1998 Papua New Guinea Tsunami


Introduction
July 17th, 1998 was a devastating night in the South Pacific for Papua New Guinea (PNG).Villages along the shore as well as inland villages/towns lost homes and lives due to an earthquake that was followed quickly, within minutes, by three enormous waves (tsunami). The actual cause/source of the tsunami is debatable and still being researched by scientists. International assistance was rapidly taken into account, nineteen countries were able to donate money, supplies and provide relief for the victims. Many suggest the event to be the most disastrous tsunami of the entire century. New Guinea is known for its seismic activity, its known as an arc-continent collision which means that plates are sliding past each other causing stress. New Guinea's tectonic boundaries are very different from all other countries.

Earthquake
On the evening of July 17th, 1998 at 8:49.15.33 UTC an Earthquake of a magnitude 7.1 hit the North Central Coast of Papua New Guinea, (south of Indonesia and north of Australia) about 45 Miles Southeast of Vanimo. The National Earthquake Information Service (NEIS) shows that the epicenter was about 12 miles offshore in the Pacific and the hypo-center was quite shallow only 6 km in depth, see Figure 1.0. The mechanism of earthquake is classified as steeping reverse faulting of The North Bismark Plate, which is sub-ducting below the Australian plate. The length of the actual fault fracture is approximately 30 km long. Figure 1.1 shows the actual movement along the fault and shows the hypo-center of the earthquake. Previous earthquakes in the same area show a variety in types of faulting like normal faulting and strike slip faults. For instance,the north area near the Australian Plate and The North Bismark Plate has very complicated seismic activity with other smaller plates. The Caroline plate sub trusts under the Australian Plate,which causes many strike slip movements. Studies have shown that there was an earthquake on July 4th, which had a magnitude of 5.5, 13 days prior to the magnitude 7.1. The initial earthquake would not be considered a fore-shock, because it did not occur within 24 hours of the "main-shock." The map below shows the location of the actual earthquake, refer to figure 1.0.
external image basemap.gifFigure 1.0 (http://walrus.wr.usgs.gov/tsunami/images/basemap.gif)
external image tsu98PNGChicagoTribune.jpg Figure 1.1 (http://www.drgeorgepc.com/tsu98PNGChicagoTribune.jpg)
Undersea Landslide
Since many scientists argued that a earthquake of a magnitude 7.1 could not create a tsunami, under water research was conducted. After studying the bathymetry of the ocean floor before and after the tsunami, scientists found that the actual cause of the tsunami was not the earthquake alone.The earthquake is responsible for triggering an undersea mudslide, where a huge undersea slump of sediment is liable for the three massive waves that struck Papua New Guinea. Scientists discovered this sediment slump by using a mult-beam echo sounding equipment. It showed a semi-circular slope of debris, which concluded that an undersea cliff had collapsed. This new research tool is currently explaining other tsunami events that were before blamed by fault and plate seismic activity, like the Santa Barbara tsunami of 1812.
Tsunami
Even now the direct cause of the tsunami is still quiet controversial. Initially, the earthquake caused the seafloor to drop downward and then it elasticized back upward causing a upward push of the water. Despite such arguments about the earthquake and the landslide, three enormous waves sweep through the region of Aitape and Sissano Village, minutes after the actually earthquake. Interestingly the first wave struck twenty minutes after the actual earthquake/landslide, below shows the actual movement of the waves, refer to Figure 1.2.
external image leadoff.gif
Figure 1.2 (http://walrus.wr.usgs.gov/tsunami/images/leadoff.gif)
Many scientists were quite surprised by this event, most did not believe that a tsunami could occur due to a magnitude 7.1 earthquake and that is why the undersea landslide is relevant. The tsunami produced waves that were between 7-10 meters high that quickly crashed the coast. The waves traveled 40 kilometers inland, which was relatively short in distance with comparison to the actual size of the waves.The bathymetry of the seafloor explains why a tsunami of such great height could have occurred. The northern coast of Papua New Guinea has an extremely linear and steep slope so the water near the shore is not shallow, refer to figure 1.3.The black dots represent the seismic location of the earthquake according to the university's research.
external image png_small.gif Figure 1.3 (http://walrus.wr.usgs.gov/tsunami/images/png_small.gif


