Explained: The science behind earthquakes
The scientific study of earthquakes is a comparatively new concept. Until the 18th century, not many descriptions of earthquakes were recorded and the cause for natural plate movements remained unknown. One popular theory suggested that earthquakes were caused by the air rushing out of the deep cavities in the earth's surface. Greek concepts proposing that wind movement caused earthquakes continued to exist till the latter part of the 19th century. After extensive research, it became possible to determine the various aspects of earthquake: Fault displacement, dimensions of displaced blocks, the velocity of rupture, and the location of its initiation. Earthquakes are ranked as the most terrifying natural phenomena to exist, far more destructive to human life and property than volcanic eruptions. Here’s all you need to know about it.
Why do earthquakes take place?
The earth’s crust consists of large tectonic plates and smaller plates within. These plates move towards each other to converge, move apart to diverge, and past each other to transform a boundary. Earthquakes happen due to a sudden release of stress along the fault lines in the earth’s crust. The continuous motion of the tectonic plates builds up a steady pressure in the rock strata on both sides of the fault lines until the stress is released in the form of a sudden jerk. The seismic wave energy grows through the ground and onto the surface producing a movement that we perceive as an earthquake.
The surface where the plates slip is called the fault plane. The location below the earth’s surface where the earthquake originates is called the hypocentre and the location above the surface of the earth for the origin is called the epicenter. Earthquakes also have foreshocks sometimes. These are movements that happen in the same place before the main earthquake that follows. Scientists can’t tell the difference between the two till the mainshock happens. Aftershocks also take place after the mainshock has passed, this is a smaller movement. The most commonly occurring earthquakes are the ones that happen at the boundaries of the tectonic plates.
Recording movements
The instruments for recording every kind of movement on the surface of the earth have led to making it possible to determine earth vibrations. The instrumental study of earthquakes is done through seismographs. These graphs produce recordings called seismograms. The instrument is set firmly on the surface of the earth with a heavyweight that hangs free. When the ground shakes due to an earthquake, the seismograph shakes too but the weight stays still. The spring through which the weight hangs absorbs all the movement. The difference between the moving part and the motionless part of the seismograph gets recorded.