Seismology is the study of earthquakes.
Earthquakes are classified by their
appearance on a seismograph.
| Earthquake Type | Comments |
| High-Frequency | Dominant frequencies from 5-15 Hz. Caused by shear failure or slip on faults. Volcanic earthquakes = Rock breaking or explosion events. |
| Low-Frequency | Dominant frequencies between 1-5
Hz. Caused by fluid pressurisation processes. Volcanic earthquakes = movements of fluids, steam or gas (rarely liquid magma) imparting a slower shaking or rocking to the ground). |
| Hybrid | Contain both high and low frequency signals. Represent a mixture of processes. |
| Explosion | Caused by explosive eruptions. Signal contains an air-shock phase as well as an ground wave. |
| Tremor | Tremor is a continuous signal with
a duration of minutes to days. Dominant frequencies are 1-5 Hz. a) Harmonic Tremor has a smooth amplitude. b) Spasmodic Tremor has irregular signals. |
| Very-Long Period | Periods of 3 to 20 seconds. Associated with eruptions or vigorous fumarolic activity. |
| Superficial | Non-volcanic processes can produce
seismic signals. Examples: glacial movement, shore ice, landslides, rockfalls, and floods. |