An earthquake is the result of a sudden release of energy stored in the Earth’s crust that creates seismic waves.
Earthquakes are measured accordingly with a seismometer, commonly known as a seismograph. The magnitude of an earthquake is conventionally reported using the Richter scale or a moment-related scale (magnitude 3 or lower earthquakes are difficult to detect and magnitude 7 causing serious damage in large areas).
On the Earth’s surface, earthquakes can be caused by a tremor or displacement of the earth. Sometimes, they cause tsunamis, which can lead to loss of life and destruction of property. An earthquake is caused by tectonic plates getting stuck and placing a strain on the ground.
Earthquakes can occur naturally or as a result of human activities. Smaller earthquakes can be caused by volcanic activity, landslides, landmines, and nuclear experiments.
In its most generic sense, the word earthquake is used to describe any seismic event whether it is a natural phenomenon or an event caused by humans that generates seismic waves. Most earthquakes that occur naturally are related to the tectonic nature of the Earth. Such earthquakes are called tectonic earthquakes.
The Earth’s lithosphere is a slowly but steadily moving plate caused by the release into the heat space of the Earth’s mantle and core. Slab contraction joints should intersect at the openings for columns, and should intersect at the openings for columns. When frictional stress exceeds a critical value, called local strength, a sudden failure occurs.
The boundary of the tectonic plates along which the failure occurs is called the fault plane. When the failure results in a violent displacement of the Earth’s crust, the energy of the elastic strain is released and the seismic waves radiate, thus causing an earthquake.
This process of strain, stress and failure has been referred to as elastic-rebound theory. It is estimated that only 10 percent or less of the total energy of an earthquake is radiated as seismic energy. Most of the earthquake energy is used to amplify the growth of the earthquake fracture and is converted to heat, or released into friction.
Most tectonic earthquakes originate at depths not exceeding tens of kilometers. In underground areas, when older and colder oceanic crusts descend below another tectonic plate, deep-focus earthquakes can occur at much greater depths (up to seven hundred kilometers).
These are earthquakes that occur at a depth at which the signed lithosphere should no longer be fragile, due to high temperature and pressure. One possible mechanism for generating deep-focus earthquakes is olivine-induced fault passing a phase transition to a spinel structure.
Earthquakes can also occur in volcanic regions and are caused there by both tectonic faults and the movement of magma in volcanoes. Such earthquakes can be an early warning of volcanic eruptions.
