"Seismic activity" is defined as the vibration of the ground due to the release of elastic energy from the breakage of rock within the earth or an explosion. The phenomenon is commonly referred to as an earthquake, but while seismic waves can be either body waves or surface waves, an earthquake radiates seismic energy as both types of waves.
Most seismic activity is caused by the movement of tectonic plates. As these plates shift, rocks around the boundaries of the plates are deformed, which then causes elastic energy to be stored. When pressure leads to a fault segment slipping, the results can be extraordinary. Seismic activity has many other causes as well, including crustal loading, volcanic or hydrothermal activity, and the re-activation of very old faults.
Humans may also cause seismic activity through fluid injection, reservoir filling or demolitions. To record seismic wave motion, scientists measure seismic activity with a seismograph, which is a very sensitive instrument that very accurately reads the magnitude and location of the seismic activity being picked up.
While it may be very destructive, seismic activity is also responsible for many treasured landscapes and topographic locations that people enjoy for their beauty and unique features. Many national parks, for example, are in areas where large earthquakes or other plate tectonic activity occurred in the past.