The source of these vibrations is the center of an earthquake. These are caused by the shifting of rock, which rotates and creates friction. This friction releases energy in waves. The intensity of these waves varies due to different factors. The distance between the epicenter and the place where the earthquake has occurred is called the focal depth. An earthquake is divided into different types based on how far its focal depth is from the earth’s surface. The location below the earth’s surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the earth is called the epicenter.
A fault is a fracture in the earth's crust along which there has been movement. Most faults occur at plate boundaries, but they may also occur within the interior of plates and other fracture zones. There are three main types of faults, strike-slip, dip-slip, and oblique-slip. Many faults are a combination of two or more of these types.
The mantle and the core are so hot and dense that they can't move on their own. Instead, they move because of the movements of the crust. The Earth’s crust is not one solid piece but instead a bunch of plates that are moving in different directions. This is caused by convection within the mantle, the movement of massive pieces within the mantle, and other geological phenomena.
Earthquakes in volcanically active areas that are caused by movement of magma in volcanic conduits are often referred to as volcano earthquakes. However, that term is misleading; there is little to no seismic activity observed prior to eruptions. It is now more common for such earthquakes to be called non-volcanic seismicity or earthquake swarms, and may even be regarded as a symptom of volcanic unrest if it occurs on the flanks of an active volcano.
Earthquakes also occur as a result of mining or quarrying activities that cause activities at great depths. This is the type of earthquake that generally results in greater damage and death tolls than any other natural phenomenon. Most of the mining-induced earthquakes occur in places like Japan, China, Turkey, India, etc.
The focus of an earthquake is the point on the Earth's surface where forces within the Earth caused by the earthquake are exactly balanced by the gravity force. The focal depth is usually approximately equal to the distance between the focus and the center of the Earth. Most earthquakes originate at a point on a fault plane that lies above a deep focus. The earthquakes are divided into three zones: shallow, intermediate, and deep based on their depth which range between 0 – 700 km.
Every large earthquake generates seismic waves that travel outward from the fault on which it occurs. The energy from this vibration travels through Earth in waves called seismic waves. The magnitude, or size, of the earthquake, is most commonly reported in terms of the Richter magnitude scale, but may also be reported using the moment magnitude scale.
A seismometer detects seismic waves below the instrument and records them as a series of zig-zags, or alternatively, as a continuous tone. Scientists can determine the time, location and intensity of an earthquake from the information recorded by a seismometer. This record also provides information about the rocks the seismic waves traveled through.
Magnitude is the amount of energy released when an earthquake occurs. A magnitude is a number that represents the amount of energy released. The higher the number, the more energy was released during the earthquake. To calculate magnitude, look at the amplitude and squared amplitude (area under the curve). The amplitude is the height of the wave from the tremor and the squared amplitude is how much area was covered on paper.
The intensity scale is named after Mercalli, an Italian seismologist. The intensity scale takes into account the visible damage caused by the event. The range of intensity scale is from 1-12.
