Earthquake & Seismic Zones — Set 13

Correct Answer: B. Delhi's urban expansion into Zone IV areas and increasing building density increase the city's earthquake risk alongside the ongoing Himalayan seismic threat

Delhi's earthquake risk is compounded by the city's rapid urban expansion into Zone IV seismic areas and the increasing density of construction, including many buildings that do not meet modern seismic codes. As Delhi grows, more people and structures are exposed to the earthquake hazard from the nearby Himalayan seismic zone. NDMA has specifically highlighted Delhi as a priority area for earthquake preparedness and has funded microzonation studies to guide risk reduction planning for the capital.

Correct Answer: B. Elastic waves that travel through the Earth caused by sudden energy release — different types arise from different wave propagation modes

Seismic waves are elastic waves that travel through the Earth's interior and along its surface, generated by sudden energy releases such as earthquakes, explosions, or volcanic activity. Different types arise from different wave propagation modes: P waves (compression), S waves (shear), and surface waves (Love and Rayleigh). Each type travels at different speeds and has different particle motion, allowing seismologists to use the arrival time differences to locate earthquakes and study the Earth's internal structure.

Correct Answer: A. January 26 — Republic Day and Bhuj earthquake anniversary

January 26 holds special significance in India's earthquake preparedness calendar as it is both India's Republic Day and the anniversary of the devastating 2001 Bhuj earthquake. NDMA and state disaster management authorities use this occasion to conduct earthquake drills, mock exercises, and awareness campaigns across earthquake-prone states. The coincidence of the earthquake with Republic Day celebrations has made it a particularly poignant reminder of earthquake preparedness needs.

Correct Answer: B. India's dominant seismicity is continental collision (Indian-Eurasian) rather than oceanic subduction (Japan) or transform faulting (California)

India's dominant seismicity results from continental collision between the Indian and Eurasian plates — a convergent boundary without subduction of oceanic crust. Japan's seismicity is dominated by oceanic subduction (Pacific plate subducting under Eurasian plate), while California's is dominated by transform faulting (Pacific-North American plates sliding past each other). These different tectonic settings produce different earthquake characteristics, with India's continental collision zone capable of generating great earthquakes on the Himalayan thrust faults.

Correct Answer: B. Move to high ground immediately without waiting for a tsunami warning, as strong shaking near coast is its own warning

Communities near coastlines should move to high ground immediately after feeling strong earthquake shaking without waiting for an official tsunami warning. Strong and prolonged earthquake shaking near the coast is itself a natural warning of potential tsunami generation. The 2004 Indian Ocean Tsunami demonstrated that waiting for official warnings can cost lives — people who immediately moved to high ground after feeling the earthquake survived while those who waited on beaches were killed. This 'natural warning' response saves lives when formal warning systems may have insufficient lead time.

Correct Answer: B. Elastic strain energy stored in rocks along fault zones due to ongoing plate tectonic motion — its eventual release causes earthquakes

Tectonic stress accumulation is the buildup of elastic strain energy in rocks along fault zones as tectonic plates continuously move, loading the locked fault with increasing stress. When the accumulated stress exceeds the fault's frictional resistance, it suddenly releases as an earthquake. In India, the ongoing convergence of the Indian and Eurasian plates at 5 cm/year continuously loads the Himalayan thrust faults with stress. Seismologists use geodetic measurements (GPS) to monitor this strain buildup as part of long-term earthquake hazard assessment.

Correct Answer: B. GPS-based measurements of ground deformation that quantify tectonic strain accumulation on Himalayan fault systems

Geodetic measurements using GPS and InSAR (satellite radar) quantify the rate of tectonic strain accumulation on fault systems in the Himalayan region by precisely measuring ground deformation. These measurements show where tectonic stress is building up — identifying locked fault segments that could generate future large earthquakes. Indian research institutions including Survey of India and university research groups maintain GPS networks in the Himalayan region to monitor these strain patterns for long-term earthquake hazard assessment.

Correct Answer: C. Approximately 10,653 people

The 1934 Bihar-Nepal Earthquake killed approximately 10,653 people, with the majority in Bihar and Nepal. The earthquake struck on January 15, 1934 (Makar Sankranti) at 2:13 PM when many people were outside for the festival, which paradoxically may have reduced casualties compared to a nighttime event. The earthquake caused massive liquefaction in the Gangetic Plains and significant damage to the cities of Patna, Muzaffarpur, and the then-capital Darbhanga.

Correct Answer: B. The coupled dynamic response between the building and its foundation soil that modifies earthquake forces

Soil-structure interaction (SSI) refers to the coupled dynamic response between a building and its foundation soil during earthquake shaking — the building modifies the ground motion, and the soil modifies the building's response. For buildings on soft soils, SSI can significantly alter the seismic forces compared to those calculated assuming rigid foundations. IS 1893 accounts for soil-structure interaction effects in the design of heavy, flexible structures on soft soils in earthquake zones.

Correct Answer: B. Conducting geodetic surveys and GPS measurements to monitor ground deformation related to tectonic activity in seismically active regions

The Survey of India conducts geodetic surveys and GPS measurements to monitor ground deformation and tectonic strain in seismically active regions of India. These measurements help quantify the rate of tectonic movement along active fault zones, particularly in the Himalayan region. The Survey of India's geophysical work, combined with NCS seismological data and GSI geological data, provides a comprehensive picture of India's earthquake hazard for NDMA's risk assessment and planning.