New Zealand scientists learn lessons from Samoa tsunami

NIWA www.scoop.co.nz 4 Dec 09;

Preliminary results from their survey of the physical and human effects of the Samoa tsunami have direct relevance for New Zealand say the scientists involved.

A team of NZ scientists say the results of their field work after the Samoa Tsunami are of interest internationally and here in New Zealand.

The team from the National Institute of Water & Atmospheric Research (NIWA) and GNS Science spent nearly two weeks in the field: six days in American Samoa and seven days in Samoa. In Samoa, the NIWA / GNS Science delegation was part of a UNESCO–IOC International Tsunami Survey Team.

This project was unique in that it involved a coordinated team of international scientists who sought to collect evidence across a wide spectrum of the tsunami’s impact on communities, individuals, infrastructure, and the environment.

“We broke new ground for the disaster loss assessment research community. Our results illustrate an effective use of cutting edge field methods,” says NIWA’s Dr Shona van Zijll de Jong.

The aim of the visit was to gather a wide range of information to help Samoa, and other Pacific Islands including New Zealand, become better prepared to cope with future disasters.

Samoa, like New Zealand, is vulnerable to a wide range of natural disasters such as earthquakes and tsunamis, cyclones and floods. Samoa’s recent experience with natural disasters, such as the two closely-spaced cyclones in 1990 and 1991, have assisted in better preparing many local communities to withstand the impact of such natural hazards and to plan for the future.

Preliminary results from their survey of the physical and human effects of the Samoa tsunami have direct relevance for New Zealand say the scientists involved.

Size of tsunami

The Samoa tsunami consisted of two to three significant waves; the second wave was said by witnesses to be larger. The delay between the earthquake and the arrival of the first wave was about 10 minutes in Samoa and 20 minutes in American Samoa.

The maximum height reached by the tsunami on the land was 14 metres above mean sea level in Samoa and 10 metres in American Samoa. The furthest inland the waves reached was over 700 metres from the shore.

“This size of tsunami is also possible for New Zealand, equivalent to about a one-in-500 year event for the most populated parts of New Zealand,” says GNS Science spokesman John Callan.

Building damage

Buildings sustained varying degrees of damage. The importance of reinforcement was very clear – traditional light timber buildings were typically completely destroyed at an inundation depth of 1.5m or higher, whereas adding minimal reinforced-concrete columns reduced the damage levels significantly.

Building damage was correlated with water depth, structural strength, shielding, condition of foundations, quality of building materials used, quality of workmanship, and adherence to the building code.

It was also very clear that plants, trees, and mangroves reduced flow speeds and depths over land – leading to greater chances of human survival and lower levels of building damage.

“The same thing will be true in New Zealand as in Samoa: solidly constructed buildings which are appropriately located will survive much better than flimsy buildings right on the beach,” says Dr Stefan Reese of NIWA.

“It’s also clear that practices such as flattening sand dunes or removing beach vegetation would increase the potential for tsunami damage.”

Community response

In Samoa, it was clear that community-based tsunami education activities had saved lives in some areas, while in others there was still some confusion about how to respond.

The impact of the tsunami may have permanently changed residential patterns in Samoa. “Many people are scared of the sea, and people are staying away from devastated villages” says Dr van Zijll de Jong.

“The sea has been a source of livelihood and identity for generations. The violence of the tsunami really shook them. Their sense of personal security and economic well-being is deeply shaken.”

The Government of Samoa is very supportive of communities that want to resettle further inland. However, the families that have moved inland are very aware of the challenges facing them in re establishing their communities, particularly with it now being cyclone season. There is a very strong social fabric in Samoa, through families, villages, religious organisations and right up into government at a local and national level. It is this strong social fabric that strengthens the local, cultural and economic features of the Samoan coastal communities and holds the basis for the resilience that allows people to more quickly recover from disasters says van Zijll de Jong.

The team also found that national and international response to the disaster had been extremely good. The interface between the Government of Samoa and in-coming international, regional and local humanitarian groups who had the capacity to respond to the disaster was impressive.

The team from NIWA and GNS Science was part of a UNESCO-IOC International Tsunami Survey team from New Zealand, Australia, Fiji, French-Polynesia, Italy, Japan, and the USA, in collaboration with teams from several ministries within the Government of Samoa.

The research report and methods are of interest to the local and international disaster loss assessment research community: New Zealand Ministry of Civil Defence and Emergency Management; the World Bank; United Nations Development Programme and Intergovernmental Oceanographic Commission (IOC) of UNESCO (United Nations Educational, Scientific and Cultural Organization)

Samoan Tsunami wave was 46 feet high
Yahoo News 4 Dec 09;

WELLINGTON, New Zealand – The tsunami that killed more than 200 people in the Samoan islands and Tonga earlier this year towered up to 46 feet (14 meters) high — more then twice as tall as most of the buildings it slammed into, scientists said Friday.

New Zealand scientists studying the size, power and reach of the tsunami as part of efforts to guard against future disasters said they found up to three destructive waves were caused by the magnitude 8.0 undersea earthquake in September.

The massive waves that struck Samoa, American Samoa and Tonga totally destroyed traditional wooden buildings, many of them singly story, along the coast while reinforced concrete buildings sustained only minor damage, said Stefan Reese, a risk engineer with New Zealand's National Institute of Water and Atmospheric Research.

The waves were up to 46 feet (14 meters) high, Reese told The Associated Press. The scientists measured watermarks on buildings and trees to help confirm the height of the waves.

"In some areas there was virtually nothing left" after the waves reached up to 765 yards (700 meters) inland, Reese said.

Wide reefs saved some villages by helping to reduce the waves' height to about 10 feet (3 meters), Reese said.

The Samoan quake created a sea floor fault up to 190 miles (300 kilometers) long and 23 feet (7 meters) deep.

The Sept. 29 tsunami killed 34 people in American Samoa, 183 in Samoa and nine in Tonga.