Predicting Earthquakes

• 18 Jul 2020

Why in News

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