Tuesday, May 13, 2008

:: Earthquakes

Earthquakes: A quick guide

Relief efforts after the South Asian earthquake of 2005, which killed 75,000 people, was hampered by the region's terrain [File: ETA]

How earthquakes happen:

Earthquakes occur along the earth's tectonic plate boundaries, like volcanoes.

The plates move past each other on these 'fault lines'. Jagged parts of the plates get stuck as other parts keep moving. Once the plates have moved far enough the stuck area becomes released causing an earthquake.

Earthquake impacts:

Poor people and poorer nations are typically hit hardest by earthquakes. This is due to buildings in these countries being built to low safety regulations and quality.

Useful links
For resources, including photos and topographical maps, see the US Geological Survey's
learning links.The USGS has also produced high quality earthquake animations.For what to do in an earthquake, see the American Red Cross's home earthquake plan.For the latest alerts on global seismic activity, visit:• USGS Latest Earthquakes or• The Global Disaster Alert and Coordination SystemUPSeis also offers answers to frequently asked questions about seismology and earthquakes.The livelihoods of poor people are also more vulnerable than that of richer people.

For example, an earthquake in the southern Iranian city of Bam took just 12 seconds to destroy a city with a population of 120,000. In the December 2003 quake almost a quarter of the population was killed and virtually all of the survivors were left homeless.

A magnitude of 6.5 was recorded for the disaster, but the impact was greater for other reasons:

1. The quake occurred just 10km below the city.
2. Nearly the whole of the population was asleep at the time of the quake.
3. The vast majority of the city's buildings were old. Their roofs crumbled during the shock, leaving no air pockets for those suffocating underneath.

Time is crucial to saving lives during an earthquake. In Bam local rescue teams saved 157 lives after being deployed within minutes of the quake. However, the following major international effort by 27 countries rescued only 22 people.

Terrain is also important. The South Asian earthquake of 2005, which killed 75,000 people, was compounded by innumerable landslides caused by aftershocks. These blocked roads and stifled relief efforts.


Earthquakes are measured by magnitude, typically in line with Charles Richter's scale devised in 1935.

Magnitude is consistent no matter how strong shaking is on the earth's surface.

Shaking increases with the epicentre's – the location on the earth's surface directly above the centre of the quake – proximity to the earth's outer layer.

But a rough guide can be given as to the how different measurements are felt on the ground.

A measurement below 2.5 is usually not felt on the earth's surface.

Earthquakes between 7.0 and 7.9 are considered a major earthquake and would be expected to cause serious damage.

A quake above 8.0 can completely destroy communities near the epicentre.

Source: UPSeis

Source: Al Jazeera