Here are a few pages on the basic concepts to explain seismology and earthquakes.
What is an Earthquake? – earthquake motion, stress
Earthquake Location – epicentre, hypocentre, centroid
Earthquake Size – Richter magnitude, fault dimensions
Earthquake Effects – Ground vibration, intensity
Earthquakes in Australia – Historical seismicity, characteristics
Why Monitor Earthquakes? – Hazard, vulnerability and risk
Dams and Earthquakes – Reservoir triggered earthquakes