Darwin and Sumatra rocked by offshore earthquakes

Monday, November 21, 2005 

An offshore earthquake shook buildings in Darwin in Australia's Northern Territory today, and an earthquake with a magnitude of at least 6.2 struck off the coast of Sumatra yesterday, triggering a tsunami alert.

Geoscience Australia says the offshore quake registered 5.3 on the Richter scale. No damage has been reported in the city of Darwin or the community of Port Keats which is the nearest town to the quake's epicentre in a region known for its moderate seismicity. The quake's epicentre was located 500 kilometres west-north-west of Darwin in the Banda Sea. The earthquake hit at 9.51am (CDT).

Geoscience Australia (the government's geological organisation) says the region may be unstable for a few days and aftershocks or another quake may be felt. Duty seismologist, Dr Svetan Sinadinovski, says it was a shallow quake and the subterranean make-up of the area allowed the tremor waves to travel to Darwin without losing much energy. He says the quake was on Australia's continental shelf, which is a common place for seismic activity.

"That is the area where Australian plate collides with Asian plate and that extends through the Indonesian islands up to Sumatra and Thailand in the north and east through PNG to Tonga and New Zealand," he said. "Preliminary reports point to a 5 to 6 in the Darwin region - this means that the earthquake would have been felt by almost everyone indoors according to the Modified Mercali Scale which measures the impact of seismic waves on structures."

"People would have felt this earthquake up to 500km away from the epicentre, and we have heard numerous reports of residents in the Darwin area having felt the effects of the event," he said.

Among those who felt the quake were participants involved in the trial of Bradley John Murdoch in the Northern Territory Supreme Court in Darwin - where chairs and TVs shook in the court building.

The Bureau of Meteorology's Darwin office was also shaken, but no reports of damage have been received by police.

"We felt it - I felt the building sway and some of the monitors shook a little," the bureau's duty forecaster, Billy Lynch, said. "We are on the third floor of a three-story building."

Sumatra Earthquake

An earthquake with a magnitude of at least 6.2 struck off the coast of Sumatra yesterday, triggering a tsunami alert, officials said. There were no immediate reports of a tsunami, damages or casualties. The quake's epicenter was located off Simeulue, 160 miles southwest of Medan on Sumatra's northwest coast, according to the U.S. Geological Survey(USGS).

Indonesia's Meteorology and Geophysics Agency put the quake's magnitude at 6.2, whilst the USGS said the magnitude was 6.5. The quake rocked nearby Nias island and was felt in Medan, said an official from the Indonesian agency's Jakarta office.

Simeulue island is near the epicenter of the December 26 quake that caused a massive tsunami. The Pacific Tsunami Warning Center in Hawaii said there was no threat of a tsunami to Pacific coastlines, but quakes of this size can sometimes generate local tsunamis along coasts near the epicenter.

Sumatra has been affected by strong aftershocks since the 2004 Indian Ocean earthquake. Experts say the fault line is unstable and may produce another massive quake soon.

Other earthquakes

The biggest earthquake to strike the region, in 1998, had a magnitude of 6.9. The largest earthquake ever recorded was in Chile in 1960. This magnitude 9.5 earthquake resulted in the death of 5,000 people. In 1976 a smaller 8.0 earthquake in China caused the death of an estimated 255,000 people. More recently, in December 2003 an earthquake in Iran resulted in the death of approximately 50,000 people.

Geoscience Australia said the 5.3 quake did not generate a tsunami. The 2004 Indian Ocean earthquake, which had a magnitude of 9.0, triggered a series of lethal tsunamis on December 26, 2004 that killed over 270,000 people, making it the deadliest tsunami in recorded history.

In March 2005 another strong earthquake rocked parts of Darwin, with tremors lasting several minutes felt across the city and rural areas. The quake measured 7.2 on the Richter scale, and its epicentre was 500 kilometres east north-east of East Timor in the Banda Sea.

Sources

• "Offshore earthquake shakes Darwin" — News Limited, November 21, 2005

• "Earthquake rattles Darwin" — Australian Broadcasting Corporation, November 21, 2005

• "Quake shakes northern Australian city" — DILIGENT MEDIA CORPORATION, November 21, 2005

• "Image: Recent Earthquake - Banda Sea" — Geoscience Australia, November 21, 2005

• "Recent earthquakes Measured by Geoscience Australia" — Geoscience Australia, November 21, 2005

• "Large earthquake felt in Darwin - Media Release" — Geoscience Australia, November 21, 2005

• "Geoscience Australia - Earthquakes Factsheet" — Geoscience Australia, June 24, 2004

• "Earthquake shakes Darwin" — ABC, March 2, 2005

• "Preliminary Earthquake Report - SIMEULUE" — U.S. Geological Survey, National Earthquake Information Center, November 19, 2005

• "Earthquake strikes off Indonesia" — BBC Online, November 20, 2005

• "TSUNAMI BULLETIN NUMBER 001" — PACIFIC TSUNAMI WARNING CENTER/NOAA/NWS, November 19, 2005