What Caused the Myanmar Earthquake

On March 28, 2025, a devastating magnitude 7.7 earthquake struck central Myanmar, its epicenter just 12 miles from Mandalay. This powerful seismic event resulted in over 1,600 fatalities, thousands of injuries, and widespread structural damage. The primary cause lies in Myanmar's complex geology: a rupture occurred along the Sagaing Fault, a massive 1,200-kilometer tectonic boundary. Here, the Indian and Eurasian plates slide horizontally past each other in a strike-slip motion. Situated at the convergence of four plates Myanmar frequently experiences seismic activity, and this quake sent shockwaves across the nation and into neighboring Thailand.

Tectonic Setting of Myanmar

Myanmar is positioned at the convergence of several major tectonic plates, including the Indian, Eurasian, Sunda, and the Burman microplate. This complex tectonic interplay results in a seismically active region where compressional and lateral forces coexist. The northward movement of the Indian Plate relative to the Eurasian and Sunda Plates has generated widespread tectonic stress, contributing to the formation of mountain ranges and, importantly, a network of active fault systems across the region.

Key tectonic processes include:

• Plate Convergence: The collision between the Indian and Eurasian Plates, occurring at rates between 40–50 mm per year, builds up significant stress along plate boundaries.
• Subduction and Strike-Slip Motion: The interaction involving the Burma Plate and the Sunda Plate results in both compressional forces and lateral (strike-slip) movements, which are critical in understanding the seismic hazards in Myanmar.

Myanmar earthquake caused by a strike-slip fault rupture along the Sagaing Fault, due to tectonic plate movement between the Indian and Eurasian plates.

The Sagaing Fault: A Critical Seismic Feature

The Sagaing Fault is a prominent right-lateral (dextral) strike-slip fault that extends approximately 1,200 to 1,400 kilometers through central Myanmar. It forms a major boundary accommodating the relative movement between the tectonic plates in the region. This fault is essential for understanding the seismicity of Myanmar due to the following factors:

Strike-Slip Faulting: The horizontal movement of crustal blocks along the Sagaing Fault is a primary mechanism that releases accumulated tectonic stress. The fault’s characteristic right-lateral motion means that, from one side, the opposing side appears to move to the right.

Slip Rate and Stress Accumulation: With reported slip rates between 18 and 49 mm per year, the fault has continuously accumulated strain energy over time. The eventual release of this energy has been responsible for numerous seismic events, including historical earthquakes in 1912, 1839, and several significant events during the 20th century.

Rupture Characteristics: In the 2025 earthquake, seismic analyses indicated that the rupture extended between 200 km to 350 km along the fault, with a maximum slip reaching approximately 6.48 meters in some segments. The shallow rupture depth (around 10 km) was critical in amplifying the intensity of ground shaking.

How the 2025 Earthquake Occurred

The primary cause of the March 28, 2025 earthquake was the abrupt release of tectonic stress accumulated along the Sagaing Fault. This process is characterized by the following:

Stress Buildup and Release: The continuous northward movement of the Indian Plate relative to the Sunda Plate leads to significant frictional resistance along locked segments of the fault. When the accumulated stress exceeds the frictional strength, a sudden rupture occurs, releasing energy in the form of seismic waves.

Strike-Slip Motion: The earthquake was marked by horizontal displacement typical of strike-slip faulting. The lateral movement of the earth's crust generated by this fault mechanism resulted in rapid ground displacement over an extensive rupture area.

Shallow Focal Depth: The earthquake’s hypocenter was located at approximately 10 km below the surface. This shallow depth allowed seismic waves to travel with minimal energy loss, contributing to the severe shaking and extensive damage observed in central Myanmar and even in distant regions like Bangkok, Thailand.

Burma's tectonic plate, showing the convergence of the Indian, Eurasian, Sunda, and Burman microplate. Highlights seismic activity and fault lines like the Sagaing Fault, explaining regional earthquake risks.

Historical Context and Seismic Gaps

Historical records indicate that the Sagaing Fault has been responsible for numerous large earthquakes, with events of magnitude 7.0 or greater occurring over the past centuries. Notable historical seismicity includes:

• The 1912 event near Mandalay (magnitude ~7.9)
• The 1839 Ava earthquake (estimated magnitude 7.9)
• Various significant events during the 20th century

The concept of seismic gaps—segments along a fault that have not ruptured in an extended period—provides a critical context for the 2025 event. Prior studies had identified seismic gaps along central Myanmar, where prolonged periods of strain accumulation increased the potential for a large rupture. The location of the 2025 earthquake’s epicenter near such a gap underscores the importance of continuous seismic monitoring and updated hazard assessments in the region.

Impact and Regional Considerations

The earthquake’s shallow depth and extensive rupture had several profound impacts:

Structural Damage: The intense ground shaking resulted in the collapse of buildings and critical infrastructure such as bridges along major transportation routes, including the Yangon-Mandalay Expressway.

Casualties and Injuries: The reported death toll exceeded 1,600, with more than 3,400 individuals injured. The severity of the damage was compounded by the region’s vulnerability due to high population densities near major urban centers like Mandalay and Naypyidaw.

Wider Regional Effects: The event’s seismic waves extended far beyond Myanmar, with significant shaking felt in neighboring countries such as Thailand and southwest China. The collapse of a skyscraper under construction in Bangkok, over 600 miles from the epicenter, highlights the far-reaching influence of the earthquake.

Summary

The March 28, 2025 Myanmar earthquake was a result of the complex tectonic interplay in one of Southeast Asia’s most active seismic zones. The event was triggered by the abrupt release of stress along the Sagaing Fault, a major right-lateral strike-slip fault responsible for accommodating the regional tectonic movements. The shallow rupture depth and significant horizontal displacement contributed to the widespread and intense shaking, leading to substantial infrastructural damage and loss of life.

This seismic event reinforces the need for robust earthquake preparedness measures, enhanced building codes, and continuous geophysical monitoring to mitigate future risks in Myanmar. Understanding the mechanisms behind such earthquakes is crucial for improving seismic hazard assessments and ensuring public safety in tectonically active regions.