Sudden release of energy in the Earth's crust that creates seismic waves
- Earthquakes are measured using observations from seismometers on a scale called Richter scale.
- Magnitude 3 or lower earthquakes are mostly almost imperceptible and magnitude 7 and over potentially cause serious damage over large areas.
- Intensity of shaking is measured on the modified Mercalli scale.
- When earthquakes strike a fault in clusters, they are called an earthquake storm. Each quake triggers its next with the shaking or stres redistribution.
- The largest earthquakes in historic times have been of magnitude slightly over 9, although there is no limit to the possible magnitude.
- An aftershock is an earthquake that occurs after a previous earthquake, the mainshock.
- Earthquake swarms are sequences of earthquakes striking in a specific area within a short period of time.
- Around 500,000 earthquakes occur each year, detectable with current instrumentation.
- The number of seismic stations has increased from about 350 in 1931 to many thousands today.
- The United States Geological Survey estimates that, since 1900, there have been an average of 18 major earthquakes (magnitude 7.0–7.9) and one great earthquake (magnitude 8.0 or greater) per year, and that this average has been relatively stable.
- The 23 January 1556 earthquake in the Shaanxi province, China, killing more than 830,000 people.
- 90% of earthquakes occur in a 40,000 km long region called the Pacific Ring of Fire which bounds most part of Pacific Plate.
- A Tsunami is a long-wavelength, long-period sea waves produced by the sudden or abrupt movement of large volumes of water, often because of a mid-sea or mid-ocean earthquake.