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EARTHQUAKE AND TSUNAMI OF NOVEMBER 26, 1999 IN VANUATU

George Pararas-Carayannis
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INTRODUCTION

A 7.3 earthquake struck Vanuatu, a group of about 80 islands in the Southwest Pacific that has a population of about 190,000 people. Worst-hit was Pentecost, an island with a population of about 12,000.

This was the strongest earthquake recorded in the Vanuatu archipelago in the past 30 years. A tsunami was generated which was particularly destructive on the southern part of Pentecost.

The Pacific Tsunami Warning Center in Hawaii was correct in not issuing a Pacific-wide tsunami warning. Historically, earthquakes from this area have generated only local tsunamis. Additionally, only small tsunami wave heights were reported from stations outside the immediate area..

THE EARTHQUAKE

The large earthquake occurred shortly after midnight on Saturday morning, 26 November 1999, at 12:21 a.m. local time ( 13:21:15.43 GMT). The Strasbourg Earth Sciences Observatory in France reported the earthquake's magnitude as 7.3 on the Richter scale. The U.S. National Earthquake Information Center (NEIC) in Golden Colorado reported it as 7.1 on the Richter scale. The quake' s epicenter was at given as 16.452 South, 168.183 East, approximately 90 miles north of Port Vila. Its depth was shallow at 33km (NEIC). The quake was felt throughout the islands of Vanuatu. Numerous aftershocks of decreasing intensity continued in the days following the main event.

TECTONIC SETTING

The entire region where Vanuatu is located is characterized by high volcanic and seismic activity and is part of what is often referred to as the " Pacific Rim of Fire", an area notorious for frequent earthquakes and volcanic eruptions. This region of the Southwest Pacific Ocean is presently responsible for about ten per cent of the total energy released by earthquakes in the world.

The islands of Vanuatu are close to the New Hebrides trench, where there is active contact and interaction between the Australian and Pacific tectonic plates. The tectonic plates move at speeds averaging between 1 cm and 10 cm per year in this region. The Australian plate also shares boundaries with the Philippine Plate, the Indian Plate, the Somali Plate, the Eurasian plate and the Antarctic plate.

The 26 November 1999 earthquake occurred along a zone where tectonic plate convergence and subduction take place, as the Pacific tectonic plate submerges beneath the Australian plate. In the Vanuatu area this process of subduction has formed the New Hebrides Trench and is the cause of major earthquakes and locally destructive tsunamis.


RECENT EARTHQUAKES IN THE AREA

Since August 1998, there has been a flurry of earthquake activity in the Southwest Pacific region. The increased level of seismic activity begun on July 17, 1998 when a 7.1 undersea earthquake off the coast of Papua-New Guinea caused a huge tsunami which wiped away whole villages in the Aitape coastal area of Papua New Guinea, killing more than 3,000 people. Subsequently, NEIC has documented several large earthquakes in the New Ireland and New Britain regions, the Santa Cruz Islands and the region of Papua New Guinea, just to the north of Vanuatu.

In recent months there have been a series of other big earthquakes in the region of Papua New Guinea in the area just to the north of Vanuatu and in the region to the south. On 22 August 1999, an earthquake measuring 6.5 on the Richter scale struck the very same region of Pentecost Island. Its epicenter was located at about 200 kilometers (120 miles) south of Pentecost. On 17 November 1999 there was a 6.0 quake in Vanuatu Islands with epicenter at 5.97 South 148.81 East. On 18 November 1999 a severe earthquake with magnitude 6.9 on the Richter scale struck the New Britain region. The epicenter of this earthquake was initially determined to be 420 kilometers (252 miles) west-southwest of Rabaul, to the north of the Vanuatu Islands at 5.97 South, 148.81East. The New Britain Region, was again struck on 19 November 1999 by a magnitude 6.9 earthquake. The epicenter of this event was at 6.431 South 148.670 East.


THE TSUNAMI

Near field Effects: Shortly after midnight on Saturday morning of 26 November 1999, a destructive tsunami struck the villages of Ena and Vemagely, on the southern tip of Pentecost, an island in Vanuatu with population of about 12,000 people. The tsunami arrived in southern Pentecost island about half an hour after the earthquake.

Tsunami waves were estimated to be about 2-3 meters in height in the immediate offshore area, but these estimates have not been confirmed. The waves washed away many of the homes along the southern coast of Pentecost island and, in some areas, purportedly surged two kilometers inland.

At Vanuatu's Port Vila station, the closest to the earthquake's origin, the gauge recorded tsunami waves of 1.2 m approximately. The gauge recorded height does not represent the maximum height of the tsunami observed elsewhere in Vanuatu.

Far Field Effects: The tsunami was recorded by numerous tide gauge stations in the immediate area and throughout the Pacific, stations operated by NOAA/National Ocean Survey and the National Tidal Facility of Flinders University of South Australia.

A small tsunami was recorded further away from the source. The following tsunami heights were recorded: t Lautoka, Fiji ( Approx. 25cm); Apia - Western Samoa (Approx. 10cm); Pago Pago - American Samoa (20cm); Niue Is.(15cm); Chatham I., New Zealand (10cm); Pt. San Luis, California (10cm). At Funafuti, Tuvalu, ; Nauru, Kwajalein - Marshall Is., Papeete, Tahiti and Wake I., the recorded tsunami was less than 10cm.

In the Hawaiian Islands, the small tsunami was recorded by NOAA tide stations as follows: Hilo, Hawaii, Hawaii (10cm); Kawaihae, Hawaii, Hawaii (< 10cm); Kahului, Maui, Hawaii (20cm); Honolulu, Oahu, Hawaii (10cm) and Nawiliwili, Kauai, Hawaii (20cm).

DEATH TOLL AND DAMAGES

The earthquake and resulting tsunami caused extensive destruction, particularly on Pentecost island where a church and many houses were destroyed. Damage also occurred on the islands of Ambryn, Ape and Malacoula. The Vanuatu provinces of Penama and Malempa were declared disaster areas. Ten people died on Pentecost, two were missing and four were seriously injured by the earthquake and the tsunami. Five of the death were attributed to the earthquake and the other five when the tsunami hit. Most of the deaths occurred at the villages of Ena and Vemagely on Pentecost . About 100 people were injured, most by the earthquake. Thousands of people were left homeless and lost virtually everything in the disaster.

There was significant damage to the infrastructure of the country, as landslides blocked roads and communication to some parts in the central and southern parts of Pentecost Island. Water catchment tanks were totally destroyed.

RECURRENCE FREQUENCY - FUTURE EVENTS

The frequency of large earthquakes in this region of the southwest Pacific is not a mere coincidence. For example, one week before the Papua New Guinea earthquake in August 1998, a large quake was recorded to the west of Western Samoa, and another one occurred in Vanuatu. Given the number of large earthquakes which have been occurring in the region in the last few months, the earthquake at Vanuatu was to be expected. A quake measuring 6.5 on the Richter scale had struck the very same region three months earlier on August 22. The epicenter of this earthquake also was located about 200 kilometers (120 miles) south of Pentecost Islands. IRD (the French Research Institute for Development) had warned about an impending major quake.The present trends indicate that the seismic activity will continue in the next few months and years and that other large earthquakes and tsunamis can be expected in this region of the Southwest Pacific.

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