Lori Dingler | From deep sea cables to earthquakes and tsunamis – Times-Standard

The advantage of COVID Times is the ability to ‘attend’ meetings that used to require travel. Two months ago I listened to a Berkeley Laboratory Seismology Symposium given by Zhongwen Zhan, Associate Professor of Geophysics at Cal Tech. Zhan is at the forefront of a new breed of seismologists who are using submarine cables to collect seismic information from hitherto inaccessible areas.

This was new to me. I believed satellites were the main conduits for transmitting data in our information age. wrong. More than 95% of intercontinental communications take place over 80 million miles of cables on the sea floor. I’ve been using it while putting this column together. If you have ever used the internet, social media, or made an online purchase, you have used it as well.

Ocean cables have been in use for a lot longer than you think. The telegraph became operational in the early 19th century and groups began working on how to lay cables on the sea floor soon after. The challenges were significant – isolating conductive wires in an ocean environment and driving signals over great distances. The mid-nineteenth century saw the first successful cable between the British Isles and Europe. Transatlantic cable began operating in 1866, and India was connected to the Middle East in 1870. By 1906, cables connected North America to Japan, Hawaii, Australia, New Zealand, and other areas of Oceania.

Many of the features of these early cable systems are still present today. They were placed across the sea floor by specially adapted ships and both the ships and cables were privately owned. It was trade that drove the development and installation. Cable technology has proven immense value for business with ships able to deliver cargo and take orders to the next port in minutes instead of days or weeks. The cables were supposed to play a role in the war as well; Cutting enemy cables and protecting yourself became tactics in both world wars.

The telegraph cables of the early to mid-twentieth century faced many problems. Repeater devices have not yet been invented. Very high efforts were needed to overcome the impedance of large cable lengths that cause distorted signals. A single conductive path means that only one signal at a time can travel in any direction, limiting transmission rates to 10 to 12 words per minute. The post-WWII era saw a boom in technical innovation with repeaters and coaxial cables, providing the wider required bandwidth for a phone.

The era of modern cabling began in the 1980s with optical fibers that were able to carry information at the speed of light. Current cables are a complex bundle of six to 20 pairs of fibers, enclosed in petroleum jelly, more protective layers, stranded steel wires, and a polyethylene-coated Mylar tape. It can transmit terabytes of information every second – enough bandwidth to carry more than 100 million phone calls at the same time.

Cables are subject to natural hazards. The 1929 Grand Banks tsunami provides an example. The South Newfoundland earthquake was followed by a tsunami that reached a height of more than 30 feet. Water flooded 40 villages in southern Newfoundland and killed 28 people. Why was the tsunami so big? The earthquake that triggered the earthquake was M7.2, which is too small to explain the size of the tsunami. Submarine cables provided an important clue – they picked up 12 places right after the earthquake. Conclusion: The vibration caused a landslide along the continental slope which broke the cable. Both the earthquake and the slide contributed to the increase in the scale of the tsunami, however natural hazards are not the biggest threat to cables. Trawling accounts for 40% of submarine cable failures worldwide. The second biggest problem is installation near cable lines. Most of the cable lines are now buried in shallow waters near the coast where there is likely to be a human disturbance.

My newly discovered interest in submarine cables is their ability to provide information. Seventy percent of the planet is covered by water, and cannot be reached through direct monitoring and devices. The majority of earthquakes occur under the sea floor. Zhan’s talk introduced me to seismology with cables – new technologies where cables become tools.

Distributed Acoustic Sensing (DAS) uses dark fibers (optical fibers not used in the cable) to measure the velocity of seismic waves along the cable segment. The motion of the faults stretch or compress the length of the cable causing measurable changes in the wave velocity. The location of deflections in the cable wave provides a method for identifying earthquake foci. The disadvantage of DAS is that you need access to unused optical fibers and commercial cable owners don’t have the extra space for cables to dedicate to science.

The latest technology uses science on an optical tape that actually works. Anyone who wears Polaroid glass knows about polarization and light vibrates in one plane. The light in optical fibers is also polarized – it helps cable owners transmit multiple packets at the same time. If the cable is not disturbed, the polarization will not change from where it enters its exit. But if an earthquake does happen, the polarization will change. Zhan’s team has developed algorithms that measure changes and help restrict where an earthquake strikes.

Have you heard of the new submarine cable (“Longest Fiber Optic Line to Connect Domestically”, Times-Standard, April 1, page A2) that will connect Eureka to Singapore? Many see this as an opportunity for the Humboldt County to become a leader in internet connectivity; I think it’s a potential boon for a better understanding of our marine tectonic environment.

Most of our earthquakes are outside. What if we could find dark fibers to start gathering epicenter information, or obtain polar information to determine if a rupture occurred offshore? That might give us a few extra vital seconds for earthquake early warning and maybe even a few moments of extra time for tsunami alerts. It can also provide important information about the marine environment to oceanographers. In my opinion, it is a no-brainer. Submarine cables are here to stay, so let’s get as much useful science as possible from them.

Note: Learn more about seismology and deep-sea cables at https://news.berkeley.edu/2019/11/28/underwater-telecom-cables-make-superb-seismic-network/ and https: //www.caltech .edu / about / news / using-submarine-cables-to-detect-earthquakes.

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