New Delhi/Hyderabad, Oct. 15: Six water pressure sensors placed on the seabed in the southern Bay of Bengal and northern Arabian Sea will act as sentinels in India’s tsunami early warning system, which was formally inaugurated today.

The sensors — four in the Bay and two in the Arabian Sea — will look for changes in ocean water level and send readings via satellite to the Indian National Centre for Ocean Information Services (INCOIS) in Hyderabad, the hub for the system.

The Rs 125-crore early warning system will also use a network of seismic stations, tide gauges and computer simulations based on seabed studies to issue alerts about tsunamis — waves sometimes triggered by undersea earthquakes.

The Hyderabad centre receives real-time data from a network of national and international seismic stations, and can detect all earthquakes of magnitude 6 or greater in the Indian Ocean region within 20 minutes.

“The (sea) bottom pressure sensors will allow quantitative monitoring of ocean water level,” said Prem Shankar Goel, secretary in the department of earth sciences.

In the event of an earthquake that generates tsunami waves, the Hyderabad centre will analyse the data it gets from the seismic stations, tide gauges and pressure sensors to issue an alert to the Union home ministry for dissemination to susceptible areas.

The efficiency of the end-to-end system was proven during the 8.4-magnitude earthquake that occurred in the Indian Ocean on September 12, Goel said. But in the coming months, six more pressure sensors will be added to the system.

An earthquake along the Andaman-Nicobar-Sumatra arc could send a tsunami rolling towards the east coast and the Andaman and Nicobar Islands, while an undersea quake in the northern Arabian Sea could threaten the west coast with a tsunami.

After the December 26, 2004, tsunami that had killed an estimated 230,000 people in South and Southeast Asia, including some 18,000 in India, the department of science and technology had pledged an early warning system before October 2007.

Inaugurating it, science and technology minister Kapil Sibal today said the system had been established without any time or cost overruns.

However, from their current positions, the six pressure sensors are unlikely to be of use to the southern part of the Nicobar archipelago, which is close to the zone of possible tsunami-generating earthquakes near the northeastern tip of Sumatra.

“For areas that lie very close to sites of undersea earthquakes, where a tsunami could reach within 30 minutes, we can’t wait for data from the pressure sensors. We will use alternative mechanisms to issue alerts,” a senior INCOIS scientist said.

Data about earthquake location and magnitude will be used to issue rapid alerts -- within minutes of an earthquake, the scientist said.

When the September 12 earthquake occurred, an alert was sent to Nicobar much before data from the pressure sensors could be analysed.