What Causes an Earthquake

Natural calamities are predictable, but inevitable. One of them is earthquake! So what is an earthquake? In simple terms, one can call it as shaking and vibration of the earth. And what causes an earthquake to happen? Frequent volcanic activities and constant movement of tectonic plates underground are palpable causes of earthquakes.

Causes of Earthquakes

Basically, the earth crust is constituted of a solid core, molten magma mantle and the tectonic plates that constitute the crust. These plates are in constant motion due to the convection currents of the magma and hence are either sliding against each other or moving away from each other. Although there is constant motion under the grounds, none of these are felt by us.

Due to this constant motion over the years, mountains and valleys are formed, with the former being formed when plates converge, causing one plate to go below the other. However if the plates move in different direction, sliding against each other, due to the friction generated, some sections of these plates lock together, causing a lot of kinetic energy to build up. The line of intersection which contains the point of friction between these plates, is often known as the earthquake fault line. These earthquake fault lines are often called fractures in the earth's crust. So when the plates start moving, the stored energy is released from the point of intersection (also known as the hypocenter), in the form of an earthquake.

Types of Earthquakes

When an earthquake occurs, it always comes out in three waves, the primary (P-Waves: high frequency short-wavelength longitudinal waves), secondary waves (S-Waves: high frequency, short-wavelength, transverse waves) and surface waves (L-Waves: low frequency, long-wavelength, transverse waves).

Tectonic Earthquake
This earthquake is triggered when there is a lot of strain and stress exerted on the tectonic plates. For instance, if you take a twig and try to bend it, you can feel energy building up through the twig, until it snaps. Once snapped, the twig vibrates, releasing energy. The same is what happens in a tectonic earthquake. Here, let me explain with the example of San Andreas Fault in California, where two plates, the Pacific plate and the North American plate were involved. Both these plates were moving in northwesterly direction, with one moving faster, due to which the tension created due to the friction of the plates caused an earthquake. Tectonic earthquakes are most common and keep happening all the time under the earth's crust, in both land and the ocean.

Volcanic Earthquake
Volcanic eruptions can also cause earthquakes. Many a time, the acidic lava that is vented out cools down as soon as it comes in touch with the atmosphere outside. This cooling blocks the volcanic vent and the pressure built inside gets trapped. But the pressure needs to be released in some way or the other and so chooses the weakest of the volcanic plates to escape through. This eventually causes massive and powerful earthquakes that can also give rise to tsunamis, pertaining to the ripples it has created. A significant example of this type is the explosion of Krakatoa (of Indonesia), whose repercussion was a massive earthquake that rattled Java and Sumatra islands. However, volcanoes that vent out basic lava do not cause earthquakes.

Collapse Earthquake
Small ripples that occur in mines and underground caverns, are known as collapse earthquakes. These earthquakes are also factored by massive landslides, or a mine burst which could happen due to intense stress on the rocks constituting the mines, causing large masses of rocks to displace. This eventually leads to collapsing of a mine, and hence is known as a collapse earthquake.

Explosion Earthquake
Detonation of nuclear devices can also set of earthquakes, more commonly known as explosion earthquakes. This occurs, when enormous nuclear energy is released during underground nuclear explosions, which when bottled within, increases a thousand times more than the atmospheric pressure, in intensity. Surrounding rocks get vaporized, leaving behind a mammoth cavity which is many meters in diameter.

Some of the most earthquake prone regions are Japan, Indonesia, Java and Sumatra, New Zealand, Hawaiian islands and Andaman & Nicobar islands. One can observe, that islands and high mountain regions are most prone to earthquakes due to the active tectonic plate movement in such areas. Intensity of earthquakes is measured on Richter magnitude scale, which is calculated by comparing the maximum heights of seismic waves over a distance of 1000 kilometers, from the point of origin of the earthquake on the earth surface (which is also known as epicenter). And can you imagine how much energy is released during an earthquake? A magnitude of 2, releases 30 times more energy than what would have been released for a magnitudes of 1. So if the magnitude of earthquake, as on Richter scale is 8.6, then an enormous amount of energy as much as that of 10,000 atomic bombs is released from the earth! One of the interesting facts is that, these earthquakes keep happening all the time under the oceanic crust, which is not felt on land until the ripples created are of high intensity.

Effects of an earthquake can be very cataclysmic, depending on the magnitude. Hence, people in earthquake prone regions prefer to build wooden houses and do not use too many automobiles for commuting. This is one way to cut down on materialistic and life damage. Also the movements of birds and animals are watched closely, because any deviance observed in their behavior indicates coming of a natural calamity. One needs to be equipped with earthquake survival kit and follow earthquake safety procedure guidelines to handle the situation effectively, should any arise.