SMART cables: A new undersea look at earthquakes

Thousands of seismic stations located almost entirely on land record earthquake activity around the world, but they sample the earth incompletely. This map shows earthquakes (red dots) and current or past seismic stations (green dots). The uneven distribution of seismic stations worldwide, combined with the uneven distribution of earthquakes, results in large gaps in data, particularly beneath the oceans. Los Alamos National Laboratory.

Approximately 10,000 earthquakes large enough to be felt by humans occur every year as tectonic plates below the earth’s surface slide past one another to relieve stress. The seismic activity from these earthquakes is recorded at thousands of seismic stations around the world. Using data from these stations, scientists can learn more about the geology inside of the earth, including things like earthquake location and magnitude.

Even with all those seismic stations, though, and more than 100 years of earthquake records, there are still significant holes in the data because seismic stations are not sampling the earth evenly or completely.

This happens for two reasons. First, large earthquakes do not occur uniformly across the globe. Most happen at the edges of tectonic plates, which means that scientists have more data from those areas than from areas with less seismic activity.

Second, except for a few near-shore underwater seismic stations, almost all the seismic stations in the world are on land. In other words, seismologists know much less about seismic wave behavior deep below the ocean floor. Given that oceans cover two-thirds of the planet, that’s a big gap in knowledge.

But now, that gap may be closing thanks to an international joint task force that is exploring the use of special underwater telecommunications cables to gather geophysical data.

Currently, more than 600,000 miles of underwater cables crisscross the ocean floor, but they are deaf, dumb, and blind in the sense that they carry massive amounts of data (such as financial transactions and internet) from end to end, but do little else in between.

The task force, of which Los Alamos National Laboratory is a part, is proposing the next generation of cables, called Science Monitoring and Reliable Telecommunication (SMART) cables, which would be outfitted with scientific sensors every 50 miles or so. These are primarily for oceanographic monitoring but they also include seismic sensors.

As SMART cables replace current cables, scientists will gradually have access to seismic data in thousands of new locations. More data means a better understanding of the physical properties of rocks deep inside the earth.

Los Alamos researchers are also considering how this expanded seismic coverage will improve earthquake location and size estimates, which in turn improves their ability to characterize underground nuclear tests, such as those by North Korea. Buried explosions generate seismic activity, and detecting and describing that activity is part of the Lab’s mission under the National Nuclear Security Administration’s Ground-Based Nuclear Detonation Detection program.

More seismic data will likely also increase researchers’ ability to estimate seismic hazards—essentially the probability of an earthquake in a given location and how extreme the resulting damage to human life and infrastructure might be. Because earthquakes can trigger tsunamis, tsunami hazards can also be assessed.

First, researchers must demo a prototype of the SMART cables before this technology can really start making waves. Then scientists will start filling in the holes with data from the watery part of the world.

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Charlotte Rowe works in the Earth and Environmental Sciences Division at Los Alamos National Laboratory, where she supports the Ground-based Nuclear Detonation Detection team. She holds degrees from New Mexico Tech and the University of Alaska-Fairbanks.