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EARTHQUAKES—“CAN YOU HEAR ME NOW?”

WHAT WITH the Earth’s surface being three-quarters water, oceanic research is essential to understanding our world. However, such monitoring is especially difficult to deploy and maintain. Science magazine, published weekly by the American Association for the Advancement of Science, recently reported on innovative ways to accomplish this. Here are tidbits gleaned from Science, February 26, 2021, and from previous gleanings here at SimanaitisSays, also based on a Science article.

Undersea Seismic Monitoring. As noted here at SimanaitisSays earlier this month in “Finned Seismologists Aid in Oceanic Research,” scientists recognized that fin whale chirps—among the loudest communications in the animal kingdom—could be used to monitor undersea seismic activity. Sonic waves generated by these chirps prove as usable to oceanic studies as more expensive means generated by conventional technology.

In Science, February 26, 2021, William Wilcock writes of another innovative approach to oceanic monitoring: “Illuminating Tremors in the Deep: Telecommunications cables on the seafloor monitor seismic activity.”

A Ring of Fire of tectonic discontinuities extend around the world; so does a network of submarine telecommunication cables. Recent research is using the cables to monitor the Ring of Fire. This and the following image from Science, February 26, 2021.

Details are given in Science, February 26, 2021, in “Optical Polarization-based Seismic and Water Wave Sensing on Transoceanic Cables,” by Zhongwen Zhan, et al. As described in Brent Grocholski’s Research news item in the same issue, the technique can be likened to “waiting for earthquakes to call,” an analogy to “listening to whale chirps.” 

Using the Curie Telecommunication Cable. In their Abstract, Zhan and his research colleagues write, “We successfully sensed seismic and water waves over a 10,000-kilometer-long submarine cable connecting Los Angeles, California, and Valparaiso, Chile, by monitoring the polarization of regular optical telecommunication channels.”

The researchers continue, “We detected multiple moderate-to-large earthquakes along the cable in the 10-millihertz to 5-hertz band. We also recorded pressure signals from ocean swells in the primary microseism band, implying the potential for tsunami sensing.”

“The Curie cable (red curve),” researchers describe, “is a 10,000-km-long submarine fiber-optic cable connecting Los Angeles (LA) and Valparaiso (VAP) along or across a series of active plate boundaries (blue and orange barbed lines). More than 50 earthquakes with a magnitude of >7.5 (blue dots) have occurred in this region since 1900.”

Measuring Quakes. “During our initial test period of SOP [State of Polarization] sensing (December 2019 to September 2020), we detected ~20 moderate-to-large earthquakes (yellow stars labeled with date and earthquake magnitude), most of which occurred in the Central and South American subduction zones. JTS and SLBS (purple triangles) are coastal seismic stations along the Curie cable.” 

Conclusions. Zhan and his associates say, “Our method, because it does not require specialized equipment, laser sources, or dedicated fibers, is highly scalable for converting global submarine cables into continuous real-time earthquake and tsunami observatories.” 

All that’s required, in a sense, is listening for earthquakes to say, “Can you hear me now?” ds 

 © Dennis Simanaitis, SimanaitisSays.com, 2021 

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