3/28/2005 Sumatra Quake

Updated 4/2/2005

This 8.7M quake was centered off the West coast of Northern Sumatra. Earthquakes over Magnitude 8 are classified as "Great" Earthquakes. "Great" quakes are relatively rare and usually very destructive. By comparison, this earthquake was considerably larger than the 1906 San Francisco earthquake and indeed larger than any seen in the US outside of Alaska. Of course damage from any quake is due to a number of factors including density of population, building methods and materials, local geology and the duration of shaking. This quake struck at 4:09 PM (GMT) or 11:09 PM local time. Shaking lasted 3 minutes, which is a long time for an earthquake. There have been at least 518 people confirmed killed and thousands displaced. A few people were pulled alive from the rubble after 4 days. Worst hit was the island of Nias, where electricity and water supplies have been disrupted. Roads and runways across the island have large cracks across them and are in many cases unusable. Also hard hit was the nearby island of Simeulue. Fires have raged unchecked with fire fighting equipment buried in rubble.

Aid has been arriving from around the world. Some teams were already in place in nearby Aceh from the December quake and tsunami. Some of the areas devastaed then have seen more damage from this quake. Tsunami warnings went out around the Indian Ocean and people were evacuated from coastal areas in Sri Lanka, India, Thailand, Malaysia and Indonesia. However this time there was no tsunami.

This earthquake occured on a neighboring section of the same subduction zone that caused the December 26, 2004 tsunami. Scientists had been concerned that that quake would increase the pressure on parts of the zone that had not moved and this appears to be what happened here. This map shows the relationship between these two quakes and two other quakes that have occured in the same area in the past. You can see quite clearly how different sections of this zone will move at different times.

(See the Plate Tectonics page for more information on these processes.) The US Geological Survey (USGS) is an invaluable resource in understanding and tracking earthquakes. Here is the USGS report on this earthquake

See also the following news stories:

3/20/2005 Japan Quake

Updated 3/20/2005

This 6.4M quake hit 570 miles west of Tokyo, off the coast of the island of Kyushu, Japan at 01:53AM (GMT) or 10:53 AM local time. Some news reports rated the quake as a Magnitude 7, which would have been much more powerful than the 6.4 Magnitude reported by the USGS. Many buildings were damaged, utilities were cut off, 1 person was killed and another 250 were injured. Tall buildings swayed in Fukuoka. Numerous aftershocks have followed the main quake. Intial fears that the quake would generate a tsunami proved unfounded.

The damage from this quake was very much less than the Iranian quake of similar size just a month before. Hundreds of people died in that quake. Both areas are subject to frequent strong earthquakes, but Japan has done a much better job of preparing for the inevitable with strong earthquake resistant building codes. Even so, a large earthquake in an urban area can cause thousands of deaths and billions of dollars worth of damage, as demonstrated in Kobe.

Japan is subject to frequent earthquakes due to the interactions of the Pacific, Phillipines, North American and Eurasian Plates in this area of the world.

(See the Plate Tectonics page for more information on these processes.) The US Geological Survey (USGS) is an invaluable resource in understanding and tracking earthquakes.

See also the following news stories: