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Standard operating procedure at the early warning centre
–
The criteria for generation of different types of advisories
(warning/alert/watch) for a particular region of the coast are based
on travel time. The warning criteria are based on the premise that
coastal areas falling within 60 minutes travel time from a tsunami-
genic 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 have been put under a watch
status and upgraded to a warning only upon confirmation of water-
level data. For example, if a tsunamigenic earthquake happens on
the coast of northern Indonesia, parts of the Andaman and Nicober
Islands falling within 60 minutes travel time of a tsunami wave will
be put under warning status. Other areas will be put under watch
status and upgraded to a warning only if the BPRs or tide gauges
reveal significant change in water level. This implies that the possi-
bility of false alarms is higher for areas close to the earthquake source;
however, the issue of false alarms does not arise for other regions
since the warnings are issued only after confirmation of water-level
data.
To reduce the rate of false alarms even in the near source regions,
alerts are generated by analysing the pre-run model scenarios, so
that warnings are issued only to those coastal locations that are at
risk. Within the tsunami warning areas, based on the estimated water
levels and directivity maps, the coastal areas will be categorized under
different risk zones, as Major Tsunami, Medium Tsunami and Minor
Tsunami.
Vulnerability maps
– Tsunamis and cyclonic storms result in gener-
ation of waves of different period and height that are termed ‘surges’.
These wave parameters depend on earthquake source parameters,
(in the case of tsunami), bathymetry, beach profile, coastal land
topography and presence of coastal structures. These surges cause
flooding of seawater into the land as much as one kilometre or more,
resulting in loss of human life and damage to property. To minimize
such losses, it is imperative to prepare coastal vulnerability maps
indicating the areas likely to be affected due to flooding and rending
damage.
The TUNAMI-N2 model has been used for the purpose of
predicting surges for different scenarios of earthquakes and to indi-
cate the extent of inundation of seawater into the land.
This information has been used for taking precaution-
ary and mitigation measures such as the evacuation of
people, avoiding human settlements and large invest-
ment, and designing appropriate structures in
risk-prone areas. Information from remote sensing and
field investigations is being integrated into GIS for
modelling and mapping of inundation of seawater for
determination of setback lines, planning coastal
defences, and so on.
Case study: 12 September 2007
INCOIS generated a database of model scenarios
considering various earthquake parameters. The pre-
run scenario for the 12 September 2007 event was used
to calculate the estimated travel time and run-up
heights at various coastal locations and water level
sensors (tide gauges and BPRs). The directivity map
generated from the selected scenarios showed that the
south-east and south-west Indian coast was likely to be
affected by a minor tsunami (~20cm), as were the
Andaman and Nicober Islands (~10cm) which is
evident from the observations of tidal stations at
Chennai and Portblair.
The estimates from the model scenario matched well
with the observations from BPRs and tidal stations. The
end-to-end system performed extremely well enabling
reception, display and analysis of the real-time and
model data sets as well as generation and dissemination
of timely and accurate advisories following the standard
operating procedure. An estimate of the errors for the
initial estimate of earthquake parameters and the run-up
was used to provide necessary advisories to the author-
ities concerned, thus avoiding unnecessary public
evacuation for this event.
Contribution to the Indian Ocean region
The Indian tsunami early warning centre is equipped
with world-class computational, communication and
technical support facilities and is considered the most
modern tsunami warning centre in the world at the
time of writing. The instrumentation of the Indian
system is established in such a way that it is capable
of detecting tsunamis originating from both known
tsunamigenic sources in the Indian Ocean. It has
robust application software based on geospatial tech-
nologies to generate and disseminate timely tsunami
advisories to the Indian Ocean countries. INCOIS has
also set up the warning centre infrastructure so as to
have the capabilities of a regional tsunami watch
provider. India has begun providing regional tsunami
watch services from its national system for the Indian
Ocean region. At present, it provides earthquake
source information to give potential tsunami threat
and travel times. Shortly, earthquake parameters, travel
time, run-up height and potential threat zones will be
provided. The warning centre can also support the
generation of inundation maps and risk and hazard
assessments.
Parameters
Elapsed time from earthquake
information issuance (distant)
Accuracy of earthquake hypocentre
location
Accuracy of earthquake hypocentre
depth
Accuracy Earthquake Mw magnitude
Accuracy of the tsunami forecast
amplitude/height
Performance
Target
15 min.
30 km
25 km
0.2
Factor of 2
Performance
Achieved
13 min.
20 km
5 km
0.1
~ 25 %
Estimated errors for the initial estimate of earthquake
parameters and run-up, 12 September 2007
Source: INCOIS