Earthquake Swarm in Maharashtra: Causes, Deccan Traps & Seismic Risk

Context:

In recent times, Maharashtra has witnessed a series of small earthquakes over the past fortnight. Around 29 tremors were reported—24 in and around Nashik, four in Palghar and one in Nagpur. Most tremors were shallow, occurring at depths of about 5–8 km. Such a cluster of earthquakes without a clear mainshock is called an earthquake swarm.

What is an Earthquake?

An earthquake is the sudden release of stored energy when rocks move along a fault or zone of weakness in the Earth's crust. This releases seismic waves.

• • • P-waves are compressional waves.
    • S-waves produce sideways shearing.
    • Surface waves travel along the Earth's surface and cause much of the shaking experienced by people.

Unlike a conventional sequence, an earthquake swarm does not have a clearly identifiable mainshock followed by aftershocks.

Why Does Maharashtra Experience Earthquake Swarms?

• • • Intraplate Earthquakes:
      • Maharashtra is located away from major tectonic plate boundaries. Its earthquakes are therefore largely intraplate earthquakes, occurring within the Indian Plate. Although the Indian Plate is relatively stable, it continues to move and deform, allowing tectonic stresses to accumulate within its interior.
    • Deccan Traps and Geological Weaknesses:
      • Much of Maharashtra lies on the Deccan Plateau, whose bedrock consists largely of the Deccan Traps. These basaltic formations were created by massive volcanic eruptions around 66 million years ago.
      • The thick lava layers contain fractures, joints and shear zones. These pre-existing weaknesses can transmit accumulated tectonic stress and become locations for earthquake activity.
    • Role of Water and Rainfall:
      • Rainwater can infiltrate through soil, fractures and permeable rocks. When it reaches deeper cracks connected to faults, it can increase pore-water pressure and reduce friction along fault surfaces.
      • Studies of the Palghar earthquake swarm of 2018 found evidence linking increased seismicity with rainfall and the movement of water into subsurface fractures. However, scientists also identify tectonic stresses, normal faulting and aseismic deformation as possible factors.

Koyna and Reservoir-Induced Seismicity:

Maharashtra also provides a famous example of reservoir-triggered seismicity. After the Koyna reservoir was filled, seismic activity increased in the region. This culminated in the magnitude 6.3 Koyna earthquake of 1967, which caused extensive damage and more than 200 deaths.

Does a Swarm Predict a Major Earthquake?

An earthquake swarm does not automatically indicate that a larger earthquake is imminent. Different swarms have different causes and may continue for varying durations.

Way Forward:

India needs stronger seismic monitoring and early-warning systems to detect earthquake patterns. Seismic microzonation should identify high-risk areas and guide urban planning. Strict implementation of earthquake-resistant building codes is essential, especially in vulnerable regions. Reservoir operations should be closely monitored for induced seismicity. Finally, public awareness, evacuation drills and disaster preparedness must be strengthened to minimise loss of life and property.

Conclusion:

Maharashtra's earthquake swarms demonstrate that significant seismic activity can occur even away from plate boundaries. A combination of tectonic stress, geological fractures, rainfall-induced pore pressure and, locally, reservoir effects can influence seismicity. Continuous scientific monitoring and resilient infrastructure are therefore essential for reducing earthquake risk.