FACTBOX: How the Indian Ocean gets tsunami warnings

LONDON (Reuters) - For more than 40 years, the Pacific Tsunami Warning Center (PTWC) has been alerting countries in the Pacific region to the dangers of killer waves.

Following the 2004 Indian Ocean tsunami that killed almost 230,000 people, the United Nation's Intergovernmental Oceanographic Commission (IOC) began coordinating efforts to create an Indian Ocean tsunami early warning system.

Before 2004, there were no sea-level monitoring instruments in the Indian Ocean and many countries did not have agencies responsible for tsunami warnings or points of contact to receive messages from international warning centers.

Five years on, a vast network of seismographic centers, national warning centers or agencies, coastal and deep-ocean stations is in place across the Indian Ocean to detect potential tsunamis and pass on warnings to communities.

Here's how the system works:

WARNING CENTRES

When an earthquake strikes in the Indian Ocean region, data from a variety of sources is transmitted to the Pacific Tsunami Warning Center (PTWC) based in Hawaii and the Japan Meteorological Agency (JMA) in Tokyo.

The two centers currently have responsibility for providing the Indian Ocean with what are known as tsunami "watches."

By 2011, a number of so-called Regional Tsunami Watch Providers (RTWPs) in Indian Ocean countries are set to take over this function. Australia, India, Indonesia, Malaysia and the Asian Disaster Preparedness Center in Bangkok are on track to become regional watch providers.

Countries able to invest more in technology will share data with smaller states that cannot, such as the Maldives or the Seychelles.

In addition, the ADPC has been coordinating its own efforts since 2005 to have a multi-hazard early warning system, known as the Regional Integrated Multi-Hazard Early Warning System

(RIMES).

RIMES will work alongside the national and regional watch providers and will also share information with Hawaii and Japan. RIMES is expected to be operable early next year.

Hawaii and Japan receive earthquake information and data from tidal gauges and Deep-ocean Assessment and Reporting of Tsunamis (DART) sensors or buoys.

They also receive news bulletins, telegrams, and information over the telephone. The Commission for the Nuclear-Test Ban Treaty Organization (CTBTO) also contributes data from seismographic stations.

The centers locate and determine the size of earthquakes, determine whether they have the potential to produce tsunamis and predict tsunami wave arrival times wherever possible.

It takes about 15 to 20 minutes for earthquake data to be deciphered and a tsunami watch to be issued.

SENDING TO THE COUNTRIES

The two centers issue watches, if necessary, to national bodies in the Indian Ocean and it is the responsibility of each national agency to alert its population, by whatever means.

Many national agencies will have also received their own information, from local or regional seismic centers, buoys, news bulletins and so on, and all this information will be fed back and forth between Hawaii, Japan and the region.

WARNING THE POPULATION

Warnings to the population are delivered over the airwaves -- radio, television, SMS, email -- and manually, using bells, megaphones or loud-speakers attached to mosques.

In some countries, well-rehearsed drills will kick in and local agencies will coordinate an evacuation.

On the ground in many Indian Ocean nations, NGOs and community groups are involved in educating and coordinating local populations to know what to do when they hear a tsunami warning or when they feel or see signs of an earthquake or tsunami - when the earth shakes or the sea recedes.

Technology does not reach all areas and even if it does, warnings can be confused or not in the right language for all the affected people to understand. In other areas, there are no escape routes as transport infrastructure is poor.

(Reporting by Katherine Baldwin; Editing by Jerry Norton)