Ionospheric Based Monitoring of Large Earthquakes

• 08 Apr 2020

Why in News

Recently, scientists of Indian Institute of Geomagnetism (IIG) have come up with a study of the signatures of recent large earthquakes into the ionosphere. The aim was to derive the seismic source characteristics from the ionosphere.

• The research is a part of the interdisciplinary program ‘Coupled Lithosphere-Atmosphere- Ionosphere-Magnetosphere System (CLAIMs)’ of IIG. CLAIMS focuses on energy transfer to the atmosphere during solid Earth processes such as earthquakes as well as tsunamis.
• IIG is an autonomous institution of the Department of Science and Technology.

Key Points

• Scientists noticed that the spatial distribution of near field co-seismic ionospheric perturbations (CIP) associated with the earthquake could reflect well the ground deformation pattern evolved around the epicentre.
  
  • These CIP were derived using the Global Positioning System (GPS) measured Total Electron Content (TEC).
    
    • The TEC is the total number of electrons present along a path between a radio transmitter and receiver.
  • The CIP distribution was estimated at ionospheric piercing point (IPP) altitude.
• Co-seismic Ionospheric Perturbations (CIP):
  
  • In general, the Earth crust uplift during any earthquake produces compressional (i.e. pressure) waves in the overlying atmosphere.
    
    • These waves propagate upward in the region of exponentially decreasing atmospheric neutral density, and thus, waves amplitudes increase with atmospheric heights.
    • On arrival at ionospheric heights, the waves redistribute ionospheric electron density and produce electron density perturbations (disruption) known as Co-seismic Ionospheric Perturbations (CIP).
• However, evolution of seismic/tectonically induced ionospheric perturbation is highly controlled by the non-tectonic forcing mechanisms.
• The major effective non-tectonic forcing mechanisms at ionospheric altitudes are the
  
  • orientation between the ambient geomagnetic field and seismic induced neutral wave perturbations.
  • orientation between the moving satellite line of sights and the wave perturbations.
  • ambient ionospheric electron density gradient.
• Challenge: The ionosphere is a highly dynamic region and the origin of any perturbations in ionospheric electron density can be traced to various origins either from above (e.g. solar, geomagnetic etc) or below (e.g. lower atmospheric, seismic etc) the ionosphere. This is a major challenge while identifying the CIP.
• Inference: The manifestation of CIP has to be seen in light of the prevailing non-tectonic forcing mechanisms.
  
  • In this line, it is believed that the present study may assist while designing a tool for the ionospheric based seismic source characterisation.

Ionosphere

• The ionosphere is defined as the layer of the Earth's atmosphere that is ionized by solar and cosmic radiation. It overlaps the mesosphere, thermosphere, and exosphere.
• It lies 75-1000 km above the Earth.

Source: PIB