CHARACTERISTICS OF EARTHQUAKES
Earthquakes happen with no warning.there is not yet a way to predict magnitude or the intensity of an earthquake.According to Preserve Articles.com Earthquake prone areas are generally well identified and well known on the basis of geological features and past occurrences of earthquakes.Most damage are because of buildings.About 200 large magnitude earthquake occure in a decade. The exact spot underneath the surface of the earth at which an earthquake originates is known as focus while the point lying on the ground surface vertically above the focus is defined as epicenter of the earthquake. The seismic shocks originating at a depth of about. 50 km or less below the surface is termed as shallow focus earthquakes; otherwise, these are known as deep focus earthquakes. Earthquakes occur because stresses build up between the plates as one plate passes another. As the plates move past one another they don't do so smoothly, rather, they snag and grind, allowing energy to build up. When the plates eventually move again this energy is released as shock or seismic waves through the Earth's crust. The point at which this slippage occurs is called the FOCUS, whilst the point on the ground surface above the earthquake FOCUS is called the EPICENTRE. Seismic shock waves will emanate radially outwards from these points and their energy will reduce with distance. This is typical of destructive margins which account for 90% of the World's earthquakes where the Oceanic plate grinds under a Continental plate as on the East coast of Japan -see Kobe case study. They also occur at conservative margins, such as the San Andreas Fault line, where the North American plate and Pacific plate are grinding past one another.Earthquakes can also occur at constructive plate margins. Here, the earthquake is the result of magmas forcing its way between the plates, causing the earth to tremble. Collisional margins, where continental crust meets continental crust, can also have earthquakes as a result of the pressures generated by collision.You can measure earthquakes with two scales the Richter scale or the Mercalli scale according to cool geography .co.uk.There are many ways to survive an earthquake,we have another blog for that.