Knowledge Nugget | 25 years of Bhuj earthquake: What you must know for UPSC Exam?

Key Takeaways:

1. Gujarat’s historic earthquake, measuring 6.9 on the Richter scale, killed over 20,000 people, injuring 166,000 and destroying nearly 400,000 homes. The shock waves spread over 700 km; 21 districts were affected, and 600,000 people were left homeless. Bhuj was the epicenter of the earthquake. 

2. The Bhuj earthquake was a turning point that moved India’s disaster response from reactive relief to a proactive, institutionalised system, forming the basis of today’s disaster management framework.

Widespread destruction after the Bhuj earthquake. (Express Archive Photo)

3. While many believed that Gujarat would take years to get back to normal, the massive rehabilitation and reconstruction undertaken brought a resilient Gujarat back from the rubble.

What is an earthquake?

1. An earthquake is an intense shaking of the ground caused by movement under the earth’s surface. It happens when two blocks of the earth suddenly slip past one another, according to USGS. This releases stored-up ‘elastic strain’ energy in the form of seismic waves, which spreads through the earth and cause the shaking of the ground.

2. The earth’s outermost surface, crust, is fragmented into tectonic plates. The edges of the plates are called plate boundaries, which are made up of faults. The tectonic plates constantly move at a slow pace, sliding past one another and bumping into each other. As the edges of the plates are quite rough, they get stuck with one another while the rest of the plate keeps moving. Earthquake occurs when the plate has moved far enough and the edges unstick on one of the faults.

3. The location below the earth’s surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the earth is called the epicentre.

Earthquake Waves

1. When an earthquake occurs, it generates seismic waves that cause the shaking we experience. There are two major types of seismic waves: body waves and surface waves.

2. Body waves comprise P and S waves, and they are called body waves because they can travel through the Earth’s interior, rather than being confined near the surface.

3. Primary or ‘P’ wave is a type of sound wave that travels through rock. In a P wave, the rock particles are alternately compressed and expanded, a process known as compressions and dilatations. This is why P waves are also referred to as compressional waves. They are capable of traveling through solids, liquids, and gases. Notably, P waves can move through the liquid outer core of the Earth.

4. In Secondary or ‘S’ wave, the rock particles slide past one another, which creates shear – hence, S waves are also known as shear waves. S waves cannot travel through liquids or gases, which means they do not propagate through the ocean or the outer core.

5. Surface waves are named for their tendency to be confined near the Earth’s surface, as opposed to traveling through the Earth’s interior like P and S waves. There are two main types of surface waves: Love waves, which are shear waves that are trapped near the surface, and Rayleigh waves, which exhibit particle motions similar to those of water particles in ocean waves.

India’s Vulnerability to Earthquakes

1. India’s vulnerability to earthquakes stems from its geographical position at the convergence of multiple tectonic plates, its intricate geological structure, and a rapidly growing population paired with widespread unregulated construction practices.

2. As a result, the nation is particularly vulnerable to seismic activity. It is ranked as the seventh most earthquake-prone country in the world. 

3. According to ndma.gov.in, approximately 59 per cent of India’s land area is at risk of experiencing moderate to severe seismic events, capable of registering an intensity of VII on the MSK scale or higher.

BEYOND THE NUGGET: National Disaster Management Authority (NDMA)

1. The National Disaster Management Authority is the apex body for Disaster Management in India.

2. Setting up of NDMA and the creation of an enabling environment for institutional mechanisms at the State and District levels is mandated by the Disaster Management Act, 2005.

3. NDMA is mandated to lay down the policies, plans and guidelines for Disaster Management. The Prime Minister is its chairperson and it has nine other members. One of the nine members is designated as Vice-Chairperson.

4. Disaster Management Act also envisaged the creation of State Disaster Management Authorities (SDMAs) headed by respective Chief Ministers and the District Disaster Management Authorities (DDMA) headed by the District Collectors/ District Magistrate and co-chaired by Chairpersons of the local bodies.

5. The primary responsibility for the management of disaster rests with the State Government concerned. However, the National Policy on Disaster Management puts in place an enabling environment for all i.e., the Centre, state and district.

6. India is also a signatory to the Sendai Framework for Disaster Risk Reduction (SFDRR) that sets targets for disaster management.

Post Read Question

Consider the following statements with respect to earthquake: 

1. Primary waves are capable of traveling through solids, liquids, and gases. 

2. Secondary  waves cannot travel through liquids or gases.

3. The location below the earth’s surface where the earthquake starts is called the hypocenter.

How many of the statements given above are correct?

(a) One only

(b) Two only

(c) All three

(d) None

(Sources: ndma.gov.in,  Knowledge nugget of the day: Earthquakes—Why is the Himalayan zone seismically active?)

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