There’ve been many earthquakes in the last couple of years. Be it the quake on Republic Day in Bhuj, Gujarat , in 2001, the Indian Ocean earthquake right after Christmas in 2004, the Haiti quake in 2010 which resulted in 3,16,000 deaths or the 9.03 magnitude upheaval that devastated Japan in 2011— survivors have stood mute witnesses to the destruction. Safety measures have increased over the years and more people are aware of what to do during an earthquake.
But how do earthquakes occur?
The earth’s surface is made up of tectonic plates. While moving, these plates bump into or slide under each other. Sometimes, they simply move away. This tears apart the surface of the planet. Every now and then, the pressure is so much that the plates move suddenly, in jerky movements. Most of the time, this sudden movement has no serious consequence, but there are times when it can wreak havoc on land. Out of the million earthquakes that occur annually, many are so light that they cannot even be detected.
Sizing up a quake
One way of measuring earthquakes is using the Richter scale. The Richter scale rates earthquakes on an exponential scale. In other words, a quake that measures one on the Richter scale can hardly be felt, but a quake that is rated two will be ten times stronger than the former, and so on. Any earthquake that measures five or more can be felt by almost everyone. The higher it measures on the scale, the greater the destruction.
While it is hard to predict when an earthquake will occur, it is possible to trace areas where they are mostly likely to happen.
The fiery ring
Take a world map and trace New Zealand, Japan, and go all the way down to South America. Now take a look at it. You will see that the line you’ve drawn is in the shape of a horseshoe. This band is the circum-Pacific seismic belt, more commonly known as the Ring of Fire , where most of the largest earthquakes occur. It is also home to over 75 per cent of the world’s active and dormant volcanoes.
As most of the earth’s surface is covered by water, a large number of earthquakes occur under water, and this, in turn, triggers seismic waves like the Boxing Day tsunami that caused widespread destruction on December 26, 2004.
Due to the extent of destruction that occurs, people feel that there has been a substantial rise in the incidence of quakes. However, experts in the field think otherwise. Dr. Arun Bapat, retired seismologist from the Central Power Research Institute (CPRI), Pune, explains that the apparent increase in earthquakes is an illusion. This has come about because of a rise in detection systems, through which even the smallest of quakes can be reported.
He says, “Until 1975-1979, our capacity for detection, though less, was spread over a large area. After 1984, we have started having more seismic networks operated by different states. As a result, detection potential increased considerably. Now, practically every state has detection systems. For instance, Karnataka has a large seismic network operated by the Bhabha Atomic Research Centre (BARC).” He further explains how more stations have now come up in the Andaman and Nicobar islands, as opposed to what was there before. “Armed with better potential to detect quakes, people are more aware as even the most minor quakes are now reported. This is probably why people feel that the number of quakes has increased over the years.”
Ten of the most devastating earthquakes since 1900 according to the United States Geological Survey (USGS)
1. Chile (1960) - 9.5
2. Great Alaska Earthquake (1964) - 9.2
3. Off the West Coast of Northern Sumatra (2004) - 9.1
4. Near the East Coast of Honshu, Japan (2011) - 9.0
5. Kamchatka (1952) - 9.0
6. Offshore Maule, Chile (2010) - 8.8
7. Off the Coast of Ecuador (1906) -8.8
8. Rat Islands, Alaska (1965) - 8.7
9. Northern Sumatra, Indonesia (2005) - 8.6
10. Assam – Tibet (1950) – 8.6
