What is an earthquake, and how is it measured?

An earthquake is the sudden shaking of the Earth’s surface caused by the release of energy from the Earth’s lithosphere. This energy release occurs due to the movement of tectonic plates, volcanic activity, or man-made activities like mining or reservoir-induced seismicity.

Causes of Earthquakes

1. Tectonic Plate Movement: Most earthquakes are caused by the movement of tectonic plates at fault lines. Plates may slide past each other, collide, or move apart, causing stress that eventually leads to an earthquake.
2. Volcanic Activity: Magma movement can also cause earthquakes, especially near active volcanoes.
3. Human Activities: Activities like mining, reservoir filling, or geothermal energy extraction can induce earthquakes.

Measurement of Earthquakes

Earthquakes are measured using two main scales: the Richter scale and the Moment Magnitude scale (Mw). The intensity and effects of earthquakes can also be described using the Modified Mercalli Intensity scale.

• Richter Scale:
  • Developed in 1935 by Charles F. Richter.
  • Measures the magnitude of the earthquake, which is the amount of energy released.
  • It is a logarithmic scale, meaning each whole number increase represents a tenfold increase in measured amplitude and approximately 31.6 times more energy release.
  • This scale is more effective for smaller, local earthquakes.
• Moment Magnitude Scale (Mw):
  • Currently the most widely used and accurate scale.
  • Measures the total energy released by an earthquake.
  • Unlike the Richter scale, it is more accurate for larger and distant earthquakes.
• Modified Mercalli Intensity (MMI) Scale:
  • Measures the intensity or effects of an earthquake on the Earth’s surface, buildings, and people.
  • It is a qualitative scale ranging from I (not felt) to XII (total destruction).
  • Based on observed effects rather than instrument readings.

Seismographs are the instruments used to detect and record earthquakes. They measure the seismic waves generated by the earthquake and help determine the epicenter, depth, and magnitude of the quake.