Introduction to Earthquake

WHAT IS EARTHQUAKE? (EQ)

An EQ is a sudden motion or trembling (shaking) of Earth caused by the abrupt release of energy that is stored in rocks (Thompson & Turk, 2007).

Source(s) of EQ:

• tectonic plate motion
• fault movement
• volcanic activity

1. Rock breaks and move along a fault to release strain that has gradually built up in the rock.
2. Volcanic activity

•      Tectonic forces acting deep in the earth may put a stress on the rock, which may bend or change in shape(strain).
•      If your bend a stick,your hands put a stress on the stick,its bending is the strain.

The focus of an earthquake is the point where rocks first break along a fault 

seismic waves radiate from the focus.The epicenter is the point on the Earth’

surface directly above the focus.

SEISMIC WAVES

1.        Body waves: seismic waves that travel through the Earth’s interior,spreading outward from the focus in all direction.
2.        Surface waves: seismic waves that travel on Earth’s surface away from the epicenter,like water waves spreading out from a pebble thrown into a pond.

BODY WAVES
P waves (compressional) 6–8 km/s.
Parallel to direction of movement (slinky),also called primary waves. Similar to sound
waves. 

S waves (shear) 4–5 km/s
Perpendicular to direction of movement (rope);Also called secondary waves. Result from
the shear strength of materials. Do not pass through liquid.

SURFACE WAVES

Love waves
Like S waves that have no vertical displacement.The ground move side to side in a
horizontal plane that is perpendicular to the direction the wave is propagating.

Rayleigh waves
Behave like rolling ocean waves.Unlike the ocean waves,Rayleigh waves cause the ground
to move in an elliptical path opposite to the direction the waves passes.

Destruction results form :

•       Ground shaking
•       Liquefaction of the ground
•       Flood 
•       Fire (damaging of electrical power and gas line)
•       Tsunami, or seismic sea waves
•       Landslide