Differentiate between the 'intensity' and 'magnitude' of an earthquake and explain its varying impact in different parts of India.

Differentiating Intensity and Magnitude

While often used interchangeably, ‘intensity’ and ‘magnitude’ represent distinct aspects of an earthquake.

• Magnitude: This is a quantitative measure of the energy released at the earthquake’s source (hypocenter). It is typically measured using the Richter scale (though the Moment Magnitude Scale is now preferred for larger earthquakes). It’s a single value for each earthquake.
• Intensity: This is a qualitative measure of the shaking felt at a specific location. It depends on factors like magnitude, distance from the epicenter, local geological conditions, and building construction. Intensity is assessed using scales like the Modified Mercalli Intensity Scale, which assigns Roman numerals (I to XII) based on observed effects.

Therefore, magnitude describes the *size* of the earthquake, while intensity describes its *effects* at a given place.

Varying Impact of Earthquakes in Different Parts of India

India’s diverse geological landscape and varying levels of preparedness lead to significantly different earthquake impacts across its regions.

1. Himalayan Region (Seismic Zone V)

This region, including states like Jammu & Kashmir, Himachal Pradesh, Uttarakhand, Sikkim, and parts of Arunachal Pradesh, is the most seismically active due to the ongoing collision of the Indian and Eurasian plates.

• Geology: Highly fractured and unstable geological formations amplify seismic waves.
• Building Construction: Traditional construction methods, often using stone and wood, are vulnerable to collapse.
• Impact: High intensity earthquakes are frequent, leading to widespread damage and landslides. The 2015 Nepal earthquake had significant repercussions in bordering Indian states.

2. Indo-Gangetic Plain (Seismic Zone III & IV)

This densely populated region, encompassing states like Punjab, Haryana, Uttar Pradesh, and Bihar, is susceptible to moderate to high-intensity earthquakes.

• Geology: Alluvial soil amplifies seismic waves, increasing the risk of liquefaction and ground failure.
• Building Construction: Multi-story buildings constructed without adhering to seismic-resistant building codes are particularly vulnerable.
• Impact: High population density exacerbates the impact, leading to a large number of casualties. The 1934 Bihar earthquake (8.0 magnitude) caused widespread devastation.

3. Peninsular India (Seismic Zone II & III)

States like Maharashtra, Gujarat, Karnataka, Tamil Nadu, and Andhra Pradesh experience relatively fewer earthquakes compared to the Himalayan region, but are still vulnerable.

• Geology: Stable, ancient crystalline rocks generally reduce seismic wave amplification. However, intraplate faults exist.
• Building Construction: Modern construction practices are more common, but older buildings may lack seismic resistance.
• Impact: Earthquakes in this region, while less frequent, can still cause significant damage due to high population density and industrial infrastructure. The 2001 Gujarat earthquake (7.7 magnitude) demonstrated the vulnerability of even relatively stable regions.

4. Coastal Regions (Seismic Zone III & IV)

Coastal areas are vulnerable to tsunamis triggered by underwater earthquakes, in addition to the direct effects of ground shaking.

• Geology: Sedimentary deposits and proximity to the sea increase the risk of liquefaction and tsunami inundation.
• Impact: The 2004 Indian Ocean tsunami highlighted the vulnerability of coastal communities.

Region	Seismic Zone	Geological Characteristics	Building Vulnerability	Typical Impact
Himalayan Region	V	Fractured, unstable	Traditional, vulnerable	High intensity, landslides
Indo-Gangetic Plain	III-IV	Alluvial soil, liquefaction risk	Non-seismic resistant buildings	Widespread damage, high casualties
Peninsular India	II-III	Stable crystalline rocks	Variable, older buildings vulnerable	Localized damage, infrastructure disruption