The Quake-Catcher Network is designed to be an educational tool for describing earthquakes and earthquake science in the classroom. For this purpose, we include a demonstration program called QCNLive for learning using lesson plans. QCNLive is a free program and can be downloaded from this webpage.
Seismology is the scientific study of earthquakes and the propagation of vibrations through Earth. Earthquakes occur when a large amount of energy that is built up over time is suddenly released. This energy release usually takes the form of slip along faults, where rocks on different sides of the fault slide in opposite directions. The rupture (or slip) often causes sharp displacements at the fault and shaking in the ground near the fault. This shaking is measured by sensors called seismometers.
This process is similar to touching your fingers together so that the tips of the fingers are holding onto each other. If you pull your hands apart gently, but hold on tight with just your fingertips, then nothing happens. But if you pull harder, your fingertips let go, and your arms pull apart with a sudden snap. You and people near you can even hear the sound of the fingers quickly sliding by each other. The sound vibrations are very similar to seismic waves that travel through the Earth, and seismometers listen to seismic vibrations like your ears listen to sounds.
Three types of Faults
There are three types of faults, 1) Normal, 2) Reverse, and 3) Strike-Slip. The motion you made with your hands above is similar to a normal fault. If you clasp your fingers as you did before, but then pull sideways instead of apart, your fingers will slip by each other. This motion is like a strike-slip fault.
Earth’s crust and upper mantle are made up of many plates that are in slow, but constant motion. Most of the time there is little to no motion at plate boundaries, so forces build as plates try to slide by each other. Occasionally, the stress becomes too great, and large fault zones at the plate boundaries suddenly slip violently. Greater amounts of slip over larger areas cause more violent shaking. Most, but not all, earthquakes happen near plate boundaries.
In the figure above plate boundaries are shown in pink. Earthquakes are shown in red. Metropolitan areas are seen as lights at nighttime. Most, but not all, earthquake happen at plate boundaries, and many people live near plate boundaries.
IRISThe Incorporated Research Institutions for Seismology has a ton of great educational material related to earthquakes.
UPSeis – an educational site for budding seismologists.