What is an Earthquake? Understanding the Science Behind Geological Disasters
What is an earthquake?
Earthquake is a type of geological disaster. Earthquake is a sudden slipping or movement of a portion of the earth crust mainly including subducted zone. It usually accompanied and followed by a series of vibrations. The earthquake of similar or lesser intensity that follows the main earthquake is called as after-shock and pre- shock.
The outermost part of the earth is called as crust. It is a solid one which has a thickness from 0-50km. Two types of crust can be observed as continental crust (less density) and oceanic crust (high density).
There are earthquake high zones in the crust. But countries in zones where it's less prone to earthquake, still have to consider as this is disaster where it can happen anywhere, any time because of some anthropogenic activities like construction of reservoirs, highways etc.
Where does an earthquake occur?
The earth crust is moving on mantle due to the convention currents that have been created due to mantle driven magma. Mantle consists convention cells due to magma composition and it's circular type movement. This movement creates a pressure in the continental and oceanic crust. Then the crust move towards different directions.
The earth crust is not continuous. It has 8-9 major tectonic plates and plate boundaries. There are two types of plate boundaries as convergent boundaries and divergent boundaries. The convergent boundaries form subduction zone where one tectonic plate moves down the other ( form volcanoes which is another type of natural disasters). Some places in the subduction zone have breakings of the crust which are called as faults.
The earthquake occurs along the faults, which are weak zones separating two tectonic plates. The forming of the faults and subsequently earthquake is due to tectonic forces (movement of crust). Since the earth crust slips along a fault, an earthquake is formed. The crust may only move a few inches to a few feet in a severe earthquake.
The pressure given by the tectonic plates is stored as energy inside the materials. But after certain time, the materials won't be able to bear that. Then the energy will be released by making fractures.
Several types of faults can be identified as normal fault, reverse fault and strike-slip fault.
Both reverse and normal faults can cause for tsunami since these have vertical displacement. These waves will radiate to a very long distance based on the energy released.
How an earthquake occur: Elastic Rebound Theory
The Elastic Rebound Theory explains about how an earthquake occurs. According to this theory, the blocks don't slide due to friction that is formed by tectonic forces. But the rocks are deformed. Then stress applies exceed friction in between materials. The rupture (breaking of materials) occurs when the stress within rocks exceed friction. The elastic energy stored in the system is released after the rupture. Then the energy waves radiate outward from the fault and an earthquake is formed. The earthquake waves will cause disasters within natural and man-made environment.
The focus and epicenter of the earthquake
The point within earth where faulting begins is the focus (hypocenter) of an earthquake. The X, Y coordinates and the depth is needed to demarcate this point. The epicenter of an earthquake is the point on the surface that is directly above the focus. Only X, Y coordinates are needed to demarcate this point. Knowing these two points is essential for the management of earthquake.
The basic types of earthquake waves
The radiation of the earthquake energy generates different waves. These different earthquake waves create different issues to the environment.
There are four basic types of earthquake waves.
1. Primary (P) waves
These are axial oscillations. Primary waves are body waves and the fastest waves. They travel through solids, liquids or gases. These are compression waves where material movement is in the same direction as wave movement.
2. Secondary (S) waves
These are shear oscillations and body waves which are slower than primary
