Mains Practice Questions

Introduction

Earthquake swarms are sequences of small to moderate quakes occurring in quick succession, without a distinct mainshock.

• Unlike typical earthquakes, which follow a mainshock-aftershock pattern, swarms consist of multiple quakes of similar magnitude.

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Causes of Earthquake Swarms:

• Fluid Movement: Fluids released from magma or circulating within active geothermal systems can lubricate faults, triggering earthquakes.
  • These fluids move through cracks and fractures, causing multiple small-scale seismic events.
• Active Volcanism: Magma movement beneath the surface creates stress, leading to fracturing of the crust and swarm-like activity.
  • Earthquakes in such cases typically occur near the crack tip where magma is pushing through.
• Slow-Slip Events:
  • These are slow-motion earthquakes involving gradual fault movement over weeks or years.
  • They are commonly observed in subduction zones, such as the Hikurangi Subduction Zone near New Zealand.

Examples of Earthquake Swarms:

• India: Since November 2018, an earthquake swarm has been observed in Dahanu, Maharashtra, with 10–20 quakes daily, typically of magnitude <3.5.
• Philippines: A swarm occurred in Batangas (April–August 2017).
• Europe: The Western Bohemia/Vogtland region (Czechia-Germany) experiences recurrent swarms.
• Central America: In El Salvador (April 2017), nearly 500 earthquakes were recorded in two days in Antiguo Cuscatlán.

Key Differences Between Earthquake Swarms and Mainshock-Aftershock Sequences

Conclusion

Despite their smaller magnitude, the frequency and unpredictability of earthquake swarms can pose significant risks. Therefore, focused monitoring and timely adaptive measures, such as early warning systems and seismic preparedness, are crucial for minimizing potential damage and ensuring public safety in areas prone to swarming seismic activity.