Friday, April 16, 2010

What is an Earthquake?

An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. Earthquakes are recorded with a seismometer, also known as a seismograph. The moment magnitude (or the related and mostly obsolete Richter magnitude) of an earthquake is conventionally reported, with magnitude 3 or lower earthquakes being mostly imperceptible and magnitude 7 causing serious damage over large areas. Intensity of shaking is measured on the modified Mercalli scale.
At the Earth's surface, earthquakes manifest themselves by shaking and sometimes displacing the ground. When a large earthquake epicenter is located offshore, the seabed sometimes suffers sufficient displacement to cause a tsunami. The shaking in earthquakes can also trigger landslides and occasionally volcanic activity. The origin point of seismic waves is called epicenter of earthquake. If epicenter is located near the sea then it can cause the creation of Tsunami waves. Earthquakes lead to severe shaking of earth’s surface, landslides etc. Earthquakes are generally results of natural phenomena like geological stress, volcanic eruptions, landslides etc but earthquakes can also be induced by some human activities like mine blasts and nuclear experimentation etc. the first rupture point of earthquake is called focus hypocenter and epicenter is the point at ground level exactly above the hypocenter.


In its most generic sense, the word earthquake is used to describe any seismic event — whether a natural phenomenon or an event caused by humans — that generates seismic waves. Earthquakes are caused mostly by rupture of geological faults, but also by volcanic activity, landslides, mine blasts, and nuclear experiments. An earthquake's point of initial rupture is called its focus or hypocenter. The term epicenter refers to the point at ground level directly above the hypocenter.

Those earthquakes which occur due to some natural phenomena are generally more intensified and harmful. These Tectonic earthquakes can occur just anywhere in earth where enough elastic strain energy is stored to conduct fracture propagation at a fault plane. There are basically 3 types of faults, which cause creation of the earthquakes- reverse, strike-slip and normal. Reason of a certain displacement decides the intensity of the earthquakes. Earthquakes are classified as extreme destruction source of nature because an exact warning can’t be extracted about earthquakes. Even sometimes earthquakes can hit a region in a series. In this situation one new earthquake gets triggered due to displacement, shaking or stress induction by previous strike of earthquake. This situation is called earthquake storm. This is extremely detrimental for human life and property.

Shaking of ground causes severe damage to the buildings or other structures on the ground including houses etc. Shaking of ground at a particular place depends upon the distance of that place from the epicenter. Severe shaking of ground causes destruction of all the buildings of a city and many people die by burring into the building materials.