Seismology is the study of seismic waves, energy waves caused by rock suddenly breaking apart within the earth or the slipping of tectonic plates. We know these as events as earthquakes. They can also be caused by explosions from volcanic eruptions and testing of nuclear bombs. Seismology also studies seismic waves deliberately induced by controlled explosions, large trucks, and construction equipment, usually to search for underground sources of petroleum and natural gas. Seismologists study earthquakes and their results, like tsunamis, and landslides. They may also monitor active volcanoes for tremors and signs of an impending eruption. They use seismographs and computer equipment to collect and analyze data on seismic events.