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). Now that the question, how earthquakes happen, is clear, let's study the four types of earthquakes:

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 ratted 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 energy 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. So how are earthquakes measured? 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! So now, one must have figured out, what causes an earthquake and how much energy is released during each occurrence. One of the interesting earthquake 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.