Earthquake- A Natural Disaster

An earthquake is an oscillatory violent movement of the earth’s surface that follows a release of energy in the earth’s crust.

Earth quake is one of the major natural disasters besides floods, hurricanes, tornadoes and windstorms. The history reveals that earth quake is responsible for the large scale deaths of human beings and animals together with the destruction of infrastructure like roads, buildings, schools and hospitals. The history of natural disasters shows that the earthquake, in Pakistan has been the single largest source of human killings and wide scale destruction of infrastructure including buildings, roads, water supply and sewerage lines and public as well private structures.

The 8th Oct, 2005 earthquake in Muzaffarabad and northern NWFP, has led to the death of approximately one lac people, two lac injured and more than five million made homeless.

Earthquake Terminology

Hypocenter The rupture point with in the earth’s crust represents the source of emission of energy. It is known as the hypocenter

Earthquake Terminology

Epicenter The epicenter is the point on the earth’s surface immediately above the hypocenter

Focal depth The focal depth is the depth of the hypocenter below the epicenter.

Epicentral distance Epicentral distance is the distance from the hypocenter to a given reference point

Seismic Waves

The energy released by earthquakes is propagated by different types of waves

Body waves

Surface waves include

Body waves originate at the rupture zone, include

P-waves (primary)

(particle movement parallel to the direction of propagation of the waves),

S-waves (secondary or shear waves),

(particle movement perpendicular to the direction of propagation).

Surface waves include

Raleigh waves

(Raleigh waves produces a circular motion analogous to the motion of ocean waves)

Love waves

(Love waves produce horizontal motion transverse to the direction of propagation

Types of Seismic Waves