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Dec. 29, 2004 � This is the preliminary timeline posted by NOAA four days after the tsunami event. It was based on initial phone conversations and reports from staff at the NOAA Pacific Tsunami Warning Center in Ewa Beach, Hawaii. Click here to find an updated timeline posted Jan. 28, 2005. The updated timeline contains more information on the sequence of events, as well as clarification and correction of items in this preliminary timeline, based on NOAA's continuing review of events immediately following the tsunami.

(All times listed below are Hawaii Standard Time or HST.) [Click here for view the updated timeline of Jan. 28, 2005.]

At 2:59 p.m. Hawaii Standard Time (HST) on Christmas Day a large earthquake occurred in the Indian Ocean near Sumatra, Indonesia.

At 3:07 p.m. the resulting seismic signals received at the NOAA Pacific Tsunami Warning Center (PTWC) from stations in Australia triggered an alarm that alerted watchstanders.

At 3:10 p.m. PTWC issued a message to other observatories in the Pacific with its preliminary earthquake parameters.

At 3:14 p.m. PTWC issued a bulletin providing information on the earthquake and stating there was no tsunami threat to the Pacific nations that participate in the Tsunami Warning System in the Pacific (ITSU). These member nations are part of the UNESCO Intergovernmental Oceanographic Commission (IOC) and the International Coordination Group for the Tsunami Warning System in the Pacific (ICG/ITSU). India, Sri Lanka, and the Maldives are not part of the Pacific system.

At 4:04 p.m. PTWC issued bulletin No. 2 revising the earthquake magnitude to 8.5. That bulletin stated no tsunami threat to the Pacific but identified the possibility of a tsunami near the epicenter. No additional information regarding the formation of a tsunami was available.

At approximately 4:30 p.m. HST PTWC attempted to contact the Australia Met Service with no luck but were successful in contacting Australia Emergency Management. They confirmed they were aware of the earthquake.

At approximately 5:30 p.m. Internet newswire reports of casualties in Sri Lanka provided PTWC with the first indications of the existence of a destructive tsunami. Indications are that the tsunami had already struck the entire area by this time, although we have not been able to obtain arrival times.

At approximately 5:45 p.m., armed with knowledge of a tsunami, PTWC contacted the U.S. Pacific Command (PACOM) in Hawaii.

At approximately 5:45 p.m., PTWC received a call from a Sri Lanka Navy Commander inquiring about the potential for further tsunami waves from aftershocks.

At approximately 6:00 p.m. the U.S. Ambassador in Sri Lanka called PTWC to set up a notification system in case of big aftershock. He said they would contact Sri Lanka Prime Minister's office for such notifications.

Continuing news reports gave increasing and more widespread casualties.

At approximately 7:25 p.m. the first reading from the Australian National Tidal Center gauge at Cocos Island west of Australia gave a reading of 0.5m crest-to-trough.

At 7:25 p.m. the Harvard University Seismology Department reported its preliminary Centroid Moment Tensor solution that indicated a magnitude of 8.9.

At approximately 7:45 p.m. PTWC contacted the Australia Bureau of Meteorology and advised them about the increased earthquake magnitude and the 0.5m reading at Cocos Island, as well as the possibility of a destructive tsunami impact on Australia's west coasts.

At approximately 8:00 p.m. PTWC re-contacted PACOM to advise of increased earthquake magnitude and potential for further tsunami impacts in the western Indian Ocean.

At approximately 8:15 p.m. Australia Bureau of Met called PTWC to advise they had issued an alert to their west coast.

At approximately 8:20 p.m. the NOAA National Weather Service Pacific Region director contacted PTWC to report PACOM said no tsunami was observed at Diego Garcia in the Indian Ocean.

At approximately 10:15 p.m. PTWC spoke with U.S. State Department Operations and advised them about the potential threat to Madagascar and Africa. They set up a conference call with the U.S. embassies at Madagascar and Mauritius, and PTWC advised them of the situation.

At 5:36 a.m. on December 27 PTWC issued a third Tsunami Information Bulletin for this event informing the Pacific that small sea level fluctuations from the Indian Ocean tsunami were being observed in the Pacific, probably from energy that wrapped around south of Australia.