Underwater Seismicity

Underwater Seismicity

Seismic networks are easy to install and thus commonly used for detecting earthquakes on continents.  Detecting a seismic activity is crucial for understanding the dynamics of the earth.  However, most of the earth’s surface that is 70% is covered by water. Placing seismometers on the ocean floor is difficult, and only a handful are set on specific ocean stations.

New developments show an ordinary telecommunication cable can be used to detect seismic waves when combined with top-notch frequency metrology tricks. Optical fiber cables are used as the sensing element by identifying any strains or changes of the seismic waves. An experiment was conducted where the light was sent through the optical fibers by ultra-stable lasers over terrestrial and submarine links. The real-time detection for underwater earthquakes covers a geographical distance of 25 to 18,500 kilometers from the earthquake’s epicenter.

The technology will turn intercontinental optical cables into strain sensors improving our ability to detect earthquakes. According to Barbara Romanowicz, a seismologist at California, the proposal is very lucrative. Over the years, oceanic earthquakes have gone undetected as most of the seismic stations are on land. Use of seafloor fiber networks will harness the study of the earth’s interior.

How Does It Work?

Researches use an Ultra-stable laser to inject light onto one end of the optical fiber. On the opposite end of the fiber cable, the light is monitored. In case of a seismic wave, the light traveling through the fiber will be distorted. The idea works like data transmission. A slight loss of signal means the data will be distorted and the message corrupted. By comparing the original signal from the source with the received signal at the receiver, the researchers will detect changes that determine the magnitude of the wave.

The signal will indicate where the beam was distorted, how much and for how long. Combining several measurements from multiple fiber optic cables can indicate the origin of the earthquake. The study will show where the wave started and its strength.

On September 2, 2017, Marra et al. conducted an experiment to test their earthquake detecting ability on land and sea using fiber. Vibrations were detected in a 79-kilometer cable in southern England traversing New Zealand and Japan. The magnitude of the seismic wave was 7.9 and 6.9 with other land tests indicating a magnitude of 7.3.

Another research conducted on submarine fiber-optic cable that stretches from Malta to Sicily recorded a magnitude of 3.4 in the Mediterranean. The seismometer at the Malta end was near the epicenter of the earthquake and detected the waves a few seconds before the cables, and the cables at the Sicily detected after the seismometers. The seismic detecting technique needs to be tested on further distances, but it is currently hopeful.

 Importance of Using Fiber Optic Cables to Detect 

Seismic Waves

The fiber optic cables are great for transferring digital communication between continents, diagnose cancer, monitor and maintain the gas lines among other lesser-known uses. The use of fiber optical cables to detect seismic activity will bolster tsunami detection as well. If the systems are interconnected to a tsunami station, the seismic stations can give a tsunami warning on time.

The submarine fiber optic cables that will detect earthquakes will provide insight on some of the geologic activities happening deep in the sea:

  • Ability to check the oceans activities and life in real time. The oceanographers can observe the deep abyss online without taking a yearly cruise into the sea that costs a lot of money.
  • The technology will help scientist in their research on Hawaii’s volcanoes by observing the earth’s mantle.

 

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