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The TUNAMI-N2 model has been used for the purpose

of predicting surges for different earthquake scenarios.

This model uses available earthquake parameters and

assumes worst slip rate. As the model takes about 40

minutes to provide output on travel time and run-up,

a database of pre-scenarios has been created for the

entire Indian Ocean. For operational early warning, a

large spatial database (about eight terabytes) of pre-run

numerical simulations has been created that can be

accessed at the time of an earthquake event to gener-

ate a forecast of tsunami travel time and run-up

estimates for different parts of the coastline of the

Indian Ocean. The model scenarios provide informa-

tion on 1,800 forecast points which are generally towns,

cities and settlements as well as location of BPRs and

tidal stations.

Tsunami early warning centre

– A state-of-the-art early

warning centre has been established at the Indian

National Centre for Ocean Information Services

(INCOIS) with the necessary computational and

communication infrastructure that enables reception of

real-time data from all the sensors, analysis of the data

and generation and dissemination of tsunami advisories

following a standard operating procedure. A host of

communication methods have been employed for timely

dissemination of advisories. Seismic and sea-level data

are continuously monitored in the early warning centre

using a custom-built software application that generates

alarms/alerts whenever a preset threshold is crossed. The

data is organized in a central database on a storage server

and affords analysis and retrieval.

A display wall facilitates visualization of various data

streaming in, pre-run model outputs and vulnerability

maps. Tsunami warnings/alerts/watches are generated

based on preset decision support rules and disseminated

to the authorities concerned for action, following a stan-

dard operating procedure. The database is also linked

to the dedicated tsunami website through which

data/information/advisories are made available to users.

The efficiency of the end-to-end system was proved

during the large under-sea earthquake of 8.4 metres that

occurred on 12 September 2007 in the Indian Ocean.

events in the 20th century) due to the high seismic activity (75 per

cent of global activity) in the circum-Pacific belt. The Indian Ocean

Rim countries are likely to be affected by tsunamis generated in the

two known tsunamigenic zones, the Andaman-Nicobar-Sumatra

island arc and the Makran subduction zone north of the Arabian Sea

(about five per cent or less). These zones have been identified by

considering the historical tsunamis, earthquakes, their magnitudes,

location of the area relative to a fault, and tsunami modelling. In

spite of the infrequent occurrence of tsunamis (about six events

reported in the 20th century) in the Indian Ocean, they could occur

at any time and may be very devastating. The east and west coasts of

the Indian Ocean and the island regions are likely to be affected by

tsunamis generated mainly by subduction zone-related earthquakes

from the two potential source regions.

Identification and forecasting of tsunamis requires the detection of

a tsunamigenic earthquake and its parameters, generation of model

scenarios to estimate travel time and run-up height, monitoring of

sea level, a decision support system, a standard operating procedure

and mechanisms for timely delivery of information. India has

successfully set up the first tsunami warning centre in the Indian

Ocean in record time, and it has been operational from 15 October

2007.

Components of the Indian Tsunami Warning System

Sensor networks

– The Indian Tsunami Early Warning System

comprises a real-time network of seismic stations, bottom pressure

recorders (BPR) and tide gauges to detect tsunamigenic earthquakes

and to monitor tsunamis. The seismic subsystem receives real-time

seismic data from the national seismic network of the Indian

Meteorological Department (IMD) and other international seismic

networks, and is capable of detecting all earthquake events in the

Indian Ocean in less than 15 minutes of occurrence. BPRs installed

in the deep ocean are the key sensors to confirm the triggering of a

tsunami. Four BPRs in the Bay of Bengal and two in the Arabian Sea

have already been installed by the National Institute of Ocean

Technology (NIOT). Thirty coastal tidal stations have been installed

by the Survey of India (SOI) to monitor the progress of tsunami

waves.

Tsunami modelling

– One of the most important requirement for

a tsunami warning system is to generate simulations of expected

travel time (i.e. time taken by the tsunami wave to reach the partic-

ular coast) and run-up height for the tsunamigenic earthquakes.

Location

Padang

Coco’s Island

Sabang

TB3

TB10A

TB10

Port Blair

Chennai

Male

Estimates from the model scenario for 12 September 2007

Estimated Arrival Time (IST)

1751

1748

1903

1931

1930

2010

2105

2054

Estimated water level (cm)

Observed Arrival Time (IST)

1754

1748

1903

1913

1941

1945

2013

2110

2058

Observed water level (cm)

Source: INCOIS