Earthquakes are recorded with the help of an instrument known as a seismograph. This write-up tells you more.
A thin layer of broken and crushed rocks between two blocks of rock in the earth's crust is known as a fault. When there is a sudden slip on a fault, or when two faults collide, an earthquake occurs. The length of a fault can vary from few centimeters to thousands of kilometers.
When pressure builds up in the earth's outer layer it causes rocks to slip. When this happens, the energy in the form of waves travel through the entire length of the thin rock layers to cause an earthquake.
An instrument or a sensor that senses the motions of the outer crust of the earth is known as seismograph. A seismograph has sensors to record the ground motion of the Earth caused by seismic waves. The sensor is known as seismometer.
The recorded data is known as a seismogram. A seismogram is used to calculate the magnitude of an earthquake. The scientists use several seismograms that are placed both close to and far from the source of a quake in order to calculate and determine its magnitude.
For a given quake, the result of the calculations from various seismographs should give the same magnitude. The seismometers are capable of measuring the ground motion as small as 40 billionth of an inch or as big as 1 billionth of a meter.
An Italian seismologist, Giuseppe Mercalli, compiled a scale called Mercalli Scale in the year 1902. This scale relied on the intensity of the damage caused by an earthquake.
In 1934, Charles F. Richter, an American seismologist, invented a scale called Richter to calculate the magnitude of a quake. The Richter scale is used to calculate the amplitude of largest and strongest seismic waves, and is used even today.
The Richter calculation of magnitude is based on the logarithmic scale of base 10. The scale is measured in steps one upward. The measurement of each unit is ten times more than the previous unit.
For instance, if the magnitude of a quake is 7.0 on a Richter scale, it indicates the intensity of the disturbance of the ground motion is 10 times bigger than the quake that has the magnitude of 6.0 on the Richter scale.
Earthquakes cannot be prevented nor predicted, however, the areas that are prone can be identified. The materials that can withstand the shocks and the tremors of a quake should be used to construct buildings in quake prone areas.