Predicting Earthquakes | 18 Jul 2020

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According to a recently published study, researchers have developed a new way to improve the prediction of earthquakes.

Key Points

  • Earthquakes:
    • Earthquakes usually occur along faults (fractures between rocks which can range from a few millimetres to thousands of kilometres).
    • When two blocks of earth slip past one another, seismic waves are generated in a short span of time and earthquakes occur.
      • The waves travel to the surface causing destruction and are difficult to predict, making it challenging to save lives.
  • Earlier Attempts:
    • Scientists have attempted to recreate the faults and their sliding in laboratories to try and understand the conditions in them during earthquakes.
    • However, the actual conditions are so complex that it is difficult to recreate them with full accuracy which makes the prediction of earthquakes difficult.
  • New Method:
    • Researchers have now used a different approach for earthquake prediction by trying to predict the frictional strength of phyllosilicates.
      • Frictional Strength: It is the force required to cause movement along a fault.
      • Phyllosilicates: Minerals in the form of thin plates found along the weakest part of the faults where earthquakes occur.
    • The researchers analysed artificial fault zones on a microscopic scale to identify processes that occurred during the experiment.
    • A set of equations were then formulated to predict how the frictional strength of phyllosilicate changes, along with a change in conditions such as humidity or the rate of fault movement.
    • This made it easier for modellers to simulate fault movement in natural conditions, including earthquakes.
    • The new model predicts that movement along phyllosilicate-rich fault zones becomes more difficult as it becomes faster and this has been consistent with experiments.
    • This behaviour of movement becoming more difficult prevents earthquakes and suggests minerals other than phyllosilicates play an important role in causing earthquakes.
    • However, more work and research is needed to clearly explain it and to understand the relation between the force that holds a fault together and the force needed to move the fault.

Seismic Waves

  • Vibrations from an earthquake are categorised as P (primary) and S (secondary) waves. They travel through the Earth in different ways and at different speeds. They can be detected and analysed.
    • P-waves:
      • These are the first waves detected by seismographs (instruments used to detect and record earthquakes).
      • These are longitudinal waves which means they vibrate along the same direction as they travel.
      • Other examples of longitudinal waves include sound waves and waves in a stretched spring.
    • S-waves:
      • These waves arrive at the detector after primary waves.
      • These are transverse waves which means they vibrate at a right angle to the direction in which they travel.
      • Other examples of transverse waves include light waves and water waves.
  • Both types of seismic waves can be detected near the earthquake centre but only P-waves can be detected on the other side of the Earth.
    • P-waves can travel through solids and liquids (since they are longitudinal waves) whereas S-waves can only travel through solids (as they are transverse waves). This means the liquid part of the core blocks the passage of S-waves.
  • The earthquake events are scaled either according to the magnitude or intensity of the shock.
    • The magnitude scale is known as the Richter scale. The magnitude relates to the energy released during the earthquake which is expressed in absolute numbers, 0-10.
    • The intensity scale or Mercalli scale takes into account the visible damage caused by the event. The range of intensity scale is from 1-12.

Source: DTE