Consequences
Unfortunately three villages were destroyed. Sissano Lagoon, Warapu and Arop experience much chaos and devastation. Children were grasped by the waves and taken into the sea, as well as men and women. After the third wave, not one house was left standing. A total of 2,182 people died as a result of the earthquake and of the tsunami, and over 1,000 were hurt. Statistics show that most of the injuries and lives taken were of children. The Sissano village completely disappeared. Homes were damaged, 10,000 people were homeless and forced to relocate elsewhere. All buildings and structures 400-500 meters of the shoreline were destroyed. Dislocated victims were forced to move to a new location inland, and it has been hard for many to adapt to this new region. Inland, it is hotter and the region is more humid, therefore there are many insects and water is more scarce, compared to living on the shoreline. Figure 1.4 shows the shoreline and the water residing inland. This event was considered the most disastrous tsunami of the century.
external image 42_841.jpg Figure 1.4 (http://www.ngdc.noaa.gov/hazard/icons/small_res/42/42_841.jpg)

Relief/Mitigation
The initial response from other countries to the disaster was delayed 16 hours due to communication issues. After the issues were resolved help proceeded immediately. Nineteen countries replied to the disaster, supplying victims with first aid, rebuilding materials and money. Supplies and money donated was equivalent to 6 million U.S. dollars. The three major villages of Sissano Lagoon, Warapu and Arop were completely destroyed, the people that were displaced were forced to rebuild new villages farther inland. Closure of fishing harbors majorly affected the food resources for roughly a year, until remodeling and rebuilding was complete. It took two years for schools, water irrigation, roads and sanitation systems to be newly reconstructed. Dislocated survivors were given new equipment and tools to engineer new homes and canoes for themselves.
Conclusion
The Papua New Guinea tsunami of 1998 is one of the most recognized natural disasters of the century. The newly discovered recognition of the undersea landslide has up roared many scientists. Other scientists are quite fascinated with this discovery and are starting to use mult-beam echo sounding equipment to observe the seafloor of previous tsunami areas. The PNG tsunami resulted from both the earthquake and the undersea landslide, one triggered another like a domino effect. As of today, 12 years later scientists are still studying the north shore of PNG. Survivors are still coping with the consequences of lost loved ones and trying to adapt to the climate of their new villages. Thankfully much support was aided to the victims and hopefully a new warning system will assure that this type of Natural Disaster will not result the way it did in 1998.

References:
Mitigation Lessons from the July 17, 1998 New Guinea Tsunami WEB 4 Mar, 2010 <http://cat.inist.fr/?aModele=afficheN&cpsidt=15120559>
USGS WEB 15 Feb, 2010 <http://walrus.wr.usgs.gov/tsunami/PNG.html>
USGS WEB 14 Feb 2010 <http://earthquake.usgs.gov/regional/neic/>
National Geophysical Data Center WEB 16 Feb, 2010 <http://www.ngdc.noaa.gov/nndc/struts>
The Sissano, Papua New Guinea tsunami of July 1998 - offshore evidence on the source mechanism, DR. Tappin, Watts P,Volume 175, Number 1, 15 May 2001 , pp. 1-23(23) WEB 16 Feb 2010 <http://www.ingentaconnect.com/content/els/00253227/2001/000001/art00131>
Relief Web, WEB 16 Feb 2010 <http://www.reliefweb.int/rw/dbc.nsf/doc108?OpenForm&rc=5&emid=WV-1998-0220-PNG>
"Tsunamis and Earthquakes - 1998 Papua New Guinea Tsunami Descriptive Model - USGS WCMG." Home Page - USGS Western Coastal and Marine Geology. Web. 18 Mar. 2010. <http://walrus.wr.usgs.gov/tsunami/PNG.html>.