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Savu & Rai Jua News - May '05

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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