Intensity is rated by how much damage was caused by an earthquake and how it affected people. Go to the University of Nevada-Reno Richter scale page for an excellent explanation of the Richter Scale and other earthquake quantifying tools. The UNR Seismological Laboratory Page is full of interesting information for earthquake enthusiasists. Look up Recent Earthquakes on the internet. Click the picture for more images of earthquake damage.
Primary effects are permanent features produced by the earthquake.
Examples include fault scarps, surface ruptures , and offsets of natural or human-constructed objects . An example you have already seen is the creek offset produced by movement along the San Andreas Fault. Secondary effects result when ground movement causes other types of damage. Examples include landslides, tsunami, liquefaction and fire. The amount of damage caused by an earthquake varies with magnitude.