Field survey on the 1998 tsunami in the northwestern area of Papua New Guinea

国际海啸调查队（ITST）于1998年7月31日至8月7日期间对巴布亚新几内亚（PNG）西北近海地震引起的海啸进行了第一次调查。7月17日星期五晚上，一场巨大的海啸席卷了构成巴布亚新几内亚西塞皮克西塞萨诺泻湖外缘的沙洲。最初的媒体报道说，海啸袭击了西塞匹克省的艾塔佩镇以西，袭击了至少四个村庄。这是7 - 10米，多达3000人死亡或失踪。考虑到地震的规模（M=7），这似乎是一次非同寻常的破坏性海啸。资讯科技科技小组成员决定必须尽快进行实地调查，以设法确定最大助高的真实值，并准确地绘制沿岸助高的分布图。对受灾地区的调查证实了报告的7 ~ 10米巨浪高度，并发现海浪最大达15米，地面水流速度达到10 ~ 15米/秒。严重的破坏和极端的海浪高度局限于Aitape和Sissano村庄之间相对较短（30公里）的海岸，特别是沿着Sissano泻湖外缘的沙洲。这表明海啸能量集中在这个狭窄的区域。虽然海啸在v型海湾、半岛、岛屿和山脊会被放大，但Sissano的海岸线是直线的，水深等高线几乎是平行的。比地震（M=7）估计的海啸更大的海啸可能不是由局部底部地形引起的，而是由海啸产生引起的。目击者看到巨大的爆炸声、热水、气泡和恶臭，表明地震引发的海上滑坡或海上天然气爆炸是海啸产生的次要机制。为了解开海啸产生的谜团，需要进一步的实地调查和研究。

The first investigation on the tsunami caused by the earthquake offshore northwestern coast of Papua New Guinea (PNG) was carried out by the International Tsunami Survey Team (ITST) during the period of 31 July to 7 August 1998. On the evening of Friday 17 July a massive tsunami swept across the sand bar 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 was 7 - 10 m 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 ITST decided that a field survey was necessary as soon as possible to try and determine the true value of the maximum run-up and to accurately map the run-up distribution along the coast. The survey to the damaged area confirmed the 7 - 10 m wave heights reported and found the place where the waves were larger up to 15 m and extreme overland flow velocities of 10 to 15 m/s. The severe damage and extreme wave heights were confined to a relatively short (30km) stretch of coast between Aitape and Sissano Villages and specially large along the sand bar the outer margin of Sissano Lagoon. These suggest that tsunami energy is concentrated in this narrow region. Although a tsunami is to be amplified in V-shaped bay, peninsula, island and ridge, the coastal line in Sissano is straight and the contour lines of water depth are almost parallel. Extremely large tsunami than estimated by an earthquake (M=7) might be caused by not a local bottom topography but a tsunami generation. Eyewitness of a loud bang, hot water, bubbles and foul smell suggest sea landslide or a gas explosion offshore triggered by the earthquake as a secondary mechanism of tsunami generation. Further field investigation and research on it are required to solve a riddle of the tsunami generation.