US Geological Survey Earthquake Hazard Program (http://earthquake.usgs.gov/)

National Geophysical Data Center (Earthquake Data) (http://www.ngdc.noaa.gov/seg/hazard/earthqk.shtml)

CEOSR Earthquake Monitoring Station (http://cervone.gmu.edu/cquake/)

"How Earthquake work" (http://howstuffworks.lycos.com/earthquake.htm/printable) by Tom Harris is a well written article for beginners.

The Nature of Earthquake Hazard

A sudden, violent shaking or movement of part of the earth's surface caused by the abrupt displacement of rock masses, usually within the upper 10 to 20 miles of the earth's surface. The earthquake hazard may consist of:

Ground Motion
Vibration and shaking of the ground during an earthquake is the most far-reaching effect and causes the most damage to buildings, structures, lifelines, etc.

Ground Surface Fault Rupture
The ground shaking is the result of a rupture of a fault beneath the surface. When the ground shaking results in a rupture of the surface of ground, an opening of up to 20 feet may occur.

Liquefaction
The ground temporarily loses its strength and behaves as a viscous fluid (similar to quicksand) rather than a solid.

Landslides
Sometimes an earthquake causes a landslide to occur. This involves a rock fall and slides of rock fragments on steep slopes.

Tsunamis
Tsunamis are sea waves produced by an undersea earthquake. These sea waves caused by the earthquake can reach 80 feet and can devastate coastal cities and low-lying coastal areas.

Secondary Hazards
Consequences of earthquakes may include fire, or dam failure, among others.

Risk Area

Earthquakes occur on all types of lithospheric plate boundaries. However, subduction zones and areas of continental collision are noted for their very large earthquakes. Large earthquakes also occur in plate interiors but with a much lower frequency.

Seismic Hazard and Risk

Studies of seismic hazard and risk address the magnitude, estimate the amount of ground shaking that could occur, and delineate the associated geological hazards (landslide, liquefaction, etc.) that may occur as a result of a catastrophic earthquake. Further, a vulnerability assessment should have been prepared as part of the hazard analysis. The assessment provides the planning team information related to probable consequences and damages their jurisdiction may suffer if struck by an earthquake. It focuses on casualties and injuries; potential building losses and identifies the buildings most vulnerable to seismicity (including critical facilities such as hospitals, EOCs, mass care centers, emergency services organizations' work centers, water and waste management plants, power companies, etc.); medical needs versus available medical resources; loss of utilities and replacement/repair time; etc. caused by the earthquake and the collateral hazards it may trigger (e.g. fires, dam or levee failure, tsunamis, etc.)

Earthquake Prediction

Under Construction