Detecting future disasters

New underwater seismic sensors will be able to warn of the next ‘Big One’

Imagine having an early detection system to warn when volcanic eruptions, earthquakes and tsunamis were about to happen. That’s exactly what Charlotte Rowe, a seismologist at the Los Alamos National Laboratory, is grappling with.

Rowe is a research scientist, and serves on the International Joint Task Force for SMART— Science Monitoring And Reliable Telecommunication — Cables.

“Right now, almost all of our seismographs are on land, and the oceans cover 75 percent of the planet. So there’s a huge part of the globe where we don’t have any sensors,” said Rowe.

A CT scan of the earth

A computed tomographic scan — otherwise known as a CAT scan — is a medical imaging technique used in radiology to produce detailed images of the body for diagnostic purposes.

“We can do that to the earth as well,” said Rowe during ‘The Sounds Under the Sea’ online presentation Monday (May 17), part of the Science on Tap series coordinated by LANL’s Bradbury Science Museum.

“We have a lot of seismometers located around the planet. And if you have lots of sources and lots of receivers, you can shoot rays through the earth,” she said.

Most of the seismometers are located on land, where it’s easiest to install them. But earthquakes occur most frequently at the plate boundaries, and many of those are under the ocean, where there are very few seismometers.

Ocean bottom seismographs

To help improve data collection under the ocean, the National Science Foundation started a program called Ocean Bottom Seismic Instrumentation Pool (OBSIP), which loans ocean bottom seismographs, or OBSs, to researchers.

“First of all, it only lasts a year or two at most. So you can’t use it for regular monitoring of earthquakes,” said Rowe. “Second of all, it’s extremely expensive to put these instruments out and then retrieve them.”

“Because communicating under the water is so difficult, they store all their data onboard,” she said. “You don’t get the data until two years later, when you go out and you haul that instrument back on your ship and you download it. So there are limitations for our purposes of just how useful these could be.”

SMART cables

According to Rowe, there are over a million kilometers of transoceanic telecommunication cables in existence today. Deployed by ships, the fiber optic cables lie on the ocean floor and connect to terminals on shore, sending data back and forth between continents.

“But that’s all they do. They’re deaf, dumb and blind. So they can’t help us at all — yet. Say hello to Science Monitoring And Reliable Telecommunications, or SMART cables,” said Rowe.

The cables are a new initiative by the International Joint Task Force, and would add seismic sensors to new transoceanic telecommunication cables whenever they get replaced. Cables have a lifespan of 10-20 years.

The miniaturized sensors would be placed about every 75 kilometers in the SMART cable’s repeaters, designed to boost the signal as data travels through the cable — sometimes thousands of kilometers.

“The key to everything is these repeaters,” said Rowe, who added that sensors could also monitor water pressure and temperature, and transmit data back to terminals on shore.

“If we were to replace all of these cables, which eventually will happen as time marches on, and have sensors in all the repeaters, we would have something like 20,000 additional seismic sensors crossing the ocean floors,” said Rowe.

Rowe said the SMART cables would support climate studies, ocean circulation, sea-level monitoring and global geophysical modeling. They would also provide tsunami and earthquake monitoring and early warning, which would help disaster risk reduction.

“The Joint Task Force has got buy-in from UNESCO, so it’s part of the United Nations supporting it,” said Rowe. “We’ve got buy-in from a number of governments around the world. They’re very interested in this because it can help them to sense disturbances that are happening that could impact their people.”

“It’s a very exciting new frontier in seismology, as well as climate science and oceanography,” said Rowe.

The SMART cables would support climate studies, ocean circulation, sealevel monitoring and global geophysical modeling.