Two hours after the quakes – one with a magnitude of 8.6, the other measuring 8.3 – the centre says “the threat has diminished or is over for most areas”.
The alerts caused panic as people fled buildings and made for high ground.
There have been no immediate reports of damage or casualties.
India, Thailand and Sri Lanka have also lifted their own tsunami warnings.
The US Geological Survey (USGS), which documents quakes worldwide, said the first Aceh quake was centred at a depth of 33km (20 miles), about 495km from Banda Aceh, the provincial capital.
It was initially reported as 8.9 magnitude but was later revised down to 8.6 by the USGS. Quake officials said a tsunami had been generated and was heading for the coast of Aceh.
What is a Tsunami? A tsunami is a sea wave, (more precisely, a series of waves), of local or distant origin that results from large-scale seafloor displacements associated with large earthquakes, major submarine slides, or exploding volcanic islands. A tsunami can be caused by a sudden vertical movement of a large area of the sea floor during an undersea earthquake and travels at speeds in excess of 450 mph.. The first wave is almost never the largest and damaging waves may potentially arrive for hours. A tsunami is sometimes called a tidal wave, but this term is a misnomer. Unlike regular ocean tides, tsunamis are not caused by the tidal action of the moon and sun.
What To Do: When you are at the beach and feel an Earthquake: A strong off-shore earthquake may generate a tsunami. Therefore, if you feel the ground shake, evacuate to high ground immediately and return only after officials say it is safe to do so.
Tsunamis along the Pacific Coast. From southern British Columbia to northern California, people and property are at risk both from distantly and locally generated tsunamis. Recent studies indicate that about a dozen earthquakes (with magnitudes of 8 or more) have occurred in the Cascadia subduction zone west of Washington. (Map) In 1946, a tsunami was initiated by an earthquake in the Aleutian Islands of Alaska; in less than 5 hours, it reached Hawaii with waves as high as 55 feet.(NOAA)
More recently, in 1964, a magnitude 9.2 earthquake occurred in Prince William Sound, Alaska. The shock generated a tsunami that deviated many towns along the Gulf of Alaska, and left serious damage at Alberni and Port Alberni, Canada, along the West Coast of the United States (15 killed), and in Hawaii. The maximum wave height recorded was 67 meters at Valdez Inlet. Seiche action in rivers, lakes, bayous, and protected harbors and waterways along the Gulf Coast of Louisiana and Texas caused minor damage. It was also recorded on tide gages in Cuba and Puerto Rico.(USGS)
To be recognized as TsunamiReady and StormReady, a community must:
Establish a 24-hour warning point and emergency operations center;
Have more than one way to receive tsunami and severe weather warnings and forecasts to alert the public;
Create a system that monitors local weather conditions;
Promote the importance of public readiness through community seminars;
Develop a formal hazardous weather plan, which includes training severe weather spotters and holding emergency exercises.
Both community preparedness programs use a grassroots approach to help communities develop plans to handle local severe weather, wave impacts, flooding threats and help communities inform citizens of threats associated with each. The program is voluntary and provides communities with clear-cut advice from a partnership between the local NOAA Weather Service forecast office and state and local emergency managers.
StormReady started in 1999 with seven communities in the Tulsa, Okla., area. Ocean Shore, Wash., became the first TsunamiReady community in 2001. There are now more than 860 StormReady communities in 47 states and 16 TsunamiReady communities along the West Coast of the U.S., Hawaii, and Alaska.
The NOAA National Weather Service is the primary source of weather data, forecasts and warnings for the United States and its territories. The NOAA National Weather Service operates the most advanced weather and flood warning and forecast system in the world, helping to protect lives and property and enhance the national economy.
NOAA is dedicated to enhancing economic security and national safety through the prediction and research of weather and climate-related events and providing environmental stewardship of the nation�s coastal and marine resources. NOAA is part of the U.S. Department of Commerce.
Relevant Web Sites
NOAA TsunamiReady Program
NOAA StormReady Program
NOAA Tsunami Warning System Receives High Marks
NOAA Tsunami Hazard Awareness
NOAA Tsunamis Page