Earthquake & Seismic Zones — Set 5

Correct Answer: B. Logarithmic — each unit increase means 31.6 times more energy released

The relationship between earthquake magnitude and energy release is logarithmic — each whole number increase in magnitude represents approximately 31.6 times more energy released. This means a magnitude 7.0 earthquake releases about 31.6 times more energy than a magnitude 6.0 earthquake, and a magnitude 8.0 releases about 1,000 times more energy than a magnitude 6.0. This exponential relationship explains why large earthquakes are so much more destructive than smaller ones.

Correct Answer: B. NCS monitors seismicity and reports earthquake parameters; IMD issues tsunami warnings for Bay of Bengal cyclones

The National Centre for Seismology (NCS) under the Ministry of Earth Sciences is the primary agency for monitoring seismic activity and reporting earthquake parameters (location, magnitude, depth). The Indian Meteorological Department (IMD) has a separate but complementary role including operating the Indian Tsunami Early Warning Centre (ITEWC) for tsunami alerts. Together these agencies provide the scientific foundation for earthquake and tsunami disaster preparedness.

Correct Answer: B. Maximum acceleration of ground during earthquake shaking — key for designing buildings and structures

Peak Ground Acceleration (PGA) is the maximum acceleration experienced by the ground during earthquake shaking, measured in units of g (gravitational acceleration) or cm/s². It is the key parameter used in earthquake engineering to determine the forces that buildings and structures must withstand. IS 1893 specifies PGA values for different seismic zones in India, and buildings must be designed to resist these forces to ensure earthquake safety.

Correct Answer: B. Securing heavy furniture, having emergency kits, knowing safe spots and exit routes

Earthquake preparedness at the household level includes multiple measures: securing heavy furniture and appliances to walls to prevent toppling, maintaining an emergency kit with essentials, knowing the 'drop, cover, and hold on' procedure, identifying safe spots in each room, practicing evacuation routes, and storing important documents safely. NDMA's earthquake preparedness guidelines emphasize these household-level measures alongside community and government preparedness.

Correct Answer: B. Drop to floor, take cover under sturdy furniture or against interior wall, hold on until shaking stops

The 'Drop, Cover, and Hold On' (DCHO) procedure is the internationally recommended action during earthquake shaking: Drop to hands and knees to prevent being knocked down, take Cover under a sturdy desk, table, or against an interior wall to protect the head and neck, and Hold On until the shaking completely stops. This replaces older guidance to stand in doorframes, which research shows offers no special protection. NDMA promotes this procedure in its earthquake preparedness campaigns.

Correct Answer: B. Traditional stone construction (wada) that collapsed completely in early morning hours when people were sleeping

The unusually high death toll in the 1993 Latur Earthquake (approximately 9,748 people) despite its moderate 6.2 magnitude was primarily due to the traditional stone construction (wada) prevalent in the region that collapsed completely. The earthquake struck at 3:56 AM when most people were sleeping in these poorly constructed stone houses. The unconfined masonry construction with heavy stone roofs proved catastrophically lethal, killing thousands who had no chance of escape.

Correct Answer: B. Reservoir-induced seismicity from Koyna Dam — among the world's largest reservoir-triggered earthquakes

The Koyna earthquake series in Maharashtra represents reservoir-induced seismicity (also called triggered seismicity) caused by the impoundment of the Koyna Dam reservoir. The most significant event, a 6.5 magnitude earthquake in 1967, killed 177 people and is one of the world's largest reservoir-triggered earthquakes. The Koyna area continues to experience frequent earthquakes due to the reservoir's influence on the local stress field, making it one of the most studied examples of reservoir-induced seismicity globally.

Correct Answer: B. It identifies unruptured fault segments that have accumulated stress for over 200-500 years and may generate future great earthquakes

The Himalayan seismic gap identifies segments of the Main Himalayan Thrust where no major earthquake has occurred for several centuries, suggesting accumulated tectonic stress that could be released in future great earthquakes. Seismologists have identified a major seismic gap in Uttarakhand and western Nepal that has not experienced a great earthquake since 1505. The occurrence of such a great earthquake could be catastrophic for densely populated Himalayan cities and the Gangetic plains below.

Correct Answer: C. Kutch district, particularly Bhuj and Anjar towns

The 2001 Bhuj Earthquake caused the most severe damage in the Kutch district, particularly in the town of Bhuj (near the epicentre) and Anjar town which was almost completely destroyed. While Ahmedabad (300 km away) also suffered significant damage due to building collapses in multi-storey apartments, the death toll was concentrated in the Kutch district. The disaster led to a massive reconstruction program in Kutch that incorporated earthquake-resistant construction standards.

Correct Answer: B. It provides earthquake-resistant design and construction of buildings code complementing IS 1893

IS 4326 is the Bureau of Indian Standards code that provides guidelines for earthquake-resistant design and construction of buildings, complementing the design requirements in IS 1893. While IS 1893 specifies the seismic forces that buildings must withstand, IS 4326 provides detailed construction guidelines for different building materials (masonry, reinforced concrete, timber) to ensure earthquake resistance. Together these codes form the basis of India's earthquake-resistant building standards.