Satheesh.S.C. Shenoi and T. Srinivasa Kumar

Until December 2004, not many people in India were aware of tsunami and its devastating capacity. The great Sumatra earthquake (Mw 9.3) of 26th December, 2004 generated a tsunami which exposed the vulnerability of the Indian Ocean and caused unprecedented loss of life and damage to property in the Indian Ocean rim countries. In response to this, the Government of India established the Indian Tsunami Early Warning System (ITEWS), with the warning centre operating from the Indian National Center for Ocean Information Services (INCOIS), Hyderabad, India. The Indian Tsunami Early Warning System comprises a real-time network of seismic stations, Bottom Pressure Recorders (BPR), tide gauges and 24 X 7 operational Warning Centre to detect tsunamigenic earthquakes, to monitor tsunamis and to provide timely advisories to vulnerable community. The Warning Centre is capable of issuing Tsunami bulletins in less than 10 minutes after any major earthquake in the Indian Ocean thus providing a response/lead time of about 10 – 20 minutes for near source regions and a few hours in the case of far source regions. Timely tsunami advisories (Warning/ Alert/ Watch) are disseminated to the vulnerable community using Decision Support System developed based on one of its kind Standard Operating Procedure (SOP).

The criteria for the generation of tsunami advisories (Warning/Alert/Watch) for a particular region of the coast are based on the available warning time (i.e. time taken by the tsunami wave to reach the particular coast). The Indian Warning Criteria are based on the premise that coastal areas falling within 60 minutes travel time from a tsunamigenic earthquake source need to be warned based solely on earthquake information, since enough time will not be available for confirmation of water levels from BPRs and Tide Gauges. Those coastal areas falling outside the 60 minutes travel time from a tsunamigenic earthquake source could be put under a watch status initially and upgraded to a warning, if necessary, upon confirmation of water-level data. This implies that while the possibility of false alarms is comparatively more for areas close to the earthquake source, for far source regions the rate of false alarms is very less since the warnings are issued only after confirmation of tsunami from water-level data. To reduce the rate of false alarms even in the near source regions bulletins are generated by analysing pre-run model scenarios and issued only to those coastal locations that are at risk. Based on the estimated water levels and travel times, the coastal areas are categorized into either being under Warning (Major Tsunami), Alert (Medium Tsunami), Watch (Minor Tsunami) or No Threat.

Warning Centre disseminates tsunami advisories to various stakeholders through multiple dissemination modes simultaneously (Fax, Phone, Emails, GTS and SMS etc.). Earthquake information, tsunami bulletins as well as real-time sea level observations are also made available on a dedicated website for officials, public and media. Users can also register on the website for receiving earthquake alerts and tsunami bulletins through emails and SMS. The ITEWC serves not only as a national tsunami warning centre for India, but also as a Tsunami Advisory Service Provider (TSP) for the Indian Ocean Tsunami Warning and Mitigation System (ICG/IOTWS), which is responsible for providing Tsunami advisories to all IOTWS member States.
Future work is focussed towards water level inversion, real-time inundation modelling, use of near-field GNSS measurements for real-time rupture characterisation and 3D mapping of vulnerable coastal areas.