Earthquake

EARTHQUAKE OR SEISMOLOGY

 

Earthquake: The ground vibrations, both feeble and strong, produced on the surface of earth due to any reason what so ever are described as earthquake.

 

or

 

It may also defined as "Violent shaking of earth's surface due to abrupt release of large amount of energy that has accumulate over a long time inside the earth".

 

It is important to mention that 90% of earthquake are naturals and about 10% are manmade  due to nuclear explosions, in volcano blast etc.

 

Earthquake Engineering or seismology :-

The branch of science that deals with the study of earthquake and the structure of the earth is termed as earthquake engineering or seismology.

 

Important term for earthquake engineering:-

 

(a) Focus or Seismic Center : The exact point or place inside the surface of the earth at which an earthquake originates is termed as focus or seismic center. It is also termed as Hypocenter. It is actually a point on the fault plane where slip or movements of tectonic plates occurs.

 

(b) Epicenter : The point or line on the surface of the earth lying vertically above the focus is termed as 'epicenter' or 'epicentral' line.

 

(c) Focal depth : The depth of focus from epicenter is termed as focal depth or simply the vertical distance between epicenter and hypocenter is called focal depth.

 

(d) Epicentral depth : The horizontal distance from the epicenter and any place of interest or discussion is termed as epicentral distance.

 

(e) Anticentre : The point on the surface of the earth diametrically opposite to the epicenter is called anticentre.

 

(f) Seismic waves : The wave transmitted in all the directions due to large  strain energy released from the focus during an earthquake are termed as seismic waves.

 

(g) Seismograph : An instrument which is used to record ground vibrations or surface displacements is termed as a 'Seismograph'.

These are used only record weak motion and unsuitable for record of high intensity vibrations. to record high intensity another instrument are employed name accelerographs.