SSC
The magnitude of the earthquake that caused the Indian Ocean tsunami of 26 December 2004 was about:
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Answer: Option D — 9.1
Detailed Solution
The Indian Ocean earthquake of 26 December 2004 had a moment magnitude of about 9.1 to 9.3, making it one of the strongest earthquakes ever recorded. It is commonly given as 9.1.
About the earthquake:
It struck at about 7:59 a.m. local time (about 6:28 a.m. IST) off the west coast of northern Sumatra, Indonesia.
It was caused by a rupture along the boundary where the India Plate slides beneath the Burma microplate (part of the Eurasian Plate), in a "subduction zone".
The rupture was about 1,300-1,600 km long, one of the longest ever recorded, and the sea floor was lifted by several metres.
It is the third-largest earthquake recorded since 1900, after the Chile earthquake of 1960 (magnitude 9.5, the strongest ever recorded) and the Alaska earthquake of 1964 (9.2).
It lasted about 8-10 minutes, the longest duration ever observed.
The tsunami:
- It sent huge tsunami waves, up to 30 metres high, across the Indian Ocean.
- About 2,30,000 people were killed in 14 countries, making it one of the deadliest natural disasters in history.
- Indonesia (especially Aceh province) was the worst affected, followed by Sri Lanka, India and Thailand.
- In India, more than 10,000 people died, mainly in Tamil Nadu (especially Nagapattinam), the Andaman and Nicobar Islands, Kerala, Andhra Pradesh and Puducherry.
- The waves reached as far as Somalia and Kenya in East Africa.
After the disaster:
- There was no tsunami warning system in the Indian Ocean in 2004.
- The "Indian Ocean Tsunami Warning and Mitigation System" was set up under UNESCO's Intergovernmental Oceanographic Commission and became operational in 2011.
- India set up the "Indian Tsunami Early Warning Centre" (ITEWC) at INCOIS, Hyderabad, in October 2007.
- India's Disaster Management Act was passed in 2005, and the National Disaster Management Authority (NDMA) was set up.
- World Tsunami Awareness Day is observed on 5 November (since 2016).
About measuring earthquakes:
The "moment magnitude scale" is now used for large earthquakes. The older Richter scale was developed by Charles Richter in 1935.
Each whole number increase in magnitude means about 32 times more energy released.
Why not the other options?
- ✗7.5 is far too small for an earthquake of this size.
- ✗8.2 is also too small.
- ✗9.8 is larger than any earthquake ever recorded.
Quick tip
Remember: 2004 Indian Ocean earthquake = magnitude about 9.1 (26 December 2004; off Sumatra; about 2,30,000 deaths); strongest recorded = Chile 1960 (9.5); India's tsunami warning centre = INCOIS, Hyderabad (2007).
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This question tests your understanding of Earth: Structure, Rocks & Landforms, a key topic in the General Knowledge section. The detailed solution above uses a step-by-step approach to show the reasoning, and where available, a shortcut that helps you solve similar questions in under 90 seconds during the actual exam.
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