HOW DID THE MYANMAR EARTHQUAKE OCCUR?

THE CONTEXT: A powerful earthquake (magnitude 7.7) struck central Myanmar on March 28, 2025, about 20 km from Mandalay, the country’s second-largest city. The quake was followed by multiple strong aftershocks, including one of magnitude 6.4 just 11 minutes later. This event has caused severe loss of life and infrastructure damage, underscoring South Asia’s tectonic vulnerability.

HISTORICAL PRECEDENTS AND PATTERNS:

1. Past Major Earthquakes

• • 1792: A great ‘megathrust’ earthquake of magnitude 8.5 along Myanmar’s Arakan coast, generating a tsunami in the northern Bay of Bengal.
  • 1839 (Ava earthquake): Estimated magnitude of 7.8, causing over 500 casualties in central Myanmar.
  • 1927: Felt strongly north of Yangon.
  • 1946: Magnitude 7.7 quake possibly on the Sagaing fault north of Mandalay.
  • 2016: A damaging earthquake that struck the historic city of Bagan.

 

2. Rupture Segments

• • Historical data indicate that about half of the Sagaing fault has ruptured over the last few decades.
  • The 2025 Mandalay earthquake continues this sequence of releasing accumulated tectonic stresses.

GEOGRAPHICAL AND TECTONIC CONTEXT:

1. Location and Fault Systems

• • Mandalay lies on the east bank of the Irrawaddy river, near the Sagaing fault (one of the most active regional faults).
  • The Sagaing fault:
    • Runs north-south for approximately 1,400 km, from the Andaman Sea in the south to the eastern Himalayan bend in the north.
    • Accommodates significant strike-slip motion (horizontal displacement) resulting from oblique plate convergence between the Indian and Eurasian Plates.

 

2. Regional Tectonics in South Asia

• • Collision of Indian and Eurasian Plates over ~40 million years: Created major tectonic features (Himalayas, Indo-Burman Range, Andaman-Nicobar subduction zone).
  • The region hosts some of the world’s largest earthquakes, e.g., the 2004 Indian Ocean earthquake (magnitude 9.2).
  • Strain partitioning in Southeast Asia leads to both thrust and strike-slip faulting, making it a “tectonic museum” with earthquakes of varying magnitudes and depths.

 

3. Burma Micro-Plate (Burma Sliver)

• • Lies between the Indian Plate and the Sagaing fault.
  • Formed due to oblique plate convergence, causing deformation to be shared between subduction and strike-slip faulting.
  • The Sagaing fault accommodates about 50-55% of the overall plate motion.

DETAILS OF THE 2025 MANDALAY EARTHQUAKE

1. Magnitude and Depth

• • Main shock: Magnitude 7.7 at ~12:50 pm local time.
  • Shallow focal depth of about 10 km, exacerbating surface damage.
  • Aftershocks: Included a magnitude 6.4 event just 11 minutes later.

 

2. Extent of the Damage

• • Devastation primarily in and around Mandalay, population ~1.5 million.
  • Structures including pagodas, mosques, and bridges either collapsed or were extensively damaged.
  • Southern segments of the Sagaing fault, with thicker Irrawaddy alluvial deposits, saw amplified shaking.
  • Northern regions (including southwest China’s Yunnan Province) largely escaped damage due to structural and wave-propagation factors.

 

3. Effects Beyond Myanmar

• • Bangkok (~1,000 km away) experienced minor but high-profile incidents:
    • Collapse of a 33-storey building under construction.
    • Seismic seiches in a rooftop swimming pool, causing water to overflow.
  • The “long-period waves” traveling far from the epicenter caused upper floors in tall buildings to sway significantly.

 

4. Casualties and Predictions

• • U.S. Geological Survey damage models indicated a potential death toll of 10,000+.
  • Ongoing civil war in Myanmar has complicated rescue and rehabilitation efforts.

GEODYNAMICS OF THE SAGAING FAULT

1. Transform (Strike-Slip) Nature

• • Movement is primarily horizontal, with blocks sliding past each other.
  • Contrasts with thrust fault zones where one block is pushed over the other.
  • Similar to the San Andreas fault system in the western U.S.

 

2. Ridge-Trench Transform Setting

• • The fault links a spreading center under the Andaman Sea with the subduction zone along the Indo-Eurasian plate boundary.
  • Slip rate estimated at 15-25 mm/year, with a cumulative displacement of 100-700 km.

 

3. Earthquake Depth Range

• • Strike-slip quakes typically originate at shallower depths (10-15 km).
  • Thrust fault earthquakes in the region can occur up to 400 km deep, especially under the Indo-Burmese Arc and Indonesian sector.

REASONS FOR VARIABLE DAMAGE PATTERNS:

1. Local Geology and Sediment Thickness

• • Irrawaddy river alluvium amplifies seismic waves, explaining high destruction in southern parts of the fault zone.
  • Thinner sediment cover and different rock properties further north and west reduce shaking intensity.

 

2. Direction of Energy Release

• • Earthquake energy traveled predominantly north-south along the fault.
  • Eastern parts of India and southwest China experienced less shaking due to wave propagation patterns.

 

3. Shallow Depth of Rupture

• • The quake source at 10 km depth contributes to strong ground shaking, large felt area, and structural damage.

IMPLICATIONS FOR INDIA AND WIDER SOUTH ASIA

1. High Seismic Risk Region

• • India is among the world’s most earthquake-prone countries due to the Himalayan collision zone, Indo-Burmese arc, and other active fault systems.
  • The 2025 quake in Myanmar highlights the need for robust earthquake preparedness across the subcontinent.

 

2. Mitigation Strategies

• • Adoption of scientifically tested seismic safety measures, especially in megacities.
  • Retrofit vulnerable structures, enforce strict building codes, and ensure disaster response readiness.
  • Invest in earthquake hazard research and early-warning systems.

 

3. Shared Tectonic Environment

• • Ongoing plate convergence affects multiple countries in South and Southeast Asia.
  • Collaborative geophysical research and regional cooperation can strengthen resilience against future seismic events.

THE CONCLUSION:

With slip rates of 15–25 mm/year along the Sagaing fault and a USGS-predicted death toll exceeding 10,000, the 2025 Myanmar quake highlights the urgency of enacting stringent building codes, rigorous retrofitting, and robust seismic preparedness. By prioritizing integrated disaster management strategies, early warning systems, and cross-border cooperation—especially in India, the region’s most quake-prone country—future seismic catastrophes can be significantly mitigated.

UPSC PAST YEAR QUESTION:

Q.1 Why are the world’s fold mountain systems located along the margins of continents? Bring out the association between the global distribution of Fold Mountains and the earthquakes and volcanoes. 2014

Q.2 Discuss about the vulnerability of India to earthquake related hazards. Give examples including the salient features of major disasters caused by earthquakes in different parts of India during the last three decades.

MAINS PRACTICE QUESTION:

Q.1 Discuss the tectonic significance of the Sagaing Fault in Myanmar and explain how oblique plate convergence influences the frequency and magnitude of earthquakes in South and Southeast Asia.

SOURCE:

https://www.thehindu.com/sci-tech/science/how-did-the-myanmar-earthquake-occur-explained/article69403721.ece

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