Miscellaneous - http://maxpages.com/victoriaclub5/Quack

The earthquake was initially reported as 6.8 on the Richter scale. The Pacific Tsunami Warning Center (PTWC) also estimated it at 8.5 shortly after the earthquake. On the moment magnitude scale, which is more accurate for quakes of this size (http://earthquake.usgs.gov/faq/meas.html), the earthquake's magnitude was first reported as 8.1 by the US Geological Survey. After further analysis, this was increased to 8.5, 8.9, and finally to 9.0 (http://earthquake.usgs.gov/recenteqsww/Quakes/usslav.htm). Since 1900 the only earthquakes recorded with a greater magnitude were the 1960 Great Chilean Earthquake (magnitude 9.5), the 1964 Good Friday Earthquake in Prince William Sound (9.2), and the March 9, 1957 earthquake (http://neic.usgs.gov/neis/eq_depot/usa/1957_03_09.html) in the Andreanof Islands (9.1). The only other recorded earthquake of magnitude 9.0 was in 1952 off the southeast coast of Kamchatka (http://neic.usgs.gov/neis/eq_depot/world/1952_11_04.html) (see Top 10 earthquakes) (http://neic.usgs.gov/neis/eqlists/10maps_world.html)). Each of these megathrust earthquakes also spawned tsunamis (in the Pacific Ocean), but the death toll from these was significantly lower; a few thousand for the worst one, probably because of the lower population density along the coasts near affected areas and the much greater distances to more populated coasts. The hypocentre was at 3.316°N, 95.854°E, some 160 km (100 miles) west of Sumatra, at a depth of 30 km (18.6 miles) below mean sea level (initially reported as 10 km). This is at the extreme western end of the Ring of Fire, an earthquake belt that accounts for 81 percent of the world's largest earthquakes (http://earthquake.usgs.gov/faq/hist.html#1). The earthquake itself (apart from the tsunami) was felt as far away as Bangladesh, India, Malaysia, Myanmar, Thailand, Singapore and the Maldives. The earthquake was unusually large in geographical extent. An estimated 1200 km (750 miles) of faultline slipped about 15 m (45 ft) along the subduction zone where the India Plate dives under the Burma Plate. The slip did not happen instantaneously but took place in two phases over a period of several minutes. Seismographic data indicate that the first phase involved the formation of a rupture about 400 km long and 100 km wide, located 30km beneath the sea bed. The rupture proceeded at a speed of about 2 km/s, beginning off the coast of Aceh and proceeding north-westerly over about 100 seconds. A pause of about another 100 seconds took place before the rupture continued northwards towards the Andaman and Nicobar Islands (http://www.guardian.co.uk/life/feature/story) The India Plate is part of the great Indo-Australian Plate, which underlies the Indian Ocean and Bay of Bengal, and is drifting northeast at an average of 6 cm/year (2 inches/year). The India Plate meets the Burma Plate (which is considered a portion of the great Eurasian Plate) at the Sunda Trench. At this point the India Plate subducts the Burma Plate which includes the Nicobar Islands, the Andaman Islands and northern Sumatra. The India Plate slips deeper and deeper beneath the Burma Plate until the increasing temperature and pressure turns the subducting edge of the India Plate into magma which eventually pushes the magma above it out through the volcanoes (see Volcanic arc). This process is interrupted by the locking of the plates for several centuries until the build up of stress causes their release resulting in a massive earthquake and tsunami. The volcanic activity that results as the Indo-Australian plate subducts the Eurasian plate has created the Sunda Arc. As well as the sideways movement between the plates, the sea bed is estimated to have risen by several metres, triggering devastating tsunami waves. The tsunami did not originate from a point source, as mistakenly depicted in many illustrations of their spread, but radiated outwards along the entire 1200 km length of the rupture. This greatly increased the geographical area over which the waves were observed, reaching as far as Mexico and Chile. 1.1) Aftershocks and other earthquakes

Numerous aftershocks were reported off the Andaman Islands, the Nicobar Islands and the region of the original epicentre in the hours and days that followed. The largest aftershock was 7.1 off the Nicobar Islands (http://earthquake.usgs.gov/recenteqsww/Quakes/ussmax.htm). Other aftershocks of up to magnitude 6.6 continue to shake the region on a daily basis (http://wwwneic.cr.usgs.gov/neis/bulletin/). The earthquake came just three days after a magnitude 8.1 earthquake in an uninhabited region west of New Zealand's sub-Antarctic Auckland Islands, and north of Australia's Macquarie Island (http://earthquake.usgs.gov/recenteqsww/Quakes/ussjal.htm). This is unusual, since earthquakes of magnitude 8 or more occur only about once per year on average (http://earthquake.usgs.gov/faq/hist.html#8). Some seismologists have speculated about a connection between these two earthquakes, saying that the former one might have been a catalyst to the Indian Ocean earthquake, as the two quakes happened on opposite sides of the Indo-Australian tectonic plate (http://www.news.com.au/common/story_page). However the USGS sees no evidence of a causal relationship (http://earthquake.usgs.gov/eqinthenews/2004/usslav/neic_slav_faq.html). Coincidentally the earthquake struck almost exactly one year (to the hour) after a magnitude 6.6 earthquake killed an estimated 30,000 people in the city of Bam in Iran (http://earthquake.usgs.gov/recenteqsww/Quakes/uscvad.htm). As well as continuing aftershocks, the energy released by the original earthquake continued to make its presence felt well after the event. A week after the earthquake, its reverberations could still be measured, providing valuable scientific data about the Earth's interior (http://www.reuters.co.uk/newsArticle.jhtml?type=topNews). 1.2 ) Power of the earthquake

The total energy released by the earthquake in the Indian Ocean has been estimated as 2.0 exajoules (2.0×1018 joules) [16] (http://earthquake.usgs.gov/eqinthenews/2004/usslav/neic_slav_faq.html). This is enough to boil 150 litres (40 US gallons) of water for every person on Earth. It is estimated to have resulted in an oscillation of the Earth's surface of about 20 to 30 cm, equivalent to the effect of the tidal forces caused by the Sun and Moon (http://www.reuters.co.uk/newsArticle.jhtml?type=topNews). The shock waves of the earthquake were felt across the planet - as far away as Oklahoma, vertical movements of 0.12 in (3 mm) were recorded (http://www.muskogeephoenix.com/news/stories/20041228/localnews/1795857.html). The shift of mass and the massive release of energy very slightly altered the Earth's rotation. The exact amount is yet undetermined, but theoretical models suggest the earthquake shortened the length of a day by 2.68 microseconds (2.68 µs) (or about one billionth of the length of a day) [19] (http://www.nasa.gov/home/hqnews/2005/jan/HQ_05011_earthquake.html) due to a decrease in the oblateness of the Earth. It also caused the Earth to minutely "wobble" on its axis by up to 2.5 cm (1 inch) in the direction of 145° east longitude (http://slate.msn.com/id/2111443/), (http://www.cnn.com/2004/TECH/science/12/29/quake.wobble.reut/index.html) or perhaps by up to 5 or 6 cm (http://news.xinhuanet.com/english/2004-12/29/content_2389519.htm). However, due to tidal effects of the Moon, the length of a day increases at an average of 15 µs per year, so any rotational speedup due to the earthquake will be quickly lost. Similarly, the natural Chandler wobble of the Earth can be up to 15 m (50 ft). More spectacularly, some of the smaller islands southwest of Sumatra may have moved southwest by up to 20 m (66 ft). The northern tip of Sumatra, which is on the Burma Plate (the southern regions are on the Sunda Plate), may also have moved up to 36 m (118 ft) southwest. Movement was likely both vertical as well as lateral; some coastal areas may now be below sea level, making their reoccupation very unlikely. Measurements using GPS and satellite imagery are being used to determine the extent and nature of actual geophysical change.

Sign Guestbook

View Guestbook

VICTORIA CLUB 5
Rilbong Zig Zag Road
Shillong	Meghalaya	793004
India
0364-2502776 (Suubash Deb)/09863091423 (M.Barua)
victoriaclub5@victoriaclub5.cjb.net (Suubash Deb)

Visitors: 00151

Page Updated Mon Oct 16, 2006 8:14am EDT