12 years on, India's tsunami alert system a reliable tool

It was early in the morning on December 26, 2004, and no one had any clue how the world was going to change within the next few hours. Just before 8 am, the entire South Asia was shaken by an earthquake of magnitude 9.3 that originated off Indonesia, releasing an amount of energy equivalent to 23,000 atom bombs that fell upon Hiroshima.

The world’s second largest earthquake triggered a devastating tsunami causing unprecedented loss of life and damage to property in the Indian Ocean rim countries. It was considered one of the deadliest natural hazards in history, killing over 2,30,000 people in 14 countries. In India, it claimed 10,749 lives, according to official estimates.

Once the aftershocks faded away, a group of scientists and policymakers put their heads together to figure out what could be India’s response in case of a recurrence. One of the things they decided was to create a tsunami alert system. Before 2004, there was no tsunami warning system in the Indian Ocean. In the absence of real-time monitoring of earthquakes or a network to monitor the sea level, there was no alert for the monstrous waves that swept Indonesia, Thailand, Sri Lanka and Indian coastal states like Kerala, Tamil Nadu, Andhra Pradesh, Puducherry and the Andaman and Nicobar Islands.

“Three days after the tsunami, it was decided that an early warning system be set up by India,” said geologist Harsh Gupta, who was then secretary of the Department of Ocean Development. He prepared a detailed plan, which was approved by the Planning Commission and the Prime Minister’s Office. Other scientific departments extended their support and 30 months from the day of the approval, the Indian tsunami warning system was up and running at the Indian National Centre for Ocean Information Services (INCOIS), Hyderabad.

The system comprises a real-time network of seismic stations, a chain of seven bottom pressure recorders, tide gauges and a round-the-clock operational tsunami warning centre to detect tsunamigenic quakes, monitor the waves and provide timely advisories.

As part of the Indian tsunami early warning system, a real-time seismic monitoring network has been established by India Meteorological Department (IMD). It consists of 17 broadband seismic field stations transmitting data through V-SAT communication to the central receiving stations located at IMD headquarters in Delhi and INCOIS, Hyderabad, simultaneously for processing and interpretation. In addition, data from around 300 global seismic stations is received at INCOIS. These datasets help determine the epicentre of a quake and its and magnitude.

To determine an earthquake’s potential to trigger a tsunami, the magnitude value is essential. All earthquakes of value more than 5 on the Richter Scale are auto-located within 5–10 minutes of occurrence.

To confirm whether an earthquake has actually triggered a tsunami, it is essential to measure the change in water level near the fault zone with high accuracy. This is done by using two basic types of sea level gauges — coastal tide gauges and open ocean buoys.

INCOIS has installed a network of 31 tide-gauge stations along the coastline. The institute also receives data from 300 international stations. While tide gauges that initially detect tsunami waves provide little advance warning to people at the actual location of the instrument, they can give residents of the coasts where the waves have not reached yet, an indication of the tsunami, its speed, and its approximate strength.

However, what lies at the core of the alert system are bottom pressure recorders that are used to detect the sea level changes near to the tsunamigenic regions and consequent propagation of the waves in the open ocean. Initially, they were imported but now the National Institute of Ocean Technology (NIOT), Chennai, has begun to develop them in-house.

Buoy system network
As part of the tsunami early warning system, a network of tsunami buoy systems has been established by the INCOIS and NIOT. The network comprises seven tsunami buoys — only six are operational at the moment — installed in the Indian Ocean transmitting data through satellite links to INCOIS. Each of them is placed in such a way as to provide sufficient warning time and redundancy in case of a tsunami originating at the Java-Sumatra region or the Makran coast off Pakistan.

From historical studies, it is clear that all earthquakes in tsunamigenic source regions do not trigger tsunamis. “To know whether the earthquake has actually triggered a tsunami or not, it is essential to measure the change in water level in the open ocean with high accuracy in real time. Our biggest advantage is that we don’t issue false warnings unlike the Pacific system,” says Gupta.

Since October 2007, the National Tsunami Early Warning Centre at INCOIS has been issuing accurate tsunami advisories for all under-sea earthquakes of greater than or equal to 6.5 in the Richter Scale. The warning system has been undergoing constant improvements incorporating the latest developments in tsunami science and information and communication technology.

On successful implementation of regional tsunami services, in 2011, the Indian Tsunami Early Warning System was designated as the regional tsunami service provider entrusting with it the responsibility og providing tsunami advisories to Indian Ocean rim countries. As part of this service, New Delhi now carries out communication tests and conducts mock tsunami alert drill.

“We are now improving upon the model to predict how much water ingress can happen in case of a tsunami. This would also help us create storm surge maps for coastal India,” said M Rajeevan, Secretary, Ministry of Earth Sciences. What was Department of Ocean Development in the past has now been transformed into the Ministry of Earth Sciences. It has led to the creation of a storm surge map between Cuddalore and Machhlipatnam in Tamil Nadu.