Earthquakes are monitored using the seismic energy produced by a quake. The energy released during an earthquake is measured using a variety of instruments, including strainmeters, creepmeters and tiltmeters, and earthquakes are assigned a value on the Richter Scale reflecting their severity.
Creepmeters measure earthquakes using a wire run between piers on either side of a fault. By measuring the displacement between the two piers, seismologists can monitor whether a fault has slipped. Strainmeters are highly accurate devices that measure crust strain using cylinders buried 200 meters deep. Many of these devices are installed along known faults, such as the San Andreas Fault. Tiltmeters measure the rotation of the ground near a fault and use a variety of devices, including pendulums or liquid level devices, which are similar to the kind of level found in a toolbox.
The United States Geological Survey and other seismological associations around the world maintain data about earthquake activity at known faults and install new devices as faults are studied. Through programs such as NetQuakes, there are also opportunities to allow schools, homes or privately owned buildings to host a seismograph, allowing the USGS to maintain a large amount of information on earthquakes and other seismic shifts.