Which of the following is the most damaged MSK IX risk zone in the context of an earthquake?

Question

Prepp Team · Accepted Answer

Understanding Earthquake Risk Zones and the MSK Scale

Earthquakes are a significant natural hazard, and understanding the level of risk in different regions is crucial for preparedness. Seismic zoning maps categorize areas based on their potential for seismic activity. These zones often relate to expected earthquake intensity or magnitude.

The question asks about the "most damaged MSK IX risk zone" in India. This requires understanding the MSK scale and India's seismic zoning.

What is the MSK Scale?

The Medvedev–Sponheuer–Karnik scale, or MSK scale, measures the intensity of ground shaking at a specific location during an earthquake. It describes the effects of an earthquake on people, buildings, and the environment.

The MSK scale has 12 intensity levels, typically denoted by Roman numerals (I to XII). Each level describes increasingly severe effects. MSK IX, specifically, corresponds to a 'Destructive' earthquake. At this intensity level, the shaking is strong enough to cause:

Considerable damage to ordinary substantial buildings (e.g., walls cracking).
Significant damage to weak buildings (e.g., partial collapse).
Cracking of the ground, landslides in susceptible areas.
General panic among people.

An MSK IX risk zone is therefore an area where earthquakes are expected to cause shaking of this destructive intensity.

Seismic Zoning in India

India is divided into seismic zones based on historical earthquake data and tectonic setting. The current seismic zoning map of India (as revised) categorizes the country into four zones: Zone II, Zone III, Zone IV, and Zone V.

Zone V: Highest seismic risk, expecting the highest intensities (often corresponding to MSK IX or higher).
Zone IV: High seismic risk.
Zone III: Moderate seismic risk.
Zone II: Low seismic risk.

The intensity values associated with these zones relate to the maximum intensity expected on scales like the Modified Mercalli Intensity (MMI) scale or the MSK scale. Zone V regions are typically where MSK IX or even higher intensities might be experienced during significant earthquakes.

Identifying the Most Damaged MSK IX Risk Zone

Looking at India's seismic zoning map, the regions falling under Zone V, the highest risk zone, are most likely to experience MSK IX intensity or higher and thus be the "most damaged MSK IX risk zone".

Regions in Zone V include:

The entire North-Eastern India.
Parts of Jammu and Kashmir (now Ladakh and J&K UTs).
Parts of Himachal Pradesh.
Parts of Uttarakhand.
Rann of Kutch in Gujarat.
Northern part of Bihar.
Andaman & Nicobar Islands.

Comparing this with the given options:

Tamil Nadu: Mostly falls in Zone II or III. Not a high-risk zone.
Rajasthan: Mostly falls in Zone II or III. Not a high-risk zone.
North eastern states: The entire region falls under Zone V, making it the highest seismic risk zone in India. This region has experienced numerous large earthquakes capable of causing MSK IX intensity or higher.
Karnataka: Mostly falls in Zone II or III. Not a high-risk zone.

Given that the North eastern states are predominantly classified under Zone V, they represent the region most susceptible to experiencing destructive shaking corresponding to MSK IX intensity during an earthquake, leading to significant damage. Therefore, it is considered the most damaged MSK IX risk zone.

Based on the seismic zoning of India, the North eastern states fall into the highest risk category, aligning with areas expected to experience MSK IX intensity or greater, resulting in the most damage.

Region	Typical Seismic Zone (India)	Expected MSK Intensity Level	Risk Level (MSK IX Context)
Tamil Nadu	Zone II / III	Lower than IX	Lower Risk
Rajasthan	Zone II / III	Lower than IX	Lower Risk
North eastern states	Zone V	IX or Higher Possible	Highest Risk
Karnataka	Zone II / III	Lower than IX	Lower Risk

Revision Table: Key Earthquake Risk Concepts

Concept	Description	Relevance to Question
Earthquake	Shaking of the ground caused by sudden movement of tectonic plates.	Natural hazard causing damage in risk zones.
MSK Scale	Measures earthquake intensity based on observed effects.	MSK IX is a specific level of destructive intensity.
MSK IX Intensity	'Destructive' level, causing significant damage to buildings, ground cracks.	Question focuses on zones prone to this intensity.
Seismic Zoning	Categorizing regions by their potential for seismic hazard/risk.	India is zoned II, III, IV, V based on risk.
Zone V	Highest seismic hazard zone in India. Expected to experience highest intensities (like MSK IX+).	Represents the most damaged risk zone.

Additional Information: Seismic Risk in India

India's high seismic risk in certain regions is due to the collision of the Indian tectonic plate with the Eurasian plate. This ongoing geological process causes significant stress buildup, leading to frequent earthquakes, especially along the Himalayan front and in the North eastern region.

The Bureau of Indian Standards (BIS) is the official agency that publishes the seismic zoning map of India.
The Zone V area covers about 11% of India's landmass.
Zone IV covers about 18%, Zone III about 30%, and Zone II the remaining 41%.
While the question uses the MSK scale, the Modified Mercalli Intensity (MMI) scale is also commonly used to describe earthquake intensity. Both are similar empirical scales.
Understanding these zones helps in implementing appropriate building codes and disaster preparedness measures to mitigate damage during earthquakes.