2 -- The Gujarat Quake

How Earthquakes Occur
The Gujarat Quake's Toll

 

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How Earthquakes Occur

The Earth is divided into different sections, called tectonic plates. Plate tectonics is the continual slow movement of these tectonic plates. This motion is what causes earthquakes and volcanoes and has created the most spectacular scenery around the world.

Earthquakes occur at plate boundaries. They occur in the crust or upper mantle, which ranges from the Earth's surface to about five hundred miles deep.

An earthquake is any sudden disturbance within the Earth occurring at the surface by a shaking of the ground. An earthquake is caused by a sudden slip on a fault. A fault is a fracture along which the blocks of the Earth's crust on either side have moved against each other. Stresses in the earth's outer layer push the sides of the fault tog ether. Stress builds up and the rocks slips suddenly, releasing energy that travels through the Earth's crust and cause the shaking that we feel during an earthquake. An earthquake occurs when plates grind and scrape against each other. To find out more about earthquakes click here.

Below is a picture of the plate boundaries. The Gujarat Earthquake occurred at the Indian and Eurasian plate. The trigger of the earthquake was said to be the Indian plate, moving Northeast at a rate of five centimeters per year, pushing against the Eurasian plate along the Himalayas. The pressure caused the Indian plate to develop cracks in several places. Scientists say the quake could have been a result of a slip in either the Allah Bund or the Narmadason fault region.

The destructiveness of an Earthquake is measured with a scale called the Richter scale. Below are the different ranges of the Richter scale.

The Richter Scale
Severity
Mild 0-4.3
Moderate 4.3-4.8
Intermediate 4.8-6.2
Severe 6.2-7.3
Catastrophic 7.3-8.9

To find out more about the Richter scale, click here.

 
The Gujarat earthquake occurred on January 26, 2001 at 8:49 in the morning. It lasted for only thirty seconds, but was nevertheless documented as the worst earthquake in independent India's history, measuring 7.9 on the Richter scale. Most, if not all, of the state's infrastructure, buildings and homes were destroyed. Below is a picture of the devastation. This is only one example of the suffering that occurred on that infamous day in January.

Anne L.

 

More on Earthquakes

Some issues that the recent tragedy in Gujarat brings to light involving earthquakes are how they happen, what their causes are and how we may be able to predict them so we can evacuate the people in danger. Sever earthquakes are extremely dangerous occurrences in which many people may be killed without warning. Plate tectonics is the most widely accepted scientific theory to explain earthquakes.

According to the theory of plate tectonics, the surface of the earth is broken up into many tectonic plates (see graphic A, below); all of which are moving over the mantel. Because these plates are moving--and not always in the same directions--they sometimes crash into each other, slide against each other, and pull away from each other. Plate boundaries where they are pulling away from each other are called a divergent boundaries. Earthquakes occur at all plate boundaries. One example of a divergent boundary is the Mid-Atlantic ridge in the middle of the Atlantic Ocean between Europe, Africa and the Americas. The bottom of the ocean is covered in volcanoes, creating new ocean floor as it spreads out. This type of boundary most often does not have earthquakes with a magnitude greater than 8 on the Richter scale. Another type of boundary is a transform boundary, where two plates are slipping across each other to as they move; this is the type of boundary that created the San Andreas fault. A third type of boundary is a convergent boundary. If this type of boundary is between two continents, it creates mountains when the land has no other place to go. This is how the Himalayas where created, and it was this type of boundary that caused the quake a Gujarat. If you are interested in a more detailed investigation of plate tectonics, look at these web sites:

http://www.pbs.org/wgbh/aso/tryit/tectonics/ (this is more elementary)
http://www.seismo.unr.edu/ftp/pub/louie/class/100/plate-tectonics.html (this is more advanced)



graphic A

 

Scientists believed that there would be too much friction with the ocean floor for it to be plausible, although they found fossils of the same type of animal on different contents that are now separated by the ocean. It would be nearly impossible for the animal to have gotten there if the continents were not together at some point in the past. Another piece of evidence for this is that there is coal in many cold places. Coal is an organic sedimentary rock that can only be formed in warm swampy places. Yet it is found in Antarctica, where it is neither warm nor swampy. The only possible explanation for the coal in Antarctica is that the climate there used to be very different; plate tectonics is the most likely explanation for this. Further support for the theory of plate tectonics is the spreading of the ocean floor. The ocean floor is being created at the Mid-Atlantic ridge and is being destroyed in trenches. We know that this is going on because the ocean floor closest to the coasts of North America and Europe are the oldest, and the rock forming the Mid-Atlantic ridge is the youngest. The rock on both sides of the Mid-Atlantic ridge preserved symmetrical patters (see graphic B, below), this would be extremely unlikely unless that the rock was flowing from the Mid-Atlantic ridge.


graphic B

 

One possible way to do this is with satellite GPS (Global Positing Systems), which could be used to detect tiny plate movements and stresses in the earth's crust. NASA is currently exploring this option. Another is using seismic waves to measure the amount of stress in the earth's crust near a certain city. Both of these methods are still experimental and require much more work before they will be ready for practical use. Although GPS is now used to detect larger plate movements (such as the spreading of the Atlantic Ocean) and has been a great help in outlining plates, it currently has little use in predicting earthquakes. It is at least true that it can not be done with enough accuracy to evacuate an area where an earthquake is predicated to occur; however, earthquake-prone areas should always be on alert, have and enforce earthquake resistance in building codes, and be prepared in case of an emergency. Gujarat had not effectively addressed many of these issues, which greatly added to the tragedy.

Jussie M.

 


 

The Gujarat Quake's Toll

On January 26, 2001, a natural disaster struck Gujurat, India. This earthquake measured 7.9 on the Richter scale and left a huge impact. The epicenter of the earthquake was Bhuj. Bhuj is the capital of Gujurat and is a major industrial city with advanced technologies. At the epicenter 90% of all the buildings were destroyed. In the surrounding cities like Ahmedabad and Surendrangar, 75% of all the buildings were either destroyed or damaged enough to be unfit for occupancy.

Since so many houses were destroyed or damaged, this quake left over 600,000 homeless. Furthermore, many of the people still are without adequate drinking water. On an average, the government testimates that it will take over two years just to repair the buildings and homes that were destroyed. It is also belived that the cost in damages is well over $5.5 million dollars.

Not only did the earthquake cause widespread damage and destruction to both rural constructions, but also urban buildings and industrial facilities.

 

Out of the last five earthquakes in India since 1988, only rural constructions were destroyed. These showed the vulnerability of the rural constructions of India. Yet this recent earthquake not only exposed how unstable rural constructions were, but it pointed out that even some of the engineering structures built with the traditional wisdom of design and construction in this country, are vulnerable.

Because so many buildings were destroyed, people started to blame the structure of the architecture. This event demonstrated numerous examples of geotechnical and structure failures. One example of this is the collapse of modern reinforced concrete (RC) frame buildings. The pictures shown here are all of RC frame building failures. Some other examples of geotechnical and structure failures are the collapse of earthen dams, bridges, and other industrial facilities. Knowing that these buildings (seismically deficient structures) will serve as a lesson for the rebuilding of the cities that were damaged.

Also, this earthquake alone affected over 15 million people in its 30-second duration. Tens of thousands died and 166,000 people were injured. Even livestock were reported affected by the quake; 12,250 heads of cattle perished.

Some Web sites that will help you get more of this kind of information are:

http://www.gisdevelopment.net/magazine/gisdev/2001/mar/sdsel.shtml
http://www.intrepidtravel.com/IndiaDetail.html
http://www.caa.org.au/world/sthasia/india/earthquake

Rebecca G.