EARTHQUAKES AND FAULTS

Causes of Earthquakes
There are basically three types: 

1. VOLCANIC
2. TECTONIC
3. COLLAPSE
(Also man-made due to nuclear explosions) 

Tectonic Earthquakes 

Most earthquakes occur at plate margins due to tension, compression or shearing forces.
Rocks at plate margins are in constant motion and are being pushed, pulled, bent, twisted and folded.
Inevitably at some point they must break or crack to produce FAULTS!!
[Note – some rocks break much more easily than others]

What is a Fault?
A fault is a break or fracture between two blocks of rocks in response to stress.
Three types of stresses produce faults 1) Tension
2) Compression
3) Shear
One block has moved relative to the other block.
The surface along which the blocks move is called a fault plane.

 

There is a chicken and egg relationship between faults and earthquakes

1. 1)  It was initially thought that earthquakes caused faulting (but then what caused the earthquake?)
   
2. 2)  It was later realized that faulting produced the earthquakes.
   

          Thus earthquakes may occur because:-

1. a)  Rocks are initially broken to produce a fault.
   
2. b)  Movement or re-activation of an already existing fault.