Tsunami
risk assessment
Situated
within an earthquake prone region and surrounded
by sea, Savu and Rai Jua are exposed to tsunamis
on all sides. Savu's coastline stretches 90km and
its coastal plains cover an area of approx. 30
sq.km. Thousands of people live near, or work on
the coast, such as fishermen, seaweed farmers and
salt producers. The most vulnerable communities
are the villages of Heb’a, Menia and
B’od’ae, where the coastal plains are
broadest. The
area depicted as light green on the map below
could be inundated by a large tsunami, since it
lies below the 12.5m contour.
A major tsunami could inundate
the coastal plain.
In 1977, a major
earthquake, registering 7.9 on the Richter Scale
(RS), struck 280km W/SW of Rai Jua, generating an
enormous tsunami, which claimed 180 lives on the
neighbouring islands of Sumba and Sumbawa. In
1995, an earthquake registering 6.9 RS struck
beneath the Savu Sea, midway between the island
of Alor and East Timor. The resulting tsunami
flooded an area 120m inland and caused the
disappearance of 11 people.
Earthquakes in East Nusa Tenggara
1970-2004
Enlarge
map in a separate frame
(Flash
Player required).
Since 1970, 10
earthquakes with magnitudes greater than or equal
to 6.0 RS have struck beneath the Savu Sea.
However, the Indian Ocean poses a far greater
threat, since major earthquakes are concentrated
along the plate boundary, situated 150km to the
south of Savu. This is the junction of the
colliding Australian and Eurasian Plates. Since
1900, 212 earthquakes with magnitudes greater
than or equal to 7.0 RS have occurred along this
tectonic subduction zone, which extends from
north Sumatra to east of Timor. Eighty five
percent of these quakes (183) were located
beneath the sea, with forty seven percent of
these (86 submarine quakes) generating
tsunamis-on average one every 14 months. The
proximity of their epicentres to the coast ranges
from 0 to 300 km, so the resulting tsunamis
typically hit land within 30 minutes of the
quake.
Last year's tsunami drew
the world's attention to this danger and
considerable effort is being made to ensure that,
in future, communities are forewarned of an
approaching tsunami. The Pacific Ocean has had a
tsunami warning system in place since 1965, so
the proposed Indian Ocean Tsunami Warning System
has a wealth of experience and know-how to draw
on. Such a system comprises seismological and
oceanic observation networks, feeding to regional
analysis and advisory centres, which in turn feed
to national tsunami warning centres, linked under
cooperative arrangements and coupled to national
activities in risk assessment, preparedness and
warning dissemination. Governments in the region
now recognise the need and fortunately, donors
are willing to provide the investment needed to
build the system, from the provision of
specialised instruments to the training required
to operate them.
The implementation of
the core warning system is key. However, an early
warning system also depends on sustained,
grassroots involvement. Communities will need to
understand the nature of tsunamis, how they are
likely to affect the coastal zone and how best to
respond when a warning is issued. So, education
and public awareness campaigns are being
developed to address this need. These will target
key intermediaries, such as public officials,
teachers and community leaders, who will engage
communities directly, to assess vulnerability,
test warning system operation and plan evacuation
and response strategies.
Copyright © 2007 Ina Tali/Francesca Von
Reinhaart.
© raijua.com
References:
NOAA's National
Geophysical Data Center (NGDC)
Pararas-Carayannis, G. (1977)
Indonesian Earthquake and Tsunami of August 19,
1977.
Abstracted article in Tsunami
Newsletter, Vol. X, No. 3. (Sept. 1977). (1.8MB .pdf).
International Tsunami Information Center Report.
Progress and
further requirements for the development of a
tsunami warning and mitigation system for the
Indian Ocean;
(240KB .pdf)
Second International Coordination Meeting for the
Development of a Tsunami Warning and Mitigation
System for the Indian Ocean, Grand-Baie,
Mauritius, 14-16 April 2005 IOC Information
Document No 1213, UNESCO 2005.
U.S. Government (2005)
2005 Complete
Guide to the Asian Tsunami Disaster.
U.S. Government (2005)
21st Century
Complete Guide to Tsunami Research, plus Coverage of the December
2004 Asian Tsunami Disaster (DVD-ROM).
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