A 6.8 Magnitude earthquake hit Japan on Monday, July 16, 2007. Considering the high magnitude, the loss of life was small – seven persons dead and hundreds injured. So what exactly is an earthquake?
(Image Courtesy: Environment News Service and Japan Meteorological Agency)
Wikipedia defines earthquakes as “the result from the sudden release of stored energy in the Earth’s crust that creates seismic waves”. I will try and explain that in simple words.
The earth is not a stationary, passive body. In fact, it is a very active and changes are continuously taking place inside it. The “solid” earth is actually made of four parts: the inner core which is solid, the outer core which is liquid, the mantle and the crust which are solid too.The crust is the thinnest layer and being relatively cold, it is brittle. The upper part of the mantle and the crust together make up the “lithosphere”.
(Image Courtesy: Nevada Seismological Laboratory)
The lithosphere is not contiguous, it is made up of several pieces like a jigsaw puzzle. However, these pieces – called tectonic plates – are continuously moving around, sliding past each other, colliding or moving away from one another. When these plates that are touching each other, get locked at the plate boundaries (while the rest of the plate is trying to move), it causes frictional stress. When this stress is exceeded beyond a certain value, these plates get unlocked and suddenly move relative to one another. This violent displacement is called an earthquake.
Here are some pictures that show devastation caused by earthquakes.
Collapse of the Hanshin Expressway Bridge in the Kobe, Japan earthquake of 1995.
(Image courtesy: University of Washington)
The 1906 earthquake damage in San Francisco, USA.
(Image courtesy: Science Photo Library)
The earthquake in Bhuj, India in 2001
(Image courtesy: International Federation of Red Cross and Red Crescent Societies)
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Copyright Kshitija Nadgouda.
