When an earthquake occurs the webicorder will show ground motions that vary in amplitude depending on the
size of the earthquake and the sensitivity of the seismograph. The height of the recorded waves on the webicorder
(wave amplitude) is a greatly magnified representation of the actual ground motion. The magnification is 50,000
times or more depending on the site. A recording of an earthquake has recognizable characteristics. Typically,
one can recognize the arrival of different wave types: P (the primary, fastest traveling waves) and S (shear waves).
Greater separation between P and S waves indicate increasing distance to the earthquake.
On these seismograms you may see a variety of signals. Examples of signals seen on the webcorders are local earthquakes,
volcanic tremor at Alaska's volcanoes, and earthquakes elsewhere in the world. Almost any earthquake in the world having
a magnitude greater than 5.5 will be seen on these webicorders.
Not all the wiggles seen on the seismograms are due to earthquakes. Anything that shakes the ground could be recorded.
For example rockfalls, icequakes in glaciers, and ground motion induced by high wind conditions and ocean waves are very
common at Alaska's volcanoes. Even a bear lumbering by will produce a signal. Electrical noise may also appear on the
seismogram. Such noise is usually easy to distinguish from earthquake generated signals because the noise is often "spikey"
in appearance. In addition, all stations have calibration pulses once every 12 hours. These will always be in red or clipped
(see annotated sample