Introduction
Intraplate seismicity refers to earthquakes occurring within the stable interior of a tectonic plate, far from active plate boundaries. Recent earthquake swarms in regions like Nashik and Dindori challenge the traditional perception of Peninsular India as a rigid, completely aseismic landmass, demonstrating that stable continental regions can accumulate and release significant tectonic strain.
Geological Factors Responsible for Intraplate Seismicity
Several distinct geodynamic and structural mechanisms trigger seismic activity in the interior of the Indian plate:
- Far-Field Tectonic Stress: The ongoing northward collision of the Indian Plate with the Eurasian Plate generates intense compressional stress. This flexural buckling of the continental lithosphere transmits stress thousands of kilometres into the continental interior, resulting in periodic stress release.
- Reactivation of Ancient Faults: The Peninsular shield is a heterogeneous mosaic cross-cut by Precambrian rift basins and shear zones, most notably the Son-Narmada-Tapti (SONATA) lineament. When cumulative horizontal tectonic stresses exceed the frictional strength of rocks, these dormant paleo-faults rupture, as seen in the 1993 Latur and 2001 Bhuj earthquakes.
- Subsurface Volcanic and Crustal Weaknesses: The Deccan Volcanic Province (DVP), which covers regions such as Nashik and Palghar, conceals deeply buried pre-volcanic faults and dense mafic dyke swarms. These structural discontinuities serve as localized zones of crustal weakness susceptible to sudden brittle failure.
- Hydro-seismicity and Pore-Fluid Pressure: High percolation of rainwater during the monsoon elevates subsurface hydrostatic and pore-fluid pressures. This fluid migration lubricates shallow fractures, reducing effective normal stress and triggering low-magnitude earthquake swarms, as recurrently observed in Palghar and Nashik.
- Reservoir-Induced Seismicity (RIS): Anthropogenic loading from massive artificial water reservoirs alters pore-fluid conditions and crustal loading on underlying faults, famously instigating the 1967 Koyna earthquake (M 6.3).
Conclusion
Although intraplate earthquakes in Peninsular India are typically shallow and episodic, their localized impact can be catastrophic due to dense populations and historically lower seismic design standards. Strengthening seismic micro-zonation by the National Centre for Seismology (NCS) and rigorously enforcing Bureau of Indian Standards seismic codes (IS 1893) remain essential for regional disaster resilience.