The Indo-Burman Arc is a convergent plate boundary connecting the Himalayan collision zone to the Sunda subduction system. It is defined by the oblique northeastward movement of the Indian Plate relative to the Eurasian Plate, resulting in a uniquely wide and seismically active deformation zone spanning from the Bay of Bengal to the Shan Plateau. Understanding its tectonic behavior is required for mitigating earthquake and tsunami risks in Myanmar, Northeast India, and surrounding regions.

Geological Framework of the Arc

Plate Kinematics and the Burma Platelet

The Indian Plate moves at a velocity of roughly 3.5 to 5 cm per year towards the northeast. This motion is not consumed along a single thrust fault. Instead, it is partitioned across a broad zone. The main subduction interface dips shallowly eastward beneath the Indo-Burman Ranges. East of the ranges, a crustal sliver known as the Burma Platelet takes up the along-strike component of the motion via strike-slip faulting. This kinematic partitioning is why the Indo-Burman Arc exhibits both megathrust potential and high-magnitude strike-slip events. Geodetic studies indicate that roughly half of the total convergence is accommodated by the Sagaing Fault, with the rest consumed within the accretionary wedge and the subduction interface.

Major Structural Elements

  • The Sagaing Fault: A 1,200 km dextral strike-slip fault. It is among the most active faults on Earth, exhibiting a slip rate of 18–20 mm/yr. It poses a direct hazard to Myanmar's population centers, running through Mandalay and Naypyidaw and passing close to Yangon.
  • The Churachandpur-Mao Fault (CMF): Located on the western flank of the Indo-Burman Ranges, this fault separates the accretionary wedge from the Indian Plate foreland. It is associated with moderate to large thrusting earthquakes in Manipur and Mizoram.
  • The Kabaw Fault: A major east-dipping reverse fault that forms the boundary between the Indo-Burman Ranges and the Central Myanmar Basin.
  • Andaman Spreading Center: The southern extension of the arc into the Andaman Sea features back-arc spreading, connecting the Sagaing Fault to the Sumatran fault system and complicating the regional stress regime.

Seismic Behavior and Rupture History

Great Historical Earthquakes

Paleoseismology has been instrumental in understanding the potential of the Indo-Burman megathrust. The most significant known event is the 1762 Arakan earthquake, estimated at magnitude 8.5 to 9.0. This earthquake generated a large tsunami and caused widespread coastal uplift, lifting coral reefs and shorelines by several meters. The rupture extended for over 500 km along the western coast of Myanmar and Bangladesh. This event serves as a strong analog for the type of worst-case scenario earthquake that the arc can produce.

Modern Seismicity and the Seismic Gap

Contemporary seismicity is dominated by upper plate crustal earthquakes and intraslab events rather than large megathrust ruptures. The 2016 Mw 6.9 Chauk earthquake and the 2012 Mw 6.8 Shwebo earthquake are examples of damaging events occurring within the Burma Platelet and along the Sagaing Fault. A notable seismic gap exists along the basal detachment of the Indo-Burman Ranges. GPS data show that strain is accumulating across the locked megathrust. If this locked segment ruptures in a single event, the earthquake could reach a magnitude of 8.5 or greater, releasing centuries of accumulated elastic energy. USGS hazard models classify this region as having high potential for large-magnitude events.

Active Tectonic Processes

The Subduction Zone

The Indian Plate subducts beneath the Burma Platelet at a very shallow angle. This low-angle geometry is largely due to the thick sedimentary pile of the Bengal Fan being carried into the trench. The thick sediment layer lubricates the interface to an extent but also creates a wide, locked zone capable of generating great tsunamigenic earthquakes. The shallow dip means that the seismogenic zone extends far inland, placing communities in the Indo-Burman Ranges directly above the rupture plane.

Strike-Slip Systems

The Sagaing Fault is a continental transform fault that accommodates the northward escape of the Burma Platelet relative to Sundaland. The fault is structurally immature in places, with highly linear segments that rupture in large earthquakes. Historical records show a pattern of major earthquakes on the Sagaing Fault occurring in sequences. Modern studies confirm that the fault is accumulating strain at a high rate, and the current period of relative quiescence on its central and southern segments is concerning for cities like Yangon. The Churachandpur-Mao Fault accommodates shortening on the western side of the arc, and while its slip rate is lower than the Sagaing Fault, its proximity to populated areas in Northeast India makes it a distinct hazard.

Geohazards and Regional Impact

Tsunami Potential

The 1762 Arakan earthquake demonstrated that the Indo-Burman Arc can generate destructive tsunamis. The shallow subduction and the presence of a large accretionary wedge create conditions for both uplift-driven and submarine landslide-triggered tsunami waves. The Bay of Bengal is densely populated along its coastlines, and a major tsunami wave could impact areas in Bangladesh, Myanmar, and eastern India within minutes to an hour. The Andaman and Nicobar Islands, lying directly east of the arc, are exposed to tsunami waves generated by ruptures on the eastern side of the arc as well.

Ground Deformation and Liquefaction

The Central Myanmar Basin, which contains the Irrawaddy River delta and the city of Yangon, is underlain by thick, soft sedimentary deposits. These deposits are highly susceptible to liquefaction during strong shaking. A large earthquake on the Sagaing Fault or the underlying megathrust would cause significant ground failure in Yangon, damaging port facilities, buildings, and critical infrastructure. The steep slopes of the Chin Hills and Naga Hills are vulnerable to widespread landsliding, which could block major routes and isolate communities following an earthquake.

Building Resilience

Seismic Monitoring and Research

In recent years, Myanmar has expanded its seismic network with support from international partners like the Earth Observatory of Singapore and the German Research Centre for Geosciences (GFZ). These networks provide real-time data for early warning and improve the understanding of fault behavior. However, coverage remains sparse in remote areas. Public access to seismic data and hazard maps is an ongoing area of development critical for urban planning and owner-driven reconstruction.

Engineering and Urban Planning

Myanmar has adopted a seismic design code for new buildings, but enforcement is limited outside of major government infrastructure projects. The rapid, unplanned urbanization of Yangon and Mandalay has resulted in many buildings constructed without formal engineering oversight. Research on seismic hazard models emphasizes the need for retrofitting existing structures, particularly schools and hospitals. In Northeast India, building codes have been updated following the 2016 Manipur earthquake, but similar challenges with enforcement persist.

Community Preparedness

Public awareness campaigns have been implemented in parts of Myanmar and Northeast India, focusing on evacuation drills and earthquake-resistant construction techniques. Local organizations are crucial for disseminating information in rural areas. The key challenge is moving from awareness to action, ensuring that households and communities take proactive steps to reduce their vulnerability. Preparedness efforts must account for the fact that the next large earthquake could occur on a megathrust, a fault system, or an intraslab source, each with distinct shaking and hazard characteristics.

The Indo-Burman Arc is a dynamic and geologically complex region where tectonic forces are constantly reshaping the landscape and accumulating strain. The science is clear on the potential for future large earthquakes. The path to resilience lies in translating this scientific understanding into effective building practices, land-use planning, and community-level preparedness. The arc's geological history is a record of powerful events, and its future will inevitably include more. The measure of success will be how well societies are equipped to withstand them.