The Elements Wrath: Earthquakes

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In recent years, every now and then, Alexandria would quiver a little, as we experience a mild Earth tremor; nothing to cause much alarm though, still people talk about it for a while since it is a rare occurrence. Others, however, are not as blessed as us; in some places, earthquakes are a habitual hazard, and drills are often carried out to make sure people are always prepared to flee to safety. One such place is the Indonesian Island of Sumatra, lying on an active fault line.

So, what exactly causes the ground to shake? Well, the theory is that the Earth's crust and upper mantle is composed of several large, thin plates that move in different directions, causing friction depending on the direction the plates are moving. Sometimes the plates crash together, pull apart or slide along each other; this movement is what usually causes earthquakes.

There are about 20 plates along the surface of the Earth that continuously, and slowly, move past each other. As one person puts it: “Imagine holding a pencil horizontally; if you were to apply a force to both ends of the pencil by pushing down on them, you would see the pencil bend. After enough force is applied, the pencil would break in the middle, releasing the stress you have put on it; the Earth's crust acts in the same way. As the plates move they put forces on themselves and each other; when the force is large enough, the crust is forced to break. When the break occurs, the stress is released as energy that moves through the Earth in the form of waves, which we feel and call an earthquake”.

One of the countries that experience many earthquakes is Japan; they can experience thousands of minor tremors each year. One of the worst earthquakes that Japan experienced in its history was the Kobe earthquake in 1995; nearly 27,000 people were injured, more than 45,000 homes were destroyed, and 6,433 people lost their lives. The destruction of the earthquake was devastating; Japanese scientists have since tried to improve prediction of earthquakes, but it is extremely difficult to predict when and where earthquakes will occur.

More recently, the 2011 Tohoku earthquake was of magnitude 9.0 on the Richter scale; a strength never recorded in modern times, making it one of the most powerful earthquakes. The epicenter was approximately 70 km east of the Oshika Peninsula of Tōhoku. As the Earth shifted during the earthquake, this movement triggered powerful tsunami waves that reached heights of up to 40.5 m in Miyako in Tōhoku's Iwate Prefecture; in the Sendai area, they travelled up to 10 km inland. Early estimates placed insured losses from the earthquake alone at USD 14.5 billion to USD 34.6 billion.

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SCIplanet is a bilingual edutainment science magazine published by the Bibliotheca Alexandrina Planetarium Science Center and developed by the Cultural Outreach Publications Unit ...
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