Earthquake - the result of a sudden release of energy in the earths crust that creates seismic waves, and causes the earth to shake.

What causes earthquakes?...

The energy and stress built up in the earths crust at the plate boundaries, and released where there are faults on the surface of the earth, which causes the earth to shake.  

How do we measure them???

We measure earthquakes with devices called seismometers, but in this picture is a tool we used in the earlier years and it is a seismogram.

Where do they occur???????
Earthquakes mostly occur where there is a strike slip plate boundary or where there is a fault in the earths crust. When they happen in the ocean if the earthquake is big enough usually cause tsunamis, which are huge water waves that come from the ocean and hit land.

What Damages earthquakes do to the earth.

Earthquakes cause quite a bit of damage to the earth depending on the size. They go from cracking sidewalks and walls in houses, to fully destroying cities and knocking down buildings. Sometimes they cause fires because of the gas lines breaking and not flexing while the earthquake is going on. Causing way more damages and death rates to go up.

Biggest quakes to occur....
-Chile 1960 9.5 magnitude
-Alaska 1964 9.4 magnitude
-Sumatra 2004 9.3 magnitude