Written by Jaivir Dhingra, a grade 5 student.
An intense shaking of the earth’s surface is called an earthquake. It feels like a jolt followed by rolling and shaking of the ground for a few seconds. Earthquakes have rocked our planet for billions of years. Severe quakes generate violent vibrations that not only shake the ground but crack it open leading to devastation.
So, why do earthquakes occur?
Earth’s outer layer called the lithosphere has huge rocky plates that are placed together like a jigsaw puzzle. These plates, called the tectonic plates, constantly move, slowly and independently over the viscous mantle layer of the earth. When the plates scrape or collide against each other, it produces stress on the surface of the earth. When this stress increases beyond a certain level, the pent up energy ruptures the rocks and creates a fracture known as a fault. This sudden release of energy generates ground-shaking vibrations that constitute an earthquake.
There are three types of earthquakes based on how tectonic plates move – convergent boundary; divergent boundary; and transform fault. In convergent boundary earthquakes, the plates bang against each other leading to the formation of hills and mountains. In divergent boundary quakes, the plates move apart forming a rift zone giving rise to new ocean floors; while in transform fault quakes the plates slip against each other this earthquake is also called strike-slip.
Did you know that the effect of an earthquake can be felt over a thousand miles away? When an earthquake strikes, the shock is transmitted by vibrations called seismic waves. These travel in all directions from the quakes underground point of origin, the hypocenter. The place where it originates on the earth’s surface is called the epicenter. Some vibrations are very soft that we do not feel them, however, some are so strong that they can be felt over a thousand miles away.
Earthquakes are very deadly. They cause damage to life and property. Earthquakes under the oceans cause Tsunamis (huge waves) which are also extremely devastating, claiming many lives. National Earthquake Information Center (NEIC) locates an average of 50 earthquakes every day, or about 20,000 a year.
The study of earthquakes and their magnitude is known as seismography, and the instrument used to measure the magnitude of an earthquake is called Richter scale or seismograph. It records seismic activities in the form of zig-zag patterns. The Richter scale has ratings from 0 to 10. 0 indicates the lowest intensity of earthquake and 10 indicates the highest intensity. According to the US Geological Survey, the deadliest ever earthquake was recorded in Chile in 1960 with a magnitude of 9.4-9.6 on the Richter scale. In India, the worst earthquake was in 1934 in Bihar with a magnitude of 8.1 on the scale.
Did you know that seismic activity happens on other planets too? Yes, scientists have measured seismic activity on Earth’s moon and even on Mars, Venus,and the moons of Jupiter. From this information, scientists can learn more about these astronomical objects.