A Tectonically Active Collision Zone
The Salween River, one of Southeast Asia's last major free-flowing rivers, courses through a region of intense geological activity. Myanmar sits at the complex junction where the Indian Plate grinds northwards into the Eurasian Plate. This collision drives motion along major fault lines that slice through the country. The most important of these is the Sagaing Fault, a right-lateral strike-slip fault that extends for over 1,200 kilometers and accommodates a large portion of the tectonic strain.
Plans for a series of hydroelectric dams on the Salween, including the 1,360-megawatt Hatgyi Dam in Kayin State, place massive infrastructure directly within this seismically hazardous environment. The Hatgyi Dam site is located approximately 47 kilometers from the Thai-Myanmar border in an area of ecological and ethnic variety. While the major Sagaing Fault lies further west, other active fault lines, such as the Nampawng and Nam Ting faults, are in close proximity to proposed dam locations. Geological studies have confirmed that the broader region has a history of powerful earthquakes, including events of magnitude 7.0 or greater.
Reading the Ruptures
Scientists use a technique called paleoseismology to understand the earthquake history of a region where written records are sparse. By digging trenches directly across a fault line, geologists can read the layers of soil and rock. Displaced or folded layers reveal ancient surface-rupturing earthquakes. Studies along the Kyaukkyan Fault, another major fault system in eastern Myanmar, have used this method to identify multiple ruptures. Radiocarbon dating of organic material within these trenches showed evidence of a powerful earthquake that occurred sometime after 1270 ± 30 BP (Before Present).
This evidence of recent, significant seismic activity within the last millennium is an issue for dam construction. Beyond the risk of a natural earthquake, the immense weight of water in a large reservoir can itself trigger seismic events, known as reservoir-induced seismicity. Chinese earthquake specialists have specifically warned that the weight of a reservoir above a fault line is likely to trigger earthquakes, a primary reason why dam projects on the upper Salween (Nu River) in China were suspended. A dam failure at a site like Hatgyi could release a catastrophic volume of water, endangering downstream communities and ecosystems.