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Scientific Background on the Indian Ocean Earthquake and Tsunami


Compiled by Lareef Zubair,
Sri Lanka Meteorology, Oceanography and Hydrology Network and
The Earth Institute at Columbia University,
lareef@iri.columbia.edu
1-845-680-4424


Summary


Information relating to the submarine earthquake inbetween Aceh, Indonesia and Sri Lanka of the 26th of December, 2004 has been compiled here. This compilation archives much of the readily available scientific information. Aspects that were not immediately brought out by news reports were:

  • The 9.0 Earthquake at 6.58 hours at the epicenter (and in Sri Lanka) led to a sequence of 15 other quakes across the Andaman region.
  • While earthquakes could not be predicted in advance, once the earthquake was detected it would have been possible to give about 3 hours of notice of a potential Tsunami. Such a system of warnings is in place across the Pacific Ocean. However, there was no warning system in the Indian Ocean. In addition, coastal dwellers are educated in the Pacific littoral to get to high ground quickly following waves. However, those in the Indian Ocean were quite unaware.
  • Tsunamis are rarer in the Indian Ocean as the seismic activity is much less than in the Pacific. However, there have been 7 records of Tsunamis set off by Earthquakes near Indonesia, Pakistan and one at Bay of Bengal.
  • Earthquakes occur when any of the 12 or 13 plate collide at their boundaries. The present collision is due to compression between the Indian and Burmese plates. Scientists now believe that one plate that comprised the landmass from India to Australia has broken up into two. The initial 8.9 eruption happened near the location of the meeting point of the Australian, Indian and Burmese plates. Scientists have shown that this is a region of compression as the Australian plate is rotating counterclockwise into the Indian plate. This also means that a region of seismic activity has become active in the South Eastern Indian Ocean.
  • Tsunamis are not entirely unknown in Sri Lanka. For example, the Tsunami in 1883 generated by the Volcanoes at Krakatoa led to a surge of at least 1 m in Sri Lanka. The damage was much less then. However, one difference was that this particular episode happened in the month of August. In the month of December, under the North-East monsoon, the Equatorial Indian Ocean jet propagates along the equator from Sumatra (near the epicenter of the quake) slightly to the South of Sri Lanka and to Somalia. This may be why the impact of the quake led to severe impacts in Sri Lanka.
  • Once the large amount of pent-up energy in the compression zones of the plate boundaries have been released, it takes another buildup of energy for another event of similar magnitude. This is unlikely in the short-term. However, in the future, Indian Ocean littoral regions should generate and pay attention to earthquake and tsunami warnings and be aware of the interplay of the seasonal oceanographic currents.


Contents:

Lamont Doherty Seismographs for 25th and 26th December 2004
Records from the US Geological Survey
USGS: Warning System Could have Saved Thousands
USGS: Background on the Earthquake
World Seismic Activity from the Global Seismic Assessment Program
Compression near the Boundaries of the Indian, Burma and Australia Plates
Tsunamis affecting South Asia
Tsunamis affecting Indian Coastlines
1883 - Reports from Ceylon on the Tsunami
1941 Tsunami in the Bay of Bengal
Indian Ocean Equatorial Currents During December/January
Disaster Preparedness Forecasting and Warning for Tsunamis
Link to Disaster Links from Relief Web





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