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Joint Research Centre, I-21020 Ispra (VA), Italy 
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EUROPEAN COMMISSION 
DIRECTORATE GENERAL JRC 
JOINT RESEARCH CENTRE 
Institute for the Protection and  Security of the Citizen 
Global Security and Crisis Management Unit 
CriTech 
Wednesday, 30 September 2009 
Tsunami in Samoa region 
American Samoa, 29 September 2009 
TS-2009-000209-ASM 
Flash report 
On 29/09/2009 17:48:15 UTC an earthquake of 
magnitude 8 and depth 18km triggered a tsunami with 
calculated maximum wave height of 2.2m near the 
coast of Samoa Islands Region. Media report local 
waves of up to 7m, and casualty tolls reaching 100 
deaths. 
The GDACS tsunami system, based on a tsunami 
scenario database, failed to evaluate the tsunami impact 
in real time. This was due to a hardware failure: a hard 
disk containing the scenario for this location and 
magnitude broke, and the back-up mechanism did not 
work properly. Therefore, GDACS initially estimated a 
Green alert. 
After necessary repairs alert levels were revised. The 
GDACS tsunami scenario database puts the wave height at 2.2m, raising the alert level to Orange. 
However, calculations based on exact magnitude and location show wave height of 2.9m (based on 
magnitude 8 and depth of 18km), which is a Red alert level. 
The place with highest wave heights are listed in the following table, including the time of arrival. 
The first (and highest) tsunami waves arrived after 13 minutes. The first earthquake information of 
magnitude near 8 arrived only after 20 minutes. In this case, even without hardware failures, the 
alert would have been too late for local warnings. 
 
Time 
Actual Time 
Location 
Country 
Height (m)
00:13 29/09/2009 
18:01:15 Fagamalo 
American Samoa    
2.9 
00:13 29/09/2009 
18:01:15 Mesepa  American 
Samoa  
  2.9 
00:13 29/09/2009 
18:01:15 Seetaga
American 
Samoa
2.9
00:13 29/09/2009 
18:01:15 Vaitogi 
American Samoa    
2.9 
00:13 29/09/2009 
18:01:15 Amaile 
Samoa 
 
  1.1 
00:13 29/09/2009 
18:01:15 Aasu 
American Samoa    
2.9 
00:15 29/09/2009 
18:03:27 Faleaseela Samoa
0.9
00:16 29/09/2009 
18:04:33 Afiamalu  Samoa 
 
  1.0 
00:17 29/09/2009 
18:05:39 Fuailalo 
Samoa 
 
  0.9 
00:17 29/09/2009 
18:05:39 Fasitootai  Samoa 
 
  0.9 
00:17 29/09/2009 
18:05:39 Salailua
Samoa
0.6
00:18 29/09/2009 
18:06:45 Falelima  Samoa 
 
  0.5 
 
 
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Joint Research Centre, I-21020 Ispra (VA), Italy 
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Besides the tsunami scenario database, GDACS also triggers new calculations based on precise 
location and magnitude, which become available on-line 20 minutes later. The tsunami wave 
reached the first DART buoy after 1h, after which the tsunami generation can be confirmed or 
disproved. Comparison of the results with DART ocean bottom pressure signals show a correct 
estimation of wave arrival time. 
 
Figure 1. Comparison of tsunami calculation with measurements from ocean bottom pressure buoys. 
For more information, please refer to the GDACS website:  
http://www.gdacs.org/reports.asp?eventType=EQ&ID=66388&system=asgard&location=ASM&al
ertlevel=Red&glide_no=TS-2009-000209-
ASM&TsID=1618&datetime=20090929&groupid=66356