Earthquake & Seismic Zones — Set 9

Correct Answer: B. Delhi — with microzonation maps of Delhi city developed by NDMA and IIT Delhi

Delhi has developed detailed earthquake microzonation maps through collaborative research by NDMA, IIT Delhi, and other institutions. Microzonation involves detailed mapping of local site conditions (soil type, depth, geology) that affect ground shaking at the neighborhood level within a city. Delhi's microzonation maps help urban planners and engineers identify the specific areas most vulnerable to earthquake amplification for targeted risk reduction measures.

Correct Answer: B. USGS provides rapid global earthquake location data that supplements India's NCS data, especially for very large earthquakes

The USGS National Earthquake Information Center (NEIC) provides rapid global earthquake location data within minutes of significant earthquakes worldwide, which supplements India's NCS data especially for very large earthquakes where prompt international comparison helps confirm parameters. The USGS PAGER (Prompt Assessment of Global Earthquakes for Response) system provides rapid fatality and loss estimates that assist India's disaster management agencies in resource mobilization. This international data sharing is part of global earthquake monitoring cooperation.

Correct Answer: B. 6.8 magnitude — significant damage to buildings and triggering landslides in the Himalayan region

The 1999 Chamoli Earthquake struck Uttarakhand (then part of Uttar Pradesh) on March 29, 1999 with a magnitude of 6.8. It killed approximately 100 people and caused significant damage to buildings, infrastructure, and triggered numerous landslides in the Himalayan terrain. This earthquake, occurring in the same Himalayan zone as the 1905 Kangra and the Bhuj events, highlighted the continuous seismic threat to the region.

Correct Answer: C. About 60%

The correct answer is 'About 60%'. Approximately 60% of India's population lives in Seismic Zones III, IV, and V — areas with moderate to very high earthquake hazard. This large earthquake-exposed population makes earthquake risk management a critical national priority. The vulnerability is compounded by the fact that many homes and buildings in these zones are not constructed according to earthquake-resistant standards, especially in rural areas.

Correct Answer: B. Study of prehistoric earthquakes through geological evidence to understand recurrence patterns of large earthquakes

Palaeoseismology is the scientific study of prehistoric earthquakes through geological evidence such as offset layers in trenches dug across fault zones, displaced landforms, and earthquake-triggered sediment liquefaction features. In India, palaeoseismological studies along the Himalayan thrust faults have revealed evidence of multiple great earthquakes over the past 1,000-5,000 years that predate written records. These studies help estimate recurrence intervals and maximum possible magnitudes for future earthquakes.

Correct Answer: C. Koyna Dam (Maharashtra)

The Koyna Dam in Maharashtra has been significantly affected by reservoir-induced seismicity since its construction in the 1960s. The 1967 Koyna earthquake (magnitude 6.5) was one of the largest known examples of reservoir-triggered seismicity worldwide, killing 177 people and damaging the dam. The Koyna area continues to experience frequent earthquakes today, making it one of the world's most intensively studied sites for reservoir-induced seismicity.

Correct Answer: B. Saturated sandy soil loses strength and acts like quicksand, causing buildings to sink, tilt or topple

During earthquake shaking, liquefaction causes water-saturated sandy soil to lose its strength and behave like quicksand, dramatically reducing its ability to support building foundations. Buildings may sink into the ground, tilt to one side, or lose their foundation support entirely and topple over. The 1934 Bihar earthquake caused widespread liquefaction in the Gangetic plains where entire villages sank into the ground. Proper foundation design and ground improvement techniques can mitigate liquefaction risk.

Correct Answer: B. Vulnerability refers to susceptibility to damage — India has high vulnerability due to old building stock and poor construction, compounding physical hazard

Earthquake vulnerability refers to the susceptibility of buildings, infrastructure, and communities to damage from earthquake ground shaking. India's earthquake vulnerability is compounded by factors including: large amounts of old, unreinforced masonry construction in seismic zones, poor construction quality even for newer buildings, high population densities in hazard-prone areas, and insufficient enforcement of building codes. This high vulnerability means India's earthquake risk (combination of hazard, exposure, and vulnerability) is among the highest in the world.

Correct Answer: B. Ductile detailing of reinforced concrete structures for seismic resistance

IS 13920 is the Bureau of Indian Standards code for ductile detailing of reinforced concrete structures subjected to seismic forces. It specifies the special reinforcement detailing requirements (stirrup spacing, lap lengths, anchorage details) in columns, beams, and joints that ensure ductile behavior during earthquakes. Ductile structures absorb earthquake energy through controlled deformation, preventing sudden brittle collapse and protecting human lives.

Correct Answer: B. The 1950 earthquake occurred in a sparsely populated remote area while Bhuj occurred in a populated urban area

The 1950 Assam earthquake (8.6 magnitude) caused approximately 1,526 direct deaths while the 2001 Bhuj earthquake (7.7 magnitude) caused approximately 20,000 deaths. The key difference is population exposure — the 1950 earthquake struck the sparsely populated remote Himalayan region near the China border while the 2001 Bhuj earthquake struck the populated Kutch district with its towns and villages. This demonstrates that earthquake risk depends on both the hazard and the population and building exposure.