Earthquakes -the physical phenomena of ground shaking, surface fault rupture, and ground failure and, in some coastal areas, tsunamis. Smaller earthquakes, aftershocks, may follow the main shock, sometimes several hours, months, or even several years later.
Volcanoes-serious damage is restricted to small areas compared with the extent of damage from large floods or great earthquakes. Yet volcanic eruptions can take a high toll in human life and property.
Seismic stations consist of a seismometer for sensing ground motion, a clock for determining time, and a recorder for collecting data of earthquakes. They detect and measure Earth's ground motion.
