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Thursday, September 1, 2011







Core facts





  • An earthquake is any motion of the ground, no matter 

what the cause. They range from being imperceptible to 


being so violent that they can raze cities. No part of the 


world is exempt from earth quakes. 

  • Earthquakes happen as a result of the release of energy            

when rocks come under pressure, mainly from plate  


movements, shift or fracture.



  • A few earthquakes are triggered by meteorite impacts,  

man-made explosions, or the weight of water, for instance 


behind a dam.

  • Earthquakes produce three main types of seismic

waves: primary (P),secondary(S) and surface(L).

  • Earthquakes  prediction the best defense against their

effects, is still an inexact science 












Where earthquakes happen











Most earthquakes occur at plate boundaries; 70 per cent

occur around the pacific, including the San Andreas fault 

region. Earthquakes also occur within continents, such as 

Tangshan in 1976. This map shows the regions with the 

greatest concentration of earthquakes activity.




How earthquakes happens?



An earthquake, the result of a sudden release of energy in 
the Earth’s crust, is measured with a seismometer. An 
earthquake with magnitude 3 or lower is mostly 
imperceptible while magnitude 7 can cause serious damage 
over large areas. The shaking in earthquakes can also 
trigger landslides and sometimes volcanic activity. In 
contrast, earthquakes are caused by volcanic activity,
landslides, and nuclear tests.


Seismic waves which carry with them an enormous amount 
of energy travel through the Earth’s crust. The earthquake 
which seismic waves cause will vary in strength and 
duration. This depends on the strength of the seismic 
waves. Let’s discover how earthquakes happen.

            Rock layers are forced upwards creating mountains at the place of plates’ collision.
                       Rock layers are forced upwards creating mountains at the place of plates’ collision.










                   Where plates diverge, lava emerges from the mantle and cools to from new sections of crust.
          Where plates diverge, lava emerges from the mantle and cools to form new sections of crust.






              
               Two plates move into each other or sliding past each other.
                                   Two plates move into each other or slide past each other.








                          Point of friction


                                                               Point of friction




                              
                             Primary waves (longitudinal or compressional waves) and S-waves (transverse or shear waves)
 Primary waves (longitudinal or compressional waves) and S-waves (transverse or shear waves)









                                    Surface waves radiable outwards from the epicenter which is the point directly above it at the surface of the Earth.
Surface waves radiable outwards from the epicenter which is the point directly above it on the surface of the Earth





Particle motion
Particle motion


Love waves, named after British mathematician A.E.H Love, is a surface wave having a horizontal motion that is transverse to the direction the wave is traveling.
Love waves, named after British mathematician A.E.H Love, is a surface wave having a horizontal motion that is transverse to the direction the wave is traveling.


The largest earthquake with 9.5 magnitude occurred on 22   

Indian Ocean earthquake, one of the largest recorded May


1960. Its epicenter was near Canute, Chile. The 2004 


earthquakes which have all been mega thrust earthquakes, 


is one of the deadliest earthquakes in history. In January 


2010, the worst 7.0 magnitude earthquake in two centuries 


struck less than ten miles from the Caribbean city of Port-


Au-Prices, Haiti, causing damages to Haitian.








Earthquake record




Place             Date    Key fact
Shanshi                      1556           highest know death toll - 830000 people died. china has 
 China                                               the worst record for earthquakes deaths


Lisbon                         1755           Worst in Europe - 8.7 on Richter scale. 70000 people died                                                 
Portugal                                            and the entire city was destroyed. Tremors were felt in North                             
                                                          Africa, England and Luxembourg.


Yakatut bay                1899           Greatest recorded vertical movement - the coast rose in                                      
 Alaska                                              places by 14.5m (47 ft).


San Franciso             1906            Destroyed most of the city, and a huge fire burned for 3
 USA                                                  days. Survivors included the celebrities Enrico Caruso and
                                                           John Barrymore. 


Off Chile                      1960            Largest earthquakes ever recorded - registered 9.9 on the   
                                                           Richter scale.         


Alaska                          1964          Longest recorded - 4minutes (Lisbon in 1755 was a 10-           
                                                          minute series of shocks).


Tangshan                    1976          Deadliest in the 20th century - 8.0 on the Richter scale.
China                                                655000 people died.


Kobe                             1995           Worst damage financially - over US$ 147 billion of damage.
Japan                                                 5500 people died.














                 Earthquakes gods






In the Bible, Yahweh speaks to the prophet Elijah as an 


earthquakes. In African myth earthquakes are caused by the  


dead of the underworld. The Greek god of earthquakes  was   


Poseidon , also god of sea. His roman counterpart was 


Neptune. In Siberia the earthquakes god is Tuil, who rides 


a sleigh beneath the earth.