2005 Sumatran earthquake

The 2005 Sumatran earthquake occurred at 16:09:37 UTC (11:09:37 p.m. local time) on March 28, 2005. The hypocenter was located at , 30 km (18.6 miles) below the surface of the Indian Ocean, where subduction is forcing the Indo-Australian Plate to the south-west under the Eurasian plate Sunda edge. The area is 200 km west of Sibolga, Sumatra, or 1400 km northwest of Jakarta, roughly halfway between the islands of Nias and Simeulue. Seismic recordings give the earthquake a magnitude of about 8.7, and effects were felt as far away as Bangkok, Thailand, a distance of 1000 km [1].

Contents

1 Summary and impact

2 Aftershock magnitudes

3 Tsunami risk

4 Humanitarian response

5 External links

Summary and impact

The quake, possibly a heavy aftershock from the 2004 Indian Ocean earthquake, lasted for about two minutes in total, longer than most of the aftershocks felt to date. The recent quake was so large it has had its own aftershocks, with almost a dozen temblors measuring 5.7 or larger recorded in the region soon after the first one. At 8.7, this is the second largest earthquake in the world since 1964; only the December 26, 2004 earthquake was stronger. A debate has arisen among seismologists over whether this should be considered an aftershock or a "triggered earthquake" as it was larger than typical aftershocks and on a different fault.

The earthquake was felt across the island of Sumatra, and caused widespread power outages in the Indonesian city of Banda Aceh, already devastated by the December 2004 tsunami, and prompted thousands to flee their homes and seek higher ground [2]. In the Malaysian capital of Kuala Lumpur (and surrounding townships such as Bandar Sunway in Subang Jaya) high-rise buildings were evacuated.

On the Indonesian island of Nias, off the coast of Sumatra, hundreds of buildings have reportedly been levelled by the earthquake, with dozens possibly trapped in the rubble and 330 people reported dead. Media reports indicate that estimated death toll is at least 1000 people with 220 dying in the largest town, Gunungsitoli. Nearly half of Gunungsitoli's population (27,000) have fled the town. The control tower at the nearby airport (Banaka ) has collapsed and relief flights will be operating out of Sibolga on nearby Sumatra. Shortly after the quake, Indonesian Vice-President Jusuf Kalla announced that initial damage reports suggest that the ultimate death toll on Nias may reach between 1,000 and 2,000 [3].

Although many governments were concerned about the threat of a tsunami, and evacuations were carried out in coastal regions of Thailand, Malaysia, and Sri Lanka, no major tsunamis have been reported.

Aftershock magnitudes

So far there have been eight major aftershocks in the region, measuring 6.0, 6.7, 5.5, 5.8, 5.7, 5.7, 5.5, and 5.8, respectively. This currently covers the period between the earthquake itself and the next morning (March 29, 2005).

Tsunami risk

Tsunami warnings were issued by the US National Oceanic and Atmospheric Administration (NOAA) [4] and by the Thai government. The Pacific Tsunami Warning Center released an information bulletin about 20 minutes after the earthquake stating that there is no anticipated threat to Pacific coastlines, but warning of the possibility of destructive tsunamis on waters near the earthquake's origin. Experts from the PTWC announced shortly after the earthquake that they expected any tsunami effects to be directed primarily south of the quake's epicentre [5].

The Australian Broadcasting Corporation reported on the first day from an Indonesian military source that a 3 m-high wave hit Simeulue Island, "causing extensive damage shortly after a massive earthquake" [6]. On 30/31 March, ABC Radio carried first-hand reports from two Australians who had been on or near Nias. Marcus Keeshan, who has lived in these island for about 7 years as a surfing tourism operator, had been in a tourist boat at anchor between Simeulue Island and the Banyak Islands late on Monday night when the earthquake struck. He reported the boat shaking for about a minute then, from about 20 minutes later there were alternating surges that caused the boat to drag its anchor, "rushing, like, with an incredible force, probably 10 or 15 knots of current moving in one direction. The boat was dragging anchor, the current moved 180-degree swing. And then it happened again, the third time the current changed. It rushed for, what? ... 20 minutes it'd rush for.... Like, big waves. It was like we were motoring along.... and in between the change it would go calm for a short period, just totally, yeah, for maybe a minute or two, or five minutes, completely calm, dead calm" [7].

Portions of Thailand's southern coast were evacuated as a precaution, and NOAA advised an evacuation of 600 miles of coastline in Sumatra. Evacuations also occurred in the northern Malaysian states of Penang and Kedah, as well as the eastern coast of Sri Lanka. Many of the southern states of India were also put on high alert; all of these areas had seen significant damage from December's tsunami.

By about three hours after the initial shock, no significant tsunami activity had yet been reported in the vicinity of Sumatra, which would be the first area to be struck by any such activity. The Pacific Tsunami Warning Center had announced, in its final bulletin, "when no major waves are observed for two hours after the estimated time of arrival or damaging waves have not occurred for at least two hours then local authorities can assume that the threat is passed" [8]. Although tsunami warning systems had been actively discussed since the December 2004 earthquake, none had yet been implemented in the Indian Ocean, and so no data was available directly from the Indian Ocean.

After the detection of minor tsunami effects south of the epicenter, including a 30 cm tsunami on Australia's Cocos Islands, the island states of Mauritius, Madagascar, and the Seychelles in the South Indian Ocean issued warnings to their populations soon afterwards. These warnings, too, proved to be false alarms, and were withdrawn early on the day following the earthquake.

Humanitarian response

The United Nations talked with the Indonesian government to take further actions to prevent a possible catastrophe after the strong earthquake, and the US State Department has announced that it will help countries affected by a possible tsunami.

Australia announced it would provide AUD 1 million in emergency aid, and, at the request of the Indonesian Government, dispatch Australian Defence Force medical teams and equipment to Nias [9]. The Australian naval ship HMAS Kanimbla, having only recently left Aceh, was redeployed to the region from Singapore. At about 0930UTC 2 April 2005, one of Kanimbla's two Sea King helicopters (callsign: Shark 02) crashed on the island of Nias while taking medical personnel to a village. Nine personnel were killed; six were Navy , plus three from the Royal Australian Air Force. Two others were recovered alive from the site by the other Sea King and given medical assistance in Kanimbla's hospital facilities. This tragedy unfolded just a day before a state visit by Indonesian President Susilo Bambang Yudhoyono to Australia, which meant that he and the Prime Minister of Australia, John Howard, were able to express mutual sorry for their coutries' losses.

The Indian government announced aid of USD 2 million for the earthquake victims [10].

External links

Wikinews has a news story related to this article:

Panic in Sumatra after new earthquake

BBC News: Panic in Sumatra after April 10th magnitude 6.7 earthquake about 120km (75 miles) south-west of the city of Padang - also see Wikinews