Internet Cable Shows the Source of Underwater Vibrations
Scientists have used Internet transmitting fiber-optic cables to overcome a long-standing geophysical difficulty: identifying where seismic sound in the ocean originates. Small vibrations of Earth called microseisms are ubiquitous. Yet, researchers have not had one way to pinpoint their sources in the ocean. An innovative use of telecom equipment has changed that.
In the research currently published in Geophysical Research Letters, Xiao et al. sent laser pulses via a commercially run fiber-optic cable linking Valencia, Spain, to Palma on the Mediterranean island of Mallorca. The researchers then measured the tiny amount of light that bounced back through the cable, a method called distributed acoustic sensing (DAS). When seismic vibrations disturbed the cable, they modified how the light returned to the source and allowed the researchers to identify the origins of microseisms.
The researchers found that the micro-vibrations emanated from source areas between a few kilometers and about ten kilometers across, but this source area migrated within a band between seven and 27 kilometres from the coast, where the sea was between 25 and 100 meters deep. Where the vibrations were most potent was not always near the source of the microseisms, nevertheless. Sometimes they were strongest in areas closer to or farther from shore.
The scientists hypothesize that this constantly shifting behavior is possible because wave-wave interactions at the ocean surface are what create microseisms, and the variable nature of local winds means that wave action also shifts.
Meanwhile, properties of the underwater environment like depth, seafloor slope, and also the seismic velocity of the subsurface framework might also influence microseisms, perhaps explaining why they were not always strongest near the source and recommending that excitation of microseisms likely differs depending on bathymetry. The authors state their results reveal the potential of DAS for understanding microseism activity.
More information:
Han Xiao et al, Locating the Precise Sources of High‐Frequency Microseisms Using Distributed Acoustic Sensing, Geophysical Research Letters (2022). DOI: 10.1029/2022GL099292 Journal information: Geophysical Research Letters
Read the original article on TOP TEK NEWS.
