Tsunami Case Study and Preparedness

2004 Indian Ocean Tsunami

Background of the Disaster

• Date: 26th December 2004.
• Cause: A megathrust earthquake (9.0 Richter scale) near the western boundary of Sumatra.
• Impact: Triggered a series of massive tsunami waves across the Indian Ocean, causing unprecedented devastation.

👉 This was one of the deadliest natural disasters in modern history.

Plate Tectonics – The Trigger

• The Indian Plate was subducting under the Burma Plate.
• Due to stress buildup, there was a sudden rupture of the sea floor:
  • Ocean floor displaced by 10–20 metres.
  • Tilted downward, creating a massive gap.
• Water rushed in to fill this gap → withdrawal of sea water from the coastlines (classic tsunami sign).
• Then, water mass surged back violently → the tsunami waves.

👉 Mechanism = textbook example of subduction zone tsunami.

Tsunami Waves – The Deadly Journey

• Speed in deep ocean: ~800 kmph (like a jet aircraft!).
• Washed away entire islands in the Indian Ocean.
• Indira Point (southernmost tip of India, Andaman & Nicobar) got submerged permanently.
• As waves moved outward:
  • Wavelength decreased with shallower waters.
  • Speed dropped from 700–900 kmph to less than 70 kmph near coasts.
  • But due to shoaling, wave height increased, causing maximum destruction.
• In India:
  • Tsunami waves penetrated 3 km inland in places.
  • More than 10,000 people killed.
  • Worst-affected: Andhra Pradesh, Tamil Nadu, Kerala, Puducherry, Andaman & Nicobar Islands.

Shifts in Geography

This part is fascinating — the disaster was so massive it altered Earth’s physical parameters:

• Shift of Earth’s axis:
  • North Pole shifted by 2.5 cm towards 145° East longitude.
• Rotation of Earth:
  • Length of the day shortened by 2.68 microseconds.
  • Slight change in Coriolis force, which influences global weather patterns.
• Regional Geography:
  • Andaman & Nicobar Islands shifted ~1.25 m due to tectonic activity.

👉 This shows that earthquakes and tsunamis are not just local events; they can reshape geography at both local and global scales.

Tsunami Warning Systems

The Problem

• Earthquakes (the primary cause of tsunamis) cannot be predicted in advance.
• But — once an earthquake occurs under the sea, the movement of tsunami waves can be tracked.
• This allows a warning window of up to 3 hours before waves hit distant shores.

👉 Hence, tsunami early warning systems are critical.

Global Warning Systems

• The first organised system began in 1965, led by the National Oceanic and Atmospheric Administration (NOAA), USA.
• It covers Pacific Rim countries, since the Pacific Ocean is the most tsunami-prone region.

DART System (Deep Ocean Assessment and Reporting of Tsunamis)

• How it works:
  1. A sensitive pressure recorder is placed on the sea floor.
  2. If water pressure changes (indicating a wave passing), data is generated.
  3. This data goes to a surface buoy.
  4. From there, it is relayed via satellite.
  5. The Pacific Tsunami Warning Centre (PTWC), Hawaii processes the data and issues alerts.

👉 In short: Seafloor gauge → Buoy → Satellite → PTWC → Warnings issued.

India’s Preparedness

After the 2004 Indian Ocean tsunami, India realised the urgency of having its own system.

• DOARS (Deep Ocean Assessment and Reporting System) was set up in the Indian Ocean.
• National Tsunami Early Warning Centre (NTEWC) was inaugurated in 2007 at INCOIS, Hyderabad, under the Ministry of Earth Sciences.

Key features:

• Can detect earthquakes >6 magnitude in the Indian Ocean.
• Takes 10–30 minutes to process seismic data and issue warnings.
• Provides early warnings to India and neighbouring countries.

‘Tsunami Ready’ Programme

• This is a global initiative by UNESCO’s Intergovernmental Oceanographic Commission (IOC).
• Aim: To make coastal communities self-reliant, aware, and prepared for tsunami risks.
• In India, it is implemented by INCOIS.

India’s Role

• INCOIS runs the Indian Tsunami Early Warning Centre (ITEWC).
• ITEWC provides not only tsunami warnings, but also alerts for storm surges and high waves.
• UNESCO-IOC has designated ITEWC as a Regional Tsunami Service Provider (RTSP), meaning:
  • It provides tsunami alerts not just for India, but for all Indian Ocean Rim countries.