EARTHQUAKES, TSUNAMIS AND VOLCANOES
Earthquake: An earthquake is the shaking of the Earth's surface caused by the sudden release of energy in the Earth's crust. This release of energy results from the movement of tectonic plates along fault lines or from volcanic activity. The point on the Earth's surface directly above the origin of the earthquake is known as the epicentre.
Focus (Hypocentre): The point within the Earth where the earthquake begins is called the focus or hypocentreThe depth of the focus can influence the severity of shaking felt on the surface. Shallow earthquakes (within 70 km of the surface) tend to cause more damage compared to deeper earthquakes.
Magnitude: The magnitude of an earthquake refers to the amount of energy released during the event. It is measured using the Richter scale or the more modern Moment Magnitude Scale (Mw), which provides a more accurate estimate of large earthquakes. Each whole number increase on the magnitude scale represents a tenfold increase in amplitude and approximately 32 times more energy release.
Intensity: While magnitude measures energy, intensity refers to the effects of the earthquake at specific locations on the surface, measured using the Modified Mercalli Intensity (MMI) scaleIntensity is influenced by factors like distance from the epicentre, local geology, and building structures. For example, in the 1994 Northridge earthquake in California, even though it was a 6.7 magnitude earthquake, the intensity varied across the region, causing different levels of damage.
Earthquakes occur when there is a sudden release of energy due to stress that builds up along faults or tectonic plate boundaries. This stress is caused by the movement of tectonic plates, which can either collide, slide past one another, or move away from each other. When the stress exceeds the strength of the rocks, it leads to a rupture, and the stored energy is released as seismic waves.