Latest oceanic fiber-optic cable detects undersea quakes

Laying of a 220km fiber optic cable that will help detect earthquakes began Sunday off the south coast of Japan.

The Japan Meteorological Agency (JMA) began laying a fiber-optic cable under the Pacific Ocean on Sunday but it won't be used for telecommunications. The cable is part of an advanced monitoring and alert system that could provide warning should a destructive earthquake occur close to Japan.

Undersea earthquakes are particularly dangerous because they can start tsunami, or tidal waves -- destructive waves that possess much more energy that normal waves. Japan has been hit by killer tsunami waves in the past but the most famous series of tsunami waves are those that occurred in December 2004 following an earthquake off Indonesia. More than 225,000 people are estimated to have been killed in their wake.

The new fiber cable extends 220 kilometers off the south coast of Japan near Shizuoka prefecture -- an area that has long been viewed by seismologists as having a significant chance of a major earthquake.

Along the cable are nine large pods, each about 2 meters long and 26 centimeters wide. The pods were developed by NEC as part of the project.

In five of the pods are earthquake sensors, in three are tsunami sensors and the final one handles signal relay from the far end of the cable back to shore. From the shore the signals are sent to data processing centers in Tokyo and Osaka. The two cities are several hundred kilometers apart so should one be affected by an earthquake, the other should keep running.

Data from the pods will be used to help better determine the location and size of undersea earthquakes and the chances of a tidal wave.

Japan is one of the most seismically active nations in the world and is hit by several earthquakes per day that are strong enough to be felt. As a result it has a highly sophisticated earthquake reporting system, and typically the size and intensity of a quake is announced by the JMA and flashed over TV screens within 2 or 3 minutes of it occurring. An integral part of this reporting system is whether danger of a tsunami exists.

A more recent innovation is an early-warning system that seeks to provide notice seconds in advance of strong quakes. The system monitors the fast moving but weak primary waves to quickly determine the approximate location and intensity of a quake and attempts to get out a warning in advance of the more destructive secondary waves.

Recently the warning system provided about 13 seconds warning of a strong quake to the 1 million residents of Sendai city in northern Japan. The warning system can't yet provide alerts fast enough to those very close to the epicenter but it's still in its early days having started operation last October.

The new cable is being laid by the Subaru, a ship owned by Japanese telecom carrier NTT that is especially built for the job. It set sail from Yokohama port on Thursday last week. Before the journey reporters were allowed on-board to see how the ship works.

Cable sits in a large circular storage area that is several stories high in the center of the ship. On Thursday it contained just the 220 kilometers for the new cable system but can store up to 5,000 kilometers. Just like pulling a piece of string from the center of a ball, the cable is pulled up to the deck level of the ship and then through a series of pulleys and wheels before disappearing over the back of the boat and into the ocean.

In the deep ocean it sits on the seabed but closer to land a trench needs to be dug so it lays under the surface for protection. A simple digger sits on the back of the ship and can be dropped into the water to create the trench when required.

The Subaru will be at sea for a few weeks laying the cable.

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Martyn Williams

IDG News Service
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