A small crustal block rotating independently between the Sunda and Burma plates. GPS measurements show it spins at 2 degrees per million years, complicating regional earthquake hazard models.
Alataristarion, CC BY-SA 4.0, via Wikimedia Commons
A Gear in the Earth's Crust
Off the coast of Myanmar's Tanintharyi Region, the Earth's crust is not a single, solid sheet. Here, sandwiched between the larger Sunda Plate and the Burma microplate, is a small, independent crustal block. This block, sometimes called the Belu Kyun microplate, rotates like a tectonic ball bearing. High-precision GPS measurements have detected this motion, revealing a slow, counter-clockwise spin of approximately two degrees every million years.
This tectonic feature is a result of regional forces. The Indian Plate has been driving northwards into the Eurasian continent for about 50 to 55 million years. This continental collision created the Himalayas and puts enormous strain on the entire Southeast Asian region. In Myanmar, this strain is primarily managed by the Sagaing Fault, a major right-lateral strike-slip fault that runs for over 1,400 kilometers through the country. The Sagaing Fault accommodates between 18 and 22 millimeters of north-south movement per year. The Belu Kyun microplate sits within this complex shear zone, its rotation a direct consequence of the immense forces acting upon the larger plates that surround it.
Complicating the Quake Question
The slow spin of this microplate is an important geological feature. Its movement absorbs some of the regional tectonic strain in a rotational fashion, rather than in a straightforward linear movement. This complicates scientific models used to assess earthquake hazards. The Sagaing Fault is one of the most seismically active fault systems in the region, responsible for large and destructive earthquakes.
Understanding how strain is distributed and where it is accumulating is important for forecasting future seismic risk. The rotation of the Belu Kyun block means that stress is not partitioned uniformly along the fault lines. Simple models that do not account for the block's rotation could miscalculate the strain building up in certain segments of the fault. The existence of this spinning microplate shows the complex and sometimes unexpected ways the Earth's crust deforms, requiring ever more detailed data to accurately model the planet's behavior and its potential hazards to populations living in tectonically active zones. The plate's motion is part of a larger system that includes the opening of the Andaman Sea to the south, which began in earnest around 4 million years ago.
💡Fun Facts
The microplate's rotation of 2 degrees per million years is extraordinarily slow. By comparison, a human fingernail grows roughly 3,000 billion times faster.
The feature is named after Belu Kyun, also known as "Ogre Island," a large island located near the city of Mawlamyine, north of the microplate's main offshore location.
Confirmation of the plate's rotation was only possible through networks of sensitive GPS stations capable of measuring millimeter-scale movements of the Earth's surface over several years.
This type of rotating crustal block is an important feature in "strain partitioning," where the force between two colliding plates is split into different types of motion, like slip on a fault and the rotation of an intermediary block.
Not applicable. This is a large-scale, mostly submarine geological feature.
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Accessibility
The microplate itself is an inaccessible feature of the Earth's crust in the Andaman Sea. The nearest accessible land is the coastline of the Tanintharyi Region.
