transmission) can be used for another purpose. Image the ground under your feet.
Mit Earth, Atmospheric and Planetary Sciences (EAPS) PH.D. Student Hillary Chan, who recently used MIT Fiber Optic Cable Network, has used a method known as a distributed acoustic sensing (DAS) to properly imagine the ground under the campus. By using existing infrastructure, DAS has an efficient and effective method for understanding the ground composition, important factors for evaluating the dangers of local earthquakes, or risks due to damage due to earthquakes. This is a method.
“We were very wonderful from the surroundings, and we were able to extract the consistent waves and use them to get information about the basement,” explained her work co -authored with EAPS’s major research. Chang, who is the protagonist of the recent dissertation, says. Scientist nori nakata. This study is published in Landing Edge Journal.
Dark fiber
The MIT campus fiber system installed from 2000 to 2003 offers services for internal data transportation between labs and buildings, and external transportation such as campus Internet (MITNET). The campus has three major cable hubs, from which the line pops out into the building and underground, branching like a spider’s nest.
The network assigns a certain number of strands for each building. Some of them are cables that do not actively transport “dark fibers” or information. Each campus fiber hub has a redundant backbone cable, so if a failure occurs, a network transmission can switch to dark fiber without losing network services.
DAS can use existing communication cables and surrounding waves to extract information about the passing materials, which are valuable tools for cities that cannot develop conventional sensors and places such as seabed. Chang, who is studying earthquake waveforms and information that we can extract from them, decided to try it on the MIT campus.
To access the optical fiber network for experiments, Chang contacted John Morgante, a manager of an infrastructure project engineering with MIT information systems and technology (IS & T). Morgante has been involved in MIT since 1998 and has been involved in the original project of the installation of the optical fiber network, so it was able to provide personal insights on the selection of routes.
“It was interesting to hear what they were trying to achieve in the test,” Morgante says. IS & T has previously cooperated with students in various projects, including school networks, but says, “In the physical plant area, this is the first thing to remember that we actually cooperated together in experiments.” I mentioned.
They have decided a path starting from the hub of the building 24. Because it was the longest driving route that was completely underground. The wire on the ground that survived the building did not work because it was not useful in the experiment because it was not grounded. The road ran west from the east, starting with 24 buildings, and ended with a building W92 along a part of Massachusettsu Street, a part of Ammerst Street and Vasser Street.
“(Morgante) was really useful,” said Chang, explaining it as “a very good experience in cooperation with the campus IT team.”
Find the cable
After renting a interrogator, the device and volunteer groups that send laser pulse to detect the surrounding vibration along the fiber optic cable, gave a special access to connect to the hub of the building 24. 。
Chang performed a tap test to verify the route and confirm that the interrogator is working. There, I hit the ground several times with a hammer to record the accurate GPS coordinates of the cable. Conveniently, the underground route is marked by a maintenance hall cover that functions as a suitable place for testing. And she had to do it around 2 am, as she needed an environment as much as possible to collect beautiful data.
“I was hitting it next to the dormitory, and someone shouted” silently. ” Perhaps because the hammer wakes up, “Chang recalls. “I’m sorry.” Thankfully, she just tapped in several places and was able to interpose the rest of the place.
During the day, Chang and her fellow students Danger Segbefia, Concon Yuan, and Jared Brian conducted additional tests on Geopon, another device that detects seismic waves. It was a fun experience for Chang. When the data was collected in 2022, the campus escaped from pandemic measures and may still have a remote class. “Everyone was in the field and it was very good to do something by hand,” she says.
Noise around us
When Chang collected data, I was able to see a lot of environmental activities of waveforms, such as passing through cars and bicycles.
After identifying the noise source, Chang and Nakata extracted coherent surface waves from the surrounding sounds, and understood the characteristics of the ground where the cable passed by using wave speeds related to different frequencies. Hard materials will speed up speed and slower the soft material.
“I found that the MIT campus was built on a soft rock -rock soft material,” says Chang.
Such information is important for areas that are susceptible to destructive earthquakes and other earthquakes, including Massachusetts, which have recently experienced earthquakes.
The Boston and Cambridge areas, which are characterized by rapid urbanized artificial filling, are particularly dangerous because the underground structure is likely to amplify the frequency of earthquakes and damage buildings. This non -invading method for the site’s characteristic evaluation helps the building to meet the correct earthquake hazard level code.
“A destructive earthquake event will occur and need to prepare,” she says.
Details: The Lide Edge (2024), the characteristic evaluation of the city site using DAS Dark Fibers on the MIT campus in Cambridge, Massachusetz, Hilary Chang et al. Doi: 10.1190/TLE43110747.1
Provided by Massachusetts Institute of Technology
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Quotation: How to imagine the ground under us (February 4, 2025) February 4, 2025 https://phys.org/ News/Telecommunications-trecommunicati ONS Obtained from -IMAGE-Ground-beneat.html
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