Across the ages, humans have tried to explain natural phenomena, like earthquakes, through stories and myths. Indian mythology says that when the elephant that holds the world on his back gets tired, an earthquake occurs; Norse mythology describes an earthquake as Loki, the God of mischief and strife, struggling to escape his prison; and Japaneses mythology talks about the giant catfish Namazu thrashing about beneath the earth, causing earthquakes. So what does science have to say?
The Earth’s crust—the solid uppermost layer of the planet—is broken up into pieces called tectonic plates. Together they form the continents and the ocean-floors as we know them. But these pieces don’t quite fit together neatly like a jigsaw puzzle; the boundaries between the pieces are usually under stress. When this stress increases beyond the breaking point, the plates rearrange themselves in a snap, and the energy built up is released in what we call earthquakes.
Earthquakes are frequent, with several earthquakes occurring on the planet every day. Most quakes occur along the boundaries between tectonic plates, as two plates bump into each other. Just last month, four earthquakes hit north Indian. An earthquake's intensity is a measure of the energy that is released, and is given by a number on the Richter scale. India’s largest earthquake had a whopping 8.6 magnitude and the largest in the world was a 9.5 magnitude earthquake.
An earthquake can be devastating, of themselves and through after-effects like tsunamis. The damage an earthquake can cause to buildings and structures depends on the intensity of the earthquake and the distance to its epicentre. It also depends on the nature of the soil on which the building stands. After an earthquake, the bedrock is set into oscillations, and the energy of these oscillations propagate upwards through the different layers of the soil. There might even be an aftershock—an earthquake of a smaller magnitude that’s caused by the first large one—and it occurs as the crust around the displaced plate adjusts to the effects of the main shock.
What’s startling about an earthquake is that if it is powerful enough, it can even change a place’s geography. Evidence of unusual seismic activity in India, like the 2001 Bhuj earthquake that occurred inside the continental Indian plate, far from any lithospheric boundaries, and other recent earthquakes have led scientists to predict that in a few million years a large earthquake might give rise to a new mountain range that could separate North India from the southern part!