On the evening of Friday 17 July at around 7:30 pm a massive tsunami swept across the sandbar that forms the outer margin of Sissano Lagoon, west Sepik, PNG. Initial media reported that the tsunami struck west of the town of Aitape in the west Sepik province, hitting at least four villages. And the wave was between 7 and10 meters and that up to 3,000 persons were killed or missing. This seemed to be an unusually damaging tsunami given the size of the earthquake (M=7). Members of the International Tsunami Survey Team decided that a field survey was necessary as soon as possible to try and determine the true value of the maximum runup and to accurately map the runup distribution along the coast. Upon arrival at the disaster relief command post in Aitape, the team was granted full access to the sealed region around Sissano Lagoon and Sissano Village, the site of the most deaths and greatest destruction.
In the past six years, the international scientific community has responded to all previous nine major tsunami disasters (Nicaragua, 1992, Flores, 1992, Okushiri, 1993, East Java, 1994, Mindoro, 1994, Kuril islands, Russia 1994, Manzanillo, 1995, Irian Jaya, Indonesia, 1996, Peru, 1996) by dispatching a team of scientists which has come to be known as the International Tsunami Survey Team (ITST for short) (refer Yeh etal.:1993, Synolakis etal.:1995, and Imamura et al.:1997). More than thirty different colleagues and more than twenty different students have participated in these surveys, from Indonesia, Korea, Japan, Mexico, Peru, Russia, United Kingdom, and the United States. In the PNG survey, we were joined by colleagues from Australia and New Zealand.
The international tsunami community have conducted many field investigations immediately after an event: e.g. Nicaragua in 1992; Flores Island, Indonesia, in 1992; Okushiri Island, Japan, in 1993; East Java, Indonesia, in 1994; Shikotan Island, Russia, in 1994; Mindoro Island, Philippines in 1994; Irian Jaya, Indonesia, in 1996; Peru in 1996. Saving lives through improved hazard mitigation is the ultimate purpose of these surveys, and these improvements can be gained only through the collection of valuable data that lead to a better understanding of the tsunami phenomena. Unfortunately, these data are highly perishable (please see the 1998 IOC Post-Tsunami Survey Guide), and the survey must be conducted within a few weeks. But our community, through long experience, is highly aware of the human tragedy and the extremely sensitive nature of a post-disaster situation shortly after the event. In all cases, we seek government approval to conduct the survey, and always conduct a post-survey briefing and provide local officials with all survey results, which are valuable in planning recovery operations and developing effective mitigation policies. We also conduct the survey with local scientists, sharing our experience with them. During each tsunami event, this process has served to increase the number of local scientists and emergency managers that actively participate in the larger tsunami hazard mitigation community.
The survey was conducted by a multinational team with representatives from Japan, the United States, Australia, and New Zealand. The team was broken up into two groups, the Japanese and everyone else. The Japanese team traveled overland from Wewak to Aitape measuring runup along the way. Japanese team members also installed seismograms in the region (Wewak, Lumi and Vanimo) to measure aftershock activity. The rest of the team traveled by ship from Wewak to the west stopping at some of the offshore islands. The two groups reunited in Aitape before a survey of the Sissano area was conducted. The boat continued west as far as Serai Village where runup values were seen to diminish considerably.