Earthquakes are vibrations caused by the Earth's movements at plate boundaries and along fault lines. The most severe earthquakes are usually found at destructive and conservative plate boundaries.
The HYPOCENTRE (or focus) is the point at which the rock moves. The EPICENTRE is on the surface directly above the hypocentre.
The San Francisco earthquake of 1989 killed 67 people, left 2000 homeless and caused $4.5billion of damage. Sections of the Bay Bridge collapsed, the Nimitz highway (double-deck motorway) pancaked together and the Marina district, full of older houses, collapsed and fires erupted. It was only a moderate earthquake but the unstable ground resulted in LIQUEFACTION (where the ground moves like a liquid) which exacerbated the problems (made them worse).
Rescue teams searched for survivors, fires crews pumped water from the Bay to help put out the fires, electricity was restored within 2 days, the Bay Bridge was opened a month later but the Nimitz highway and Cypress Structure (plus many buildings) had to be redesigned to be earthquake proof. The government sent $3billion in aid to help.
A video on the effects of the Haiti earthquake and how the area is coping.
Buildings can be made 'earthquake proof' to try and reduce the impacts caused. Some examples are shown on the diagram.
A video on the Asian tsunami 2004