Last update: 29 March 2005;14:05 Paris time

28 March 2005, 23:09 local time: Magnitude 8.7 earthquake occurs near Sumatra. Newsreports indicate at least 290 people killed, 100 injured and 300 houses destroyed on Nias and extensive damage on Simeulue. The earthquake was felt in Indonesia, Malaysia, Singapore and as far north as Bangkok, Thailand. The Island of Nias off Sumatra was the hardest hit. No tsunami damage was reported.

Press coverage: (quotes - click on link to see full articles on source sites)

• BBC News : ".Hundreds of people are believed to have died in Indonesia after a massive earthquake that triggered tsunami alerts around the Indian Ocean...no tsunami materialised on this occasion as a much smaller area of the ocean floor moved, seismologists say."
• CNN: "Initial assessments by U.N. and Red Cross teams from two islands off the western coast of Indonesia indicate Monday's quake will not be nearly as devastating as the December 26 quake. ... But no tsunamis were reported along Indonesia's island coasts, and India, Thailand and Malaysia canceled previously issued tsunami warnings early Tuesday"
• Reuters : "More than 1,000 people are feared to have died in a massive earthquake that hit a small island off western Indonesia overnight, but panic across Asia that it would trigger another devastating tsunami quickly receded.
• Antara news (Indonesia) : http://www.antara.co.id/en/seenws/?id=2222
• MCOT.org: http://etna.mcot.net/query.php?nid=37172
  

Other information sources

• WAPMERR: Real-Time Estimate of Losses Due to Strong Motions After the Sumatra Earthquake of 26 December 2004

The following information is now available:

• Tsunami information bulletins issued by PTWC

• Sea level observations for 28 March 2005

• Preliminary earthquake report by USGS

• Travel time model results

• Peak wave height model results

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NEWS ON THE EVENT

Paris, 29 March 2005: 14:05: Initial information indicates that the earthquake generated mostly horizontal movement which explains that the tsunami effects were minor. The USGS published the following "Preliminary Earthquake Report " (U.S. Geological Survey, National Earthquake Information Center , World Data Center for Seismology, Denver , http://earthquake.usgs.gov/recenteqsww/Quakes/usweax.htm )

The earthquake of March 28, 2005 occurred principally on the interface of the Australia plate and Sunda plate and was caused by the release of stresses that develop as the Australia plate subducts beneath the overriding Sunda plate. The Australia plate begins its descent into the mantle at the Sunda trench, which lies to the southwest of the earthquake's epicenter. At this latitude, the trench is the surface expression of the plate interface between the Australia plats and the Sunda plate.

In the region of the earthquake, the Australia plate moves toward the northeast at a rate of about 5 cm/year relative to the Sunda plate. This results in oblique convergence at the Sunda trench. The oblique motion is partitioned into thrust-faulting, which occurs on the plate-interface and which involves slip directed perpendicular to the trench, and strike-slip faulting, which occurs several hundred kilometers northeast of the trench and involves slip directed parallel to the trench. The March 28 earthquake occurred as the result of thrust faulting.

This earthquake was likely triggered by stress changes caused by the December 2004 (M9.0) earthquake. However, it occurred on a segment of the fault 100 miles (160 kilometers) to the southeast of the rupture zone of the M9.0 Sumatra earthquake.

The most recent magnitude 8+ earthquake in the immediate region of this earthquake occurred in 1861. The 1861 earthquake generated a regionally destructive tsunami. Another earthquake of similar magnitude occurred further south in 1833.

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Paris, 28 March 2005: 20:30 Paris time: The earthquake occurred around 23h15 local time between the Sumatran cities of Padang and Medan. The tremor continued for about 2 minutes. The epicentre was 2.3 NORTH 97.1 EAST, ie about 200 km off Sumatra mainland.

USA's NOAA has recommended that coastal populations within 1000 km from the epicentre be evacuated. Officials on Nias say that some people have been killed and dozens may be buried under rubble. Mass panic was caused by the eartyhquake with people running in the streets.

At this time (2300 Paris time) there is no evidence of a tsunami developing in the region. Thailand, Indonesia and Nicobar Island issued precautionary warnings. Thailand has now cancelled its alert.

The BMG (Geophysical Data and Information Center) in Indonesia has not reported a tsunami on Nias Island which is located very close (a few ten km) to the epicentre.

The information bulletins were broadcast to the subscribers of the tsunamiwarning-ioc mailing list.