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Tuesday, June 15, 1999 Published at 15:34 GMT 16:34 UK


Seafloor observatories to monitor earthquakes

The Joides Resolution is one of the few ships capable of the job

By BBC News Online Science Editor Dr David Whitehouse

For the first time, automated, long-term observatories are to be established on the sea floor in one of the world's most active earthquake zones.

Their measurements could help forecast future earthquakes.

An array of sensors will be placed down deep boreholes about 150 kilometres off the east coast of Japan. The region is known as the Japan Trench. The sensors will record earthquakes as well as the slow collision between two of the Earth's plates.

Bump and grind

At the site, the Pacific Plate is colliding with and sliding under the Eurasian Plate, a process called subduction.

Subduction zones are the sites of the largest and most destructive earthquakes on the planet. These are caused by the sudden release of built-up stress as one plate grinds past the other.

Japan is particularly vulnerable to frequent and damaging earthquakes because it sits on the so-called "Ring of Fire", a ring of volcanoes and earthquakes that surround the Pacific Ocean.

Monitoring seismic activity over an extended period of time will enable scientists to understand better how and when strain is released at the Japan Trench. The data may help scientists to forecast earthquakes more accurately.

Deep down

The Joides Resolution, the world's largest research ship, will drill the holes.

[ image: The boreholes will drill 1,000 metres into the sea floor]
The boreholes will drill 1,000 metres into the sea floor
Scientists hope to establish the long-term geophysical observatories in the bottom of two boreholes. The holes will be drilled approximately one kilometre into the ocean floor, under more than two kilometres of water.

Each observatory will contain a strain-meter, two seismometers, a tilt-meter, and a temperature sensor.

Initially both observatories will have replaceable data recording devices and batteries. They will periodically be serviced by remote-controlled submarines similar to those used to explore the Titanic.

Eventually real time power supply and data retrieval will be possible when the observatories are connected to nearby fibre-optic cables.

Two drill sites have been carefully selected near the plate boundary. The first located in a region with frequent moderate-sized earthquakes and the second in a region that is geologically much quieter.

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