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Japanese scientists detect rare deep-Earth tremor S wave microseism

Scientists in Japan studying earthquakes for the first time have detected a rare deep-Earth tremor, known as an S (secondary) wave microseism. Microseisms are very faint tremors.

The detection was made by scientists from the National Research Institute for Earth Science and Disaster Prevention in Japan.

Key Facts

  • The rare deep-Earth tremor S wave microseism was detected for the first time and traced its location to a distant and powerful storm.
  • The storm in the North Atlantic known as a weather bomb which was a small but potent storm that gains punch as pressure quickly mounts.
  • During the storm, groups of waves had sloshed and pounded the ocean floor which struck between Greenland and Iceland.
  • Using seismic equipment on land and on the seafloor researchers found a tremor known as an S wave microseism.
  • S wave Microseisms are very faint tremors compared to P (primary) wave microseisms and they occur in the 0.05 to 0.5 Hz frequency range.
  • P wave microseisms can be detected easily during major hurricanes. They are fast-moving waves and can travel through gaseous, liquid and solid materials.
  • But the elusive S waves are slower and move only through solid rock, not liquid. Humans feel them during earthquakes.
  • Significance of Discovery: It will help experts learn more about the Earth’s inner structure and improve detection of earthquakes and oceanic storms.
  • Learning more about S waves microseismic will further aid to understand the deeper crust and upper mantle structure.

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Union Government releases Seismic Microzonation reports for Delhi and Kolkata

Union Minister for Science & Technology and Earth Sciences Dr. Harsh Vardhan has released Seismic Microzonation reports for Delhi and Kolkata.

These reports highlight vulnerability of specific areas in these megacities and help in minimizing the effects of earthquakes by (i) Proper assessment of Seismic Hazard (ii) Implementation of safe building construction codes (iii) adopting appropriate land-use planning.

Seismic Microzonation Report for National Capital Territory (NCT) Delhi was prepared by the Earthquake Risk Evaluation Centre (EREC). It was under the IMD and now has been merged with National Centre for Seismology of the Union Ministry of Earth Sciences.

The seismic microzonation project of Kolkata was undertaken by Indian Institute of Technology (IIT) Kharagpur in consortium with a few other organizations under the aegis of the Geosciences Division of the Union Ministry of Earth Sciences.

Benefits of seismic microzonation

  • Disaster Mitigation and Management Authorities.
  • Risk Assessment to existing life & Property especially of Defence Installations, Heavy Industry and Public Utilities and Services.
  • Help Urban Development Authorities and also Planning, Design & Construction Agencies.

Seismic zoning map of India

  • Earlier a seismic zoning map for entire India was prepared and published by the Bureau of Indian Standards (BIS).
  • It had classified the entire country into 4 major groups viz. Zone-V (High intensity), Zone – III (moderate seismic zone), Zone- IV (high seismic zone) and Zone-II (Low intensity).
  • These zones encompass wider area for which specific design spectra is commonly used, despite geo-morphological and geological variability within the respective zone.
  • NCT Delhi was placed in the Seismic zone IV group, whereas Kolkata was placed at the border of Seismic Zone IV and III.

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