Earthquake & Seismic Zones — Set 14

Correct Answer: B. Eastern Himalayas (Zone IV-V) have much higher seismic hazard due to active tectonic collision while Western Ghats (Zone II-III) have lower intraplate hazard

The Eastern Himalayas (Zone IV-V) have much higher seismic hazard because they sit directly on the active tectonic collision zone between the Indian and Eurasian/Burmese plates, where great earthquakes regularly occur. The Western Ghats, being in the stable interior of the Indian plate, fall in Seismic Zones II-III with lower but not negligible hazard. This contrast illustrates how proximity to active plate boundaries fundamentally determines earthquake risk in India's diverse geological landscape.

Correct Answer: B. Aftershocks are generally smaller than the mainshock but can still cause additional damage to already weakened structures — buildings should be inspected before re-entry

After a major earthquake, the general rule is that aftershocks are smaller than the mainshock (usually 1-1.5 magnitude units less) but can still cause additional collapse of buildings already damaged by the mainshock. The Bath's Law states the largest aftershock is typically 1.2 magnitude units below the mainshock. NDMA's guidelines recommend that building inspections be conducted before residents re-enter damaged structures to assess their safety for aftershock loading.

Correct Answer: B. Widespread non-compliance, lack of qualified engineers in smaller towns, corruption, and inadequate inspection systems

Building code enforcement for earthquake safety in India faces multiple challenges: widespread non-compliance especially in small and medium cities and rural areas; shortage of qualified structural engineers to design and inspect buildings in smaller towns; inadequate inspection systems and corruption in approval processes; lack of community awareness about building standards; and cost constraints for low-income builders. These systemic challenges mean that many new buildings continue to be constructed without adequate seismic provisions, perpetuating India's earthquake vulnerability.

Correct Answer: B. Magnitude 5.8 earthquake that killed 38 people, demonstrating earthquake hazard in central India's Zone III areas and near the Narmada Son Lineament

The 1997 Jabalpur Earthquake (magnitude 5.8) in Madhya Pradesh killed 38 people and caused significant building damage, demonstrating the earthquake hazard in central India along the Narmada-Son Lineament — an ancient tectonic zone cutting across central India. This intraplate earthquake in a Zone III area highlighted that even areas with moderate seismic hazard classification can experience damaging earthquakes, similar to the lesson from the 1993 Latur earthquake in Maharashtra.

Correct Answer: B. ISRO's satellites provide before-after imagery for rapid damage assessment, infrastructure mapping, and landslide monitoring after earthquakes

India uses ISRO's satellite constellation (including Resourcesat, Cartosat, and RISAT) to provide before-and-after optical and radar imagery for rapid post-earthquake damage assessment. ISRO's Disaster Management Support (DMS) programme specifically activates when major earthquakes occur to provide satellite data to NDMA and state agencies. This information helps identify the extent and severity of building damage, blocked roads and infrastructure failures, and landslide occurrences to guide rescue and relief operations.

Correct Answer: B. Natural seismicity results from tectonic processes while induced seismicity is triggered by human activities like reservoir filling, mining, or fluid injection

Natural seismicity results from natural tectonic processes — plate movement, fault rupture, and volcanic activity. Induced (man-made) seismicity is triggered by human activities including reservoir impoundment (Koyna Dam), deep mining, underground fluid injection (fracking, wastewater disposal), and large-scale groundwater extraction. India has experienced significant induced seismicity at the Koyna Dam and in mining areas of Jharkhand and Assam. Understanding induced seismicity is increasingly important as India expands its infrastructure development.

Correct Answer: B. Detailed neighborhood-level hazard mapping showing how ground conditions affect shaking at spatial scales relevant for city planning and building regulation

Seismic microzonation at 1:10,000 scale means detailed mapping of local site conditions at the neighborhood level, showing spatial variations in ground shaking potential at scales relevant for city planning and building regulation. At this scale, planners can identify specific blocks and neighborhoods with high liquefaction potential, soft soil amplification, or slope instability, and apply appropriate building regulations or land use restrictions. NDMA has funded 1:10,000 scale microzonation studies for several Indian cities including Delhi, Bangalore, Jabalpur, and Guwahati.

Correct Answer: C. Every 200-700 years based on paleoseismological evidence

Paleoseismological studies along the Main Himalayan Thrust indicate that great earthquakes (magnitude 8 or larger) have recurrence intervals of approximately 200-700 years in different segments of the Himalayan arc. The Himalayan Frontal Thrust appears to have experienced great earthquake ruptures at recurrence intervals of 400-600 years in some segments. This means some segments may be 'due' for a great earthquake, given that the last known great earthquake in certain areas was hundreds of years ago.

Correct Answer: B. Seismic retrofitting techniques — adding reinforced concrete jacketing, shear walls, base isolation, or steel bracing

Seismic retrofitting is the primary engineering technique used to improve the earthquake resistance of existing buildings in India without complete demolition. Common techniques include: adding reinforced concrete jackets around existing columns, adding new shear walls, installing steel bracing frames, using base isolation for critical facilities, and applying fiber-reinforced polymer (FRP) wrapping to columns and beams. NDMA's guidelines provide prioritization frameworks for retrofit programs, recommending that critical facilities like hospitals and schools be prioritized.

Correct Answer: B. A combination of improved building codes, enforcement, community preparedness, early warning systems, and trained response forces is essential to reduce India's earthquake risk

India's earthquake history — from Kangra 1905 to Bhuj 2001 to Sikkim 2011 — teaches that reducing earthquake risk requires a comprehensive, multi-pronged approach: enforcing earthquake-resistant building codes, retrofitting critical facilities, training NDRF and community first responders, developing early warning systems, and conducting public awareness campaigns. No single measure is sufficient on its own. NDMA's earthquake preparedness framework integrates all these elements to progressively reduce India's high earthquake vulnerability even as the underlying tectonic hazard remains constant.