Seismic events can result from natural causes such as fault movement and volcanic activity, or human activities such as mine blasts or injection of fluids into deep boreholes. The magnitude of and distance from a seismic event, along with other factors, determines the amount of shaking that may be felt at the surface. The most frequent seismic events have very low levels of shaking—most of which are undetectable without special instruments located very close to the epicenter of the event. Seismic events that are large enough to cause considerable ground shaking and result in damage to structures and loss of life occur infrequently. With few exceptions, these are naturally occurring earthquakes. Most seismic events triggered or induced by human activity produce only very low-level shaking; however, some instances of wastewater injection have reactivated faults and caused earthquakes of moderate magnitude (Ellsworth, 2013).
- Fact Sheet