MALDIVES ONLiNE

The earthquake was initially reported as moment magnitude, Mw 9.0 (note that this is not the so-called Richter scale or local magnitude scale, Ml, which is known to saturate at higher magnitudes.) In February 2005 scientists revised the estimate of the magnitude to Mw9.3.[6] Although the Pacific Tsunami Warning Center has accepted these new numbers, the United States Geological Survey has so far not changed its estimate of 9.1. The most recent studies in 2006 have obtained a magnitude of Mw 9.1 to 9.3. Dr. Hiroo Kanamori of the California Institute of Technology believes that Mw = 9.2 is a good representative value for the size of this great earthquake. Reference: EERI Publication 2006-06, page 14 [www.eeri.org]

The hypocentre of the main earthquake was at 3.316°N, 95.854°E (3°19′N 95°51.24′E), approximately 160 km (100 mi) west of Sumatra, at a depth of 30 km (19 mi) below mean sea level (initially reported as 10 km). The earthquake itself (apart from the tsunami) was felt as far away as Bangladesh, India, Malaysia, Myanmar, Thailand, Singapore and the Maldives.

Indonesia lies between the Pacific Ring of Fire along the north-eastern islands adjacent to and including New Guinea and the Alpide belt along the south and west from Sumatra, Java, Bali, Flores, and Timor. The December 2004 earthquake actually occurred within the Alpide belt.[citation needed]

Great earthquakes such as the Sumatra-Andaman event, which are invariably associated with megathrust events in subduction zones, have seismic moments that can account for a significant fraction of the global earthquake moment across century-scale time periods. The Sumatra-Andaman earthquake was the largest earthquake since 1964, and the second largest since the Kamchatka earthquake of October 16, 1737.


Of all the seismic moment released by earthquakes in the 100 years from 1906 through 2005, roughly one-eighth was due to the Sumatra-Andaman event. This quake, together with the Good Friday Earthquake (Alaska, 1964) and the Great Chilean Earthquake (1960), account for almost half of the total moment. The much smaller but still catastrophic 1906 San Francisco earthquake is included in the diagram at right for perspective. Mw denotes the magnitude of an earthquake on the moment magnitude scale.

Since 1900 the only earthquakes recorded with a greater magnitude were the 1960 Great Chilean Earthquake (magnitude 9.5) and the 1964 Good Friday Earthquake in Prince William Sound (9.2). The only other recorded earthquake of magnitude 9.0 or greater was off Kamchatka, Russia, on November 4, 1952 (magnitude 9.0).[7] Each of these megathrust earthquakes also spawned tsunamis in the Pacific Ocean, but the death toll from these was significantly lower. The worst of these caused only a few thousand deaths, primarily because of the lower population density along the coasts near affected areas and the much greater distances to more populated coasts.

Other very large megathrust earthquakes occurred in 1868 (Peru, Nazca Plate and South American Plate); 1827 (Colombia, Nazca Plate and South American Plate); 1812 (Venezuela, Caribbean Plate and South American Plate) and 1700 (Cascadia Earthquake, western U.S. and Canada, Juan de Fuca Plate and North American Plate). These are all believed to have been of greater than magnitude 9, but no accurate measurements were available at the time.