Why is peninsular India seismically stable while the Himalayas are highly active, though both belong to the same plate?

Both peninsular India and the Himalaya sit on the Indian plate, yet the peninsula records only occasional moderate tremors while the Himalayan arc has produced several great earthquakes. The difference lies in their position relative to the plate boundary and in the age and rigidity of the crust.

Why the Himalaya is highly active

• It is a collision boundary: The Indian plate is under-thrusting Eurasia at about 45-50 mm per year, and most of that convergence is absorbed along the Main Boundary and Main Central Thrusts.
• Locked-and-release behaviour: Strain accumulates on the shallow, locked Main Himalayan Thrust and is released in great earthquakes, as at Bihar-Nepal (1934), Kangra (1905) and Gorkha (2015).
• Young, weak, fractured crust: Thick sedimentary piles and thrust sheets deform readily instead of resisting stress.

Why the peninsula is comparatively stable

• Ancient shield crust: The Archaean gneisses and granites of the Deccan shield are rigid, cold and mechanically strong.
• Intra-plate position: It lies far from the active margin, so far less strain is transmitted into it.
• Only reactivated old faults: Stress leaks into ancient rift zones, producing infrequent but shallow and destructive events such as Latur (1993), Koyna (1967) and Bhuj (2001).

Belonging to one plate does not mean sharing one seismic regime. The Himalaya is where the plate is being deformed; the peninsula is the rigid interior that mostly transmits stress rather than absorbing it